Categorized List

Journals

2023

1. Demonstration of Solute-specific Synergism in Binary Solvents. H. Ali and D. Goswami, Journal of Fluorescence 33(4), 1325–1335 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: The structure and solvation behavior of binary liquid mixtures of Methanol (MeOH) and N, N-Dimethylformamide (DMF) are explored by ascertaining their intermolecular interactions with either Rhodamine-B (RhB) or Rhodamine101 (Rh101) dye through steady-state absorption, emission, and two-photon induced fluorescence. Specifically, in the present investigation, we examine the strong synergistic solvation observed for the combinations of hydrogen bond donating (MeOH) and accepting (DMF) solvent pairs. Solvatochromism causes the solvatochromic probe molecules to sense increased polarity compared to their bulk counterparts. The origin of synergism was explained in terms of solute–solvent and solvent–solvent interactions in binary solvent mixtures interactions, as evidenced by probe dependence. The solvation behavior of the Methanol and DMF binary solvent mixture shows strong probe dependence, with Rh101 showing synergism while RhB does not.

    BibTeX: @article{aliDemonstrationSolutespecificSynergism2023,
     title = {Demonstration of {{Solute-specific Synergism}} in {{Binary Solvents}}},
     author = {Ali, Habib and Goswami, Debabrata},
     date = {2023-07-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {33},
     number = {4},
     pages = {1325--1335},
     issn = {1573-4994},
     doi = {10.1007/s10895-022-03141-8},
     url = {https://doi.org/10.1007/s10895-022-03141-8},
     urldate = {2023-07-28}
   }
   

2. Quality Assessment of the Commercially Available Alcohol-Based Hand Sanitizers with Femtosecond Thermal Lens Spectroscopy. S. Chakraborty, A. K. Rawat, A. K. Mishra, and D. Goswami, PeerJ Analytical Chemistry 5, e25 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: Using femtosecond-pulse-induced thermal lens spectroscopy (FTLS), we report a novel method for the quality measurements of alcohol-based hand sanitizers (ABHS). To sustain its effectiveness, the ABHS must contain the recommended concentration of alcohol content. We diluted the hand sanitizer with water to reduce the quantity of alcohol in the mixture and then performed thermal measurements on it. We performed both dual-beam Z-scan and time-resolved TL measurements to identify the alcoholic content in the ABHS. The thermal lens (TL) signal of the solvent is capable of detecting any relative change in the alcohol content in the mixture. Our technique, therefore, emerges as a sensitive tool for quality testing of alcohol-based hand sanitizers.

    BibTeX: @article{chakrabortyQualityAssessmentCommercially2023,
     title = {Quality Assessment of the Commercially Available Alcohol-Based Hand Sanitizers with Femtosecond Thermal Lens Spectroscopy},
     author = {Chakraborty, Subhajit and Rawat, Ashwini Kumar and Mishra, Amit Kumar and Goswami, Debabrata},
     date = {2023-05-30},
     journaltitle = {PeerJ Analytical Chemistry},
     shortjournal = {PeerJ An. Chem.},
     volume = {5},
     pages = {e25},
     publisher = {{PeerJ Inc.}},
     issn = {2691-6630},
     doi = {10.7717/peerj-achem.25},
     url = {https://peerj.com/articles/achem-25},
     urldate = {2023-07-28}
   }
   

3. Intense Femtosecond Optical Pulse Shaping Approaches to Spatiotemporal Control. D. Goswami, Frontiers in Chemistry 10, (2023) [Abstract] [PDF] [BibTeX]

   Abstract: For studying any event, measurement can never be enough; “control” is required. This means mere passive tracking of the event is insufficient and being able to manipulate it is necessary. To maximize this capability to exert control and manipulate, both spatial and temporal domains need to be jointly accounted for, which has remained an intractable problem at microscopic scales. Simultaneous control of dynamics and position of an observable event requires a holistic combination of spatial and temporal control principles, which gives rise to the field of spatiotemporal control. For this, we present a novel femtosecond pulse-shaping approach. We explain how to achieve spatiotemporal control by spatially manipulating the system through trapping and subsequently or simultaneously exerting temporal control using shaped femtosecond pulses. By leveraging ultrafast femtosecond lasers, the prospect of having temporal control of molecular dynamics increases, and it becomes possible to circumvent the relaxation processes at microscopic timescales. Optical trapping is an exemplary demonstration of spatial control that results in the immobilization of microscopic objects with radiation pressure from a tightly focused laser beam. Conventional single-beam optical tweezers use continuous-wave (CW) lasers for achieving spatial control through photon fluxes, but these lack temporal control knobs. We use a femtosecond high repetition rate (HRR) pulsed laser to bypass this lack of dynamical control in the time domain for optical trapping studies. From a technological viewpoint, the high photon flux requirement of stable optical tweezers necessitates femtosecond pulse shaping at HRR, which has been a barrier until the recent Megahertz pulse shaping developments. Finally, recognizing the theoretical distinction between tweezers with femtosecond pulses and CW lasers is of paramount interest. Non-linear optical (NLO) interactions must be included prima facie to understand pulsed laser tweezers in areas where they excel, like the two-photon-fluorescence-based detection. We show that our theoretical model can holistically address the common drawback of all tweezers. We are able to mitigate the effects of laser-induced heating by balancing this with femtosecond laser-induced NLO effects. An interesting side-product of HRR femtosecond-laser-induced thermal lens is the development of femtosecond thermal lens spectroscopy (FTLS) and its ability to provide sensitive molecular detection.

    BibTeX: @article{goswamiIntenseFemtosecondOptical2023,
     title = {Intense Femtosecond Optical Pulse Shaping Approaches to Spatiotemporal Control},
     author = {Goswami, Debabrata},
     date = {2023},
     journaltitle = {Frontiers in Chemistry},
     volume = {10},
     issn = {2296-2646},
     url = {https://www.frontiersin.org/articles/10.3389/fchem.2022.1006637},
     urldate = {2023-07-28}
   }
   

4. Exploring the Effects of Intermolecular Interactions on the Self-Defocusing of Binary Liquid Mixtures Using Single Beam z-Scan Technique - Asian Journal of Physics. R. K. Gupta, S. Kant, and D. Goswami, Asian Journal of Physics 31, 897–904 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: Self-defocusing (or negative lens effect) study of different sets of binary liquid mixtures having varying polarities has been carried out by employing a high repetition rate (HRR) femtosecond pulsed laser and utilising a single beam close aperture z-scan (CAZS) technique. We determined the change in transmittance values between peak and valley (ΔTp-v) of the CAZS trace for each different binary liquid mixtures at the varying composition of components. We correlated the variation of ΔTp-v values with the composition ratio of components to the change in physical parameters, which in turn affects the intermolecular interactions. Here, the combined effects of polarity differences and different molecular structures having steric hindrance are found to affect intermolecular interactions significantly in binary mixtures which in turn affect the self-defocusing effect.

    BibTeX: @article{guptaExploringEffectsIntermolecular2023,
     title = {Exploring the Effects of Intermolecular Interactions on the Self-Defocusing of Binary Liquid Mixtures Using Single Beam z-Scan Technique - {{Asian Journal}} of {{Physics}}},
     author = {Gupta, Rahul K. and Kant, Surya and Goswami, Debabrata},
     date = {2023-02-20},
     journaltitle = {Asian Journal of Physics},
     volume = {31},
     pages = {897--904},
     url = {https://asianjournalofphysics.com/exploring-the-effects-of-intermolecular-interactions-on-the-self-defocusing-of-binary-liquid-mixtures-using-single-beam-z-scan-technique/},
     urldate = {2023-07-28}
   }
   

5. Investigating the pH Dependence of Thermal Signatures in Monohydric and Polyhydric Alcohols Using Time-Resolved Thermal Lens Spectroscopy. A. K. Rawat, S. Chakraborty, A. K. Mishra, and D. Goswami, Optical Materials 137, 113623 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: We study the influence of pH on the thermophysical properties of monohydric and polyhydric alcohols through a femtosecond laser-induced thermal lens (TL) spectroscopic technique. Relative changes in the thermal signatures of monohydric and polyhydric alcohols are identified at different pH levels using both dual-beam Z-scan and time-resolved TL measurements. We found the TL signatures of the alcohols not to be affected in the acidic region, but a significant change is noticed in the alkaline environment. It is observed that in an alkaline environment (pH > 7), the TL signal significantly increases for short-chain (MeOH and EtOH) monohydric alcohols. In contrast, the TL signal for longer chain length monohydric alcohols (HxOH and phenol) and polyhydroxy alcohols (Ethylene glycol & Glycerol) fall enormously. These results depend strongly on the molecular characteristics of solvents and their interaction strength with the solute as a function of changing pH strength. Our results show the influence of pH on the natural drifting and the heat dissipation characteristics of solvent molecules, which prominently participate in changing the TL signatures of samples. This event could be attributed to changes in molecular arrangements by developing solvation shells (through ions-solvents interactions) in the systems. We investigate the influence of various factors, namely, chain length, structure, polarity, and inter or the intra-H-bonding ability of solvent molecules and ion concentration, which effectively alter the solute-solvent interaction strengths at different pH values (especially in an alkaline environment). The findings through our TL measurements explore this event in great detail for the first time. We try to correlate the molecular characteristics and its ions-solvent interaction effects with the thermophysical properties of alcohols.

    BibTeX: @article{rawatInvestigatingPHDependence2023,
     title = {Investigating the {{pH}} Dependence of Thermal Signatures in Monohydric and Polyhydric Alcohols Using Time-Resolved Thermal Lens Spectroscopy},
     author = {Rawat, Ashwini Kumar and Chakraborty, Subhajit and Mishra, Amit Kumar and Goswami, Debabrata},
     date = {2023-03-01},
     journaltitle = {Optical Materials},
     shortjournal = {Optical Materials},
     volume = {137},
     pages = {113623},
     issn = {0925-3467},
     doi = {10.1016/j.optmat.2023.113623},
     url = {https://www.sciencedirect.com/science/article/pii/S0925346723001957},
     urldate = {2023-07-28}
   }
   

2022

1. Electron Transfer, Spectroscopy and Theory: General Discussion. A. Anilkumar, P. Ash, A. R. Chakravarty, P. Comba, S. DeBeer, A. Dey, A. Draksharapu, D. Goswami, S. Itoh, K. Karlin, K. V. Lakshmi, S. Mazumdar, D. Pantazis, D. Parker, L. Que, G. Rajaraman, S. Prasad Rath, C. Sastri, S. S. Gupta, and E. I. Solomon, Faraday Discussions 234(0), 245–263 (2022) [PDF] [BibTeX]

    BibTeX: @article{anilkumarElectronTransferSpectroscopy2022,
     title = {Electron Transfer, Spectroscopy and Theory: General Discussion},
     shorttitle = {Electron Transfer, Spectroscopy and Theory},
     author = {Anilkumar, Anjali and Ash, Philip and R.~Chakravarty, Akhil and Comba, Peter and DeBeer, Serena and Dey, Abhishek and Draksharapu, Apparao and Goswami, Debabrata and Itoh, Shinobu and Karlin, Kenneth and V.~Lakshmi, K. and Mazumdar, Shyamalava and Pantazis, Dimitrios and Parker, David and Que, Lawrence and Rajaraman, Gopalan and Prasad~Rath, Sankar and Sastri, Chivukula and Gupta, Sayam Sen and I.~Solomon, Edward},
     date = {2022},
     journaltitle = {Faraday Discussions},
     volume = {234},
     number = {0},
     pages = {245--263},
     publisher = {{Royal Society of Chemistry}},
     doi = {10.1039/D2FD90013K},
     url = {https://pubs.rsc.org/en/content/articlelanding/2022/fd/d2fd90013k},
     urldate = {2022-12-31}
   }
   

2. Natural and Artificial Enzymes and Medicinal Aspects: General Discussion. P. Ash, A. R. Chakravarty, P. Comba, A. Dey, D. Goswami, C. Martin Jäger, K. Karlin, S. Kundu, S. L. Gatta, R. L. Domene, J.-D. Maréchal, S. Mazumdar, G. Mugesh, D. Pantazis, A. Pordea, P. J. Sadler, V. Schünemann, S. S. Gupta, O. Shoji, E. I. Solomon, P. Walton, and J. A. Wolny, Faraday Discussions 234(0), 367–387 (2022) [PDF] [BibTeX]

    BibTeX: @article{ashNaturalArtificialEnzymes2022,
     title = {Natural and Artificial Enzymes and Medicinal Aspects: General Discussion},
     shorttitle = {Natural and Artificial Enzymes and Medicinal Aspects},
     author = {Ash, Philip and R.~Chakravarty, Akhil and Comba, Peter and Dey, Abhishek and Goswami, Debabrata and Martin~Jäger, Christof and Karlin, Kenneth and Kundu, Subrata and Gatta, Salvatore La and Domene, Rocío López and Maréchal, Jean-Didier and Mazumdar, Shyamalava and Mugesh, Govindasamy and Pantazis, Dimitrios and Pordea, Anca and J.~Sadler, Peter and Schünemann, Volker and Gupta, Sayam Sen and Shoji, Osami and I.~Solomon, Edward and Walton, Paul and A.~Wolny, Juliusz},
     date = {2022},
     journaltitle = {Faraday Discussions},
     volume = {234},
     number = {0},
     pages = {367--387},
     publisher = {{Royal Society of Chemistry}},
     doi = {10.1039/D2FD90014A},
     url = {https://pubs.rsc.org/en/content/articlelanding/2022/fd/d2fd90014a},
     urldate = {2022-12-31}
   }
   

3. Sensing Non-Ideal Microheterogeneity in Binary Mixtures of Dimethyl Sulfoxide and Water. S. N. Bandyopadhyay, A. Singh, K. K. Singh, and D. Goswami, Journal of Optics 24(5), 054001 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: We present a microscopic study of water–dimethyl sulfoxide (DMSO) binary mixtures using optical tweezers and thermal lens techniques. Binary mixtures of DMSO with water show anomalous behavior due to the specific hydrogen bonding ability of DMSO. We use a tightly focused femtosecond laser at a low average power to optically trap microspheres with diameters of 1 micron for use as probes. The binary mixture exhibits various viscosities, depending on its composition ratio, and hence different trapped particle characteristic frequencies (corner frequencies) due to Brownian motion. The power spectrum density method is used to obtain the corner frequency from forward-scattered data. Thus, using low-power optical tweezer experiments, we find that the maximum viscosity occurs at a DMSO mole fraction of 0.276. At higher powers, the propensity for trapping is highly diminished. It may be surprising to note that these viscosity values obtained from the corner frequencies do not exactly match those published in the literature. However, this deviation can be attributed to the thermal behavior of the binary mixture, which affects the Brownian motion and hence the obtained viscosity values. Studies at the microscopic level can thus provide a newer perspective on these already important binary mixtures. Intensity-dependent measurements further confirm the contribution of thermal effects in this study.

    BibTeX: @article{bandyopadhyaySensingNonidealMicroheterogeneity2022,
     title = {Sensing Non-Ideal Microheterogeneity in Binary Mixtures of Dimethyl Sulfoxide and Water},
     author = {Bandyopadhyay, Soumendra Nath and Singh, Ajitesh and Singh, Krishna Kant and Goswami, Debabrata},
     date = {2022-05-01},
     journaltitle = {Journal of Optics},
     shortjournal = {J. Opt.},
     volume = {24},
     number = {5},
     pages = {054001},
     issn = {2040-8978, 2040-8986},
     doi = {10.1088/2040-8986/ac50ff},
     url = {https://iopscience.iop.org/article/10.1088/2040-8986/ac50ff},
     urldate = {2022-12-31}
   }
   

4. An Investigation of Evanescent Wave-Induced Fluorescence Spectroscopy for Exploring High Refractive Index Media. S. Chakraborty, Y. Xu, A. Roberts, D. Goswami, and T. A. Smith, Physica Scripta 98(1), 015014 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Evanescent wave-induced fluorescence spectroscopy (EWIFS) is a widely used technique for probing the interfacial behavior of different complex media in investigations of samples in the physical, chemical, and biological sciences. This technique takes advantage of the sharply decaying evanescent field, established following total internal reflection (TIR) at the interface of two media, for spatially identifying the photoluminescence characteristics of the sample. The generation of the evanescent field requires the refractive index of the second medium to be lower than that of the first, so a major disadvantage of this increasingly widely used spectroscopic technique is the inability to exploit the advantages of EWIFS to image a sample with a higher refractive index than the incident substrate medium. A proposed configuration in which a thin, low refractive index intermediate layer is established between the TIR substrate and a high refractive index sample is investigated. We illustrate that this arrangement does not afford the desired advantages of evanescent field-induced fluorescence measurements for investigating high refractive index media.

    BibTeX: @article{chakrabortyInvestigationEvanescentWaveinduced2022,
     title = {An Investigation of Evanescent Wave-Induced Fluorescence Spectroscopy for Exploring High Refractive Index Media},
     author = {Chakraborty, Subhajit and Xu, Yang and Roberts, Ann and Goswami, Debabrata and Smith, Trevor A.},
     date = {2022-12},
     journaltitle = {Physica Scripta},
     shortjournal = {Phys. Scr.},
     volume = {98},
     number = {1},
     pages = {015014},
     publisher = {{IOP Publishing}},
     issn = {1402-4896},
     doi = {10.1088/1402-4896/aca437},
     url = {https://dx.doi.org/10.1088/1402-4896/aca437},
     urldate = {2022-12-31}
   }
   

5. Probing Solvent Dependent Femtosecond Transient Coherent Oscillations to Reveal Interfacial Dynamics. D. K. Das, K. Makhal, and D. Goswami, Journal of Optics 24(6), 063001 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Probing transient states in molecules having vibronic transitions with femtosecond (fs) laser pulses often results in coherent oscillations either in the ground state, the excited states, or both. We find such coherent oscillations are highly solvent-dependent and provide a holistic overview of the pump-probe experiments for ultrafast dye dynamics at interfaces. For molecules dissolved in single solvents, modulations in oscillations occur due to transitions in the sub-vibrational levels of the electronic state. For binary solvents, in particular, these modulations are strongly sensitive to solvent compositions. The changes induced by various solvent compositions are drastic enough to act as a control parameter for dynamical control processes. We demonstrate an end-to-end understanding of ground-state coherent oscillations, vibrational cooling, ground-state recovery processes, and excited-state dynamics through a series of experiments. We further present a methodology for establishing such control using near-infrared dyes to measure the oscillations with fs pump-probe techniques. In the case of immiscible binary solvents, the same method allows us to investigate the liquid–liquid interface. Our control methodology is validated by an experiment using a cyanine dye dissolved in dimethyl sulfoxide, interfaced with neat diethyl-ether. The dye dynamics are retarded on moving from the bulk dye solution towards the interface with the neat diethyl-ether. When sampled along the direction of the vector pointing from the bulk towards the near interface, monotonically decreasing time constants are obtained. This result strongly suggests the importance of microheterogeneity in interfacial dynamics.

    BibTeX: @article{dasProbingSolventDependent2022,
     title = {Probing Solvent Dependent Femtosecond Transient Coherent Oscillations to Reveal Interfacial Dynamics},
     author = {Das, D. K. and Makhal, K. and Goswami, Debabrata},
     date = {2022-05},
     journaltitle = {Journal of Optics},
     shortjournal = {J. Opt.},
     volume = {24},
     number = {6},
     pages = {063001},
     publisher = {{IOP Publishing}},
     issn = {2040-8986},
     doi = {10.1088/2040-8986/ac675b},
     url = {https://dx.doi.org/10.1088/2040-8986/ac675b},
     urldate = {2022-12-31}
   }
   

6. Investigating the Effects of Intermolecular Interactions on Nonlinear Optical Properties of Binary Mixtures with High Repetition Rate Femtosecond Laser Pulses. R. K. Gupta, S. Verma, S. Singhal, S. Kant, and D. Goswami, PeerJ Physical Chemistry 4, e23 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Measurements of nonlinear optical (NLO) properties of different binary mixtures having carbon disulfide (CS2) as the common component, namely CS2-acetone, CS2-cyclopentanone, CS2-toluene, and CS2-carbon tetrachloride (CCl4), are carried out by using the z-scan technique. Open-aperture z-scan (OAZS) and close-aperture z-scan (CAZS) experiments are performed to determine the nonlinear absorption coefficient (β) and nonlinear refractive index (n2) of all binary liquid mixtures at various compositions of the components by employing a pulsed, high repetition rate (HRR) femtosecond laser. Also, we were able to use the flowing liquid to measure NLO properties in the CS2-acetone binary mixture to remove the cumulative thermal effects produced due to the pulsed HRR laser light. Nonlinear refractive index (n2) values are found to be influenced by the weak dipole-induced dipole intermolecular interactions between the nonpolar CS2 and polar acetone as well as cyclopentanone of the respective binary mixtures. On the contrary n2 values are not found to be affected by the intermolecular interactions in CS2-toluene and CS2-CCl4 binary mixtures. In comparison, the nonlinear absorption coefficient (β) values are not found to be affected by the same in all different sets of binary mixtures.

    BibTeX: @article{guptaInvestigatingEffectsIntermolecular2022,
     title = {Investigating the Effects of Intermolecular Interactions on Nonlinear Optical Properties of Binary Mixtures with High Repetition Rate Femtosecond Laser Pulses},
     author = {Gupta, Rahul Kumar and Verma, Sachin and Singhal, Sumit and Kant, Surya and Goswami, Debabrata},
     date = {2022-06-07},
     journaltitle = {PeerJ Physical Chemistry},
     shortjournal = {PeerJ Phy. Chem.},
     volume = {4},
     pages = {e23},
     publisher = {{PeerJ Inc.}},
     issn = {2689-7733},
     doi = {10.7717/peerj-pchem.23},
     url = {https://peerj.com/articles/pchem-23},
     urldate = {2022-12-31}
   }
   

7. Achieving Molecular Distinction in Alcohols with Femtosecond Thermal Lens Spectroscopy. A. Kumar Rawat, S. Chakraborty, A. Kumar Mishra, and D. Goswami, Chemical Physics 561, 111596 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Using thermal lens (TL) spectroscopy, we distinguish monohydric alcohols based on their molecular characteristics and thermophysical properties. We use both dual-beam Z-scan and time-resolved TL measurements to identify thermal signatures of the representative homologous series of aliphatic, cyclic, and aromatic alcohols. While, in aliphatic alcohols, TL signal amplitude depends strongly on the molecular size and chain length; for cyclic and aromatic alcohols, their photophysical characteristics exhibit dominance over the molecular influence of TL signal. The convective properties of short-chain molecules result in a characteristic trend in dual-beam experiments. Methanol displays the lowest steady-state TL signal due to its fast diffusive capabilities. At the same time, phenol shows the most prominent steady-state TL signal owing to its strong H-bonded cluster formation ability through resonant structures. TL measurements successfully distinguish alcohols belonging to the respective homologous series and additionally discern solvents with a similar number of carbon atoms belonging to different homologous series.

    BibTeX: @article{kumarrawatAchievingMolecularDistinction2022,
     title = {Achieving Molecular Distinction in Alcohols with Femtosecond Thermal Lens Spectroscopy},
     author = {Kumar Rawat, Ashwini and Chakraborty, Subhajit and Kumar Mishra, Amit and Goswami, Debabrata},
     date = {2022-09-01},
     journaltitle = {Chemical Physics},
     shortjournal = {Chemical Physics},
     volume = {561},
     pages = {111596},
     issn = {0301-0104},
     doi = {10.1016/j.chemphys.2022.111596},
     url = {https://www.sciencedirect.com/science/article/pii/S0301010422001513},
     urldate = {2022-12-31}
   }
   

8. Poly-Lysinated Nanoscale Carbon Probe for Low Power Two-Photon Bioimaging. S. Kundu, N. Chatterjee, S. Chakraborty, A. Gupta, D. Goswami, and S. K. Misra, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 270, 120778 (2022) [BibTeX]

    BibTeX: @article{kunduPolylysinatedNanoscaleCarbon2022,
     title = {Poly-Lysinated Nanoscale Carbon Probe for Low Power Two-Photon Bioimaging},
     author = {Kundu, Sayan and Chatterjee, Niranjan and Chakraborty, Subhajit and Gupta, Arjit and Goswami, Debabrata and Misra, Santosh K.},
     date = {2022},
     journaltitle = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
     volume = {270},
     pages = {120778},
     publisher = {{Elsevier}}
   }
   

9. ‪Control of Selective Two-Photon Fluorescence Suppression by One-Color Pulse-Pair Excitation‬. D. Roy, A. K. De, and D. Goswami, Asian Journal of Physics 31(3-5), 475–478 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: For studying the selective excitation of a particular fluorophore in fluorescence microscopy, the effect of the laser pulse chosen is immense. To study the ramifications of this selection, we present a thorough study of one-color stimulated emission depletion of the two-photon fluorescence of selective fluorophores by changing the wavelength and delay between two identical laser pulses.

    BibTeX: @article{royControlSelectiveTwophoton2022,
     title = {‪{{Control}} of Selective Two-Photon Fluorescence Suppression by One-Color Pulse-Pair Excitation‬},
     author = {Roy, Debjit and De, Arijit K. and Goswami, Debabrata},
     date = {2022},
     journaltitle = {Asian Journal of Physics},
     volume = {31},
     number = {3-5},
     pages = {475--478},
     url = {https://scholar.google.com/citations?view_op=view_citation&hl=en&user=OZ651FIAAAAJ&sortby=pubdate&citation_for_view=OZ651FIAAAAJ:jtI9f0ekYq0C},
     urldate = {2022-12-31}
   }
   

2021

1. Unraveling Molecular Interactions in Binary Liquid Mixtures with Time-Resolved Thermal-Lens-Spectroscopy. A. K. Rawat, S. Chakraborty, A. K. Mishra, and D. Goswami, Journal of Molecular Liquids 336, 116322 (2021) [Abstract] [PDF] [BibTeX]

   Abstract: Non-contact localized laser heating-based thermal lensing has emerged as a technique for probing the heat transport in liquids. A mode-mismatched dual-beam pump–probe spectroscopic technique was employed to investigate the photothermal response and modes of heat dissipation in methanol and binary mixtures of methanol with polar (water, methanol (MeOH)) and nonpolar (CCl4) solvents. We recorded the time-resolved thermal lens (TL) signal of a probe beam at 780 nm after heat deposition by a 1560 nm pump beam. For pure solvents, the TL signal was found to be approximately one order of magnitude larger for methanol than for water, DMSO, or CCl4, implying that the energy deposition is larger for methanol than for any of the other solvents. Subsequently, binary mixtures were studied where the TL signal increased with an increase in the volume fraction of methanol. All TL signals are shown to have a physical interpretation in terms of heat conduction and convection. In the case of methanol–water, the observed trend can be rationalized in terms of a strong intermolecular interaction. Convective heat transfer is shown to dominate the overall heat transfer in pure methanol and in binary mixtures for all volume fractions where MeOH is in excess of 50%. No convection is observed for very dilute mixtures with a small amount of methanol; in this case, heat conduction is sufficient to reach equilibration. Interestingly, for binary mixtures of methanol with DMSO or water, a decreasing trend is observed in the concentration range between 90% and 100% volume fraction of methanol. We observe also that the TL signal is modified in case of intermolecular interactions forming large clusters of methanol with the cosolvent. In such cases, heat diffusion is affected. Thus, TL can be seen as a sensitive probe for intermolecular interactions as well.

    BibTeX: @article{rawatUnravelingMolecularInteractions2021,
     title = {Unraveling Molecular Interactions in Binary Liquid Mixtures with Time-Resolved Thermal-Lens-Spectroscopy},
     author = {Rawat, Ashwini Kumar and Chakraborty, Subhajit and Mishra, Amit Kumar and Goswami, Debabrata},
     date = {2021-08-15},
     journaltitle = {Journal of Molecular Liquids},
     shortjournal = {Journal of Molecular Liquids},
     volume = {336},
     pages = {116322},
     issn = {0167-7322},
     doi = {10.1016/j.molliq.2021.116322},
     url = {https://www.sciencedirect.com/science/article/pii/S0167732221010461},
     urldate = {2023-07-28}
   }
   

2020

1. Organic-Inorganic Hybrid Halide Perovskites Impregnated with Group 1 and 15 Elements for Solar Cell Application. P. Dey, H. Singh, R. K. Gupta, D. Goswami, and T. Maiti, Journal of Physics and Chemistry of Solids 144, 109518 (2020) [Abstract] [PDF] [BibTeX]

   Abstract: In this report, we explored the substitution of triple cations at B-site of ABX3 perovskite architecture in inorganic-organic hybrid perovskite materials in order to improve its stability over moisture and heat, which is considered as the paramount obstacles for commercialization of perovskite solar cell. In the current investigation we synthesized two novel perovskite materials, Methylammonium potassium bismuth lead iodide [CH3NH3K0.25Bi0.25Pb0.5I3] (MKBPI) and Methylammonium sodium bismuth lead iodide [CH3NH3Na0.25Bi0.25Pb0.5I3] (MNBPI). XRD studies confirmed hexagonal crystal structure with P63/mmc space group for both the perovskites. Antisolvent treatment improved the surface coverage and morphology of the thin films, observed in FESEM. UV–Vis spectra demonstrated high absorption coefficient. Band gap was estimated as 2.09 eV for MKBPI. Fluorescence decay kinetics study revealed charge carrier lifetime on the order of nano second. DSC and TGA measurements confirmed thermal stability of these perovskites up to 280 °C. Further, we carried out detailed degradation study using XRD and UV–Vis spectroscopy of these perovskite thin films kept at ambient atmosphere for two weeks. Remarkably thin films of these perovskites exhibited good absorption even after 14 days.

    BibTeX: @article{deyOrganicinorganicHybridHalide2020,
     title = {Organic-Inorganic Hybrid Halide Perovskites Impregnated with {{Group}} 1 and 15 Elements for Solar Cell Application},
     author = {Dey, Pritam and Singh, Harish and Gupta, Rahul K. and Goswami, Debabrata and Maiti, Tanmoy},
     date = {2020-09-01},
     journaltitle = {Journal of Physics and Chemistry of Solids},
     shortjournal = {Journal of Physics and Chemistry of Solids},
     volume = {144},
     pages = {109518},
     issn = {0022-3697},
     doi = {10.1016/j.jpcs.2020.109518},
     url = {http://www.sciencedirect.com/science/article/pii/S0022369719327763},
     urldate = {2020-07-11}
   }
   

2. Vectorial Imaging Techniques for Insights into the Principles of Optical Tweezers. S. Dinda and D. Goswami, Asian Journal of Physics 28(10-12), 989–1013 (2020) [Abstract] [BibTeX]

   Abstract: Optical tweezers work on the principle that microscopic particles may be immobilized by the application of an intense photon flux, which may be attained under tight focusing conditions. To elucidate the behaviour and mechanism of this tweezing action, herein we perform numerical studies and investigate the intensity distribution at the focusing spot under tight focusing conditions. With a high numerical aperture optical lens, the influence of the incident beam polarization on the intensity distribution of focusing spot is very significant. A linearly polarized incident beam induces an asymmetric focusing spot, which is elongated along the polarization direction of the incident beam. The incident beam profile influences the shape of the focusing spot. We show here how introducing an optical mask in front of the optical lens can induce many impressive results; e.g., incident beam modulated by an amplitude mask induces a sub-diffraction limit focusing spot which is relevant to further studies on optical tweezers. We also demonstrate the effects of considering interfaces of different numerical apertures in an optical setup. Thus, we report on the multiple aspects of light-matter interactions for high numerical aperture lens setups, wherein we show through simulations and experiments, the characteristics of such systems that are of use to the broader optics community.

    BibTeX: @article{dindaVectorialImagingTechniques2020,
     title = {Vectorial Imaging Techniques for Insights into the Principles of Optical Tweezers},
     author = {Dinda, Sirshendu and Goswami, Debabrata},
     date = {2020-05-01},
     journaltitle = {Asian Journal of Physics},
     shortjournal = {Asian J. Phys.},
     volume = {28},
     number = {10-12},
     pages = {989--1013}
   }
   

3. Arthur Ashkin (1922–2020). S. Goswami and D. Goswami, Current Science 120(4), 726–728 (2020) [BibTeX]

    BibTeX: @article{goswamiArthurAshkin19222020,
     title = {Arthur {{Ashkin}} (1922–2020)},
     author = {Goswami, Sonaly and Goswami, Debabrata},
     date = {2020},
     journaltitle = {Current Science},
     volume = {120},
     number = {4},
     pages = {726--728},
     issn = {0028-0836, 1476-4687}
   }
   

4. Femtosecond Pump-Probe Spectroscopy for Remote Sensing of Liquid-Liquid Interface. D. Goswami, D. K. Das, and K. Makhal, Asian Journal of Physics 29(3 & 4), 313–319 (2020) [Abstract] [BibTeX]

   Abstract: We report results establishing that detection of the liquid-liquid interface is possible through femtosecond pump-probe spectroscopy. In particular, we use femtosecond laser pulses to pump and probe the dynamics of infra-red dye molecules in a liquid pair that can form an interface. We demonstrate that an interface formation can be detected from such femtosecond dynamical study of the dye molecule. The importance of obtaining the molecular description on the relation between the dynamics of solute molecules and solute-solvent interactions arises from the fact that the dynamic and static properties of dye molecules are strongly affected by the surrounding solvent molecules.

    BibTeX: @article{goswamiFemtosecondPumpprobeSpectroscopy2020,
     title = {Femtosecond Pump-Probe Spectroscopy for Remote Sensing of Liquid-Liquid Interface},
     author = {Goswami, Debabrata and Das, Dipak K. and Makhal, Krishnandu},
     date = {2020},
     journaltitle = {Asian Journal of Physics},
     volume = {29},
     pages = {313--319},
     issue = {3\&4}
   }
   

5. Nicolaas Bloembergen (1920–2017): Physicist, Father of Nonlinear Optics. D. Goswami, Resonance 25(12), 1653–1657 (2020) [PDF] [BibTeX]

    BibTeX: @article{goswamiNicolaasBloembergen19202020,
     title = {Nicolaas {{Bloembergen}} (1920–2017): {{Physicist}}, {{Father}} of {{Nonlinear Optics}}},
     shorttitle = {Nicolaas {{Bloembergen}} (1920–2017)},
     author = {Goswami, Debabrata},
     date = {2020-12},
     journaltitle = {Resonance},
     shortjournal = {Reson},
     volume = {25},
     number = {12},
     pages = {1653--1657},
     issn = {0971-8044, 0973-712X},
     doi = {10/gjmhvg},
     url = {http://link.springer.com/10.1007/s12045-020-1086-8},
     urldate = {2021-03-28}
   }
   

6. Two-Photon-Induced Fluorescence Study of Rhodamine-6G Dye in Different Sets of Binary Solvents. R. K. Gupta, S. Kant, A. K. Rawat, and D. Goswami, Journal of Fluorescence (2020) [Abstract] [PDF] [BibTeX]

   Abstract: This study deals with the effects of different sets of binary solvents on the Two-Photon Induced Fluorescence (TPIF), a non-linear process, of the Rhodamine-6G (Rh6G) dye, which is a well-known xanthene dye. This work examines the importance of inter-molecular interactions, which results in the modulation of the TPIF of the Rh6G. In this work, we have investigated three binary solvent mixtures representing varying polarity and intermolecular interactions. Specific solvent mixtures used are methanol-water, methanol-dimethyl formamide, and methanol-chloroform. Since the solvent polarity across these binary solvents differs, there are significant intermolecular interactions in the binary mixture solvents, which modulate the two-photon process of Rh6G when irradiated with high-intensity laser light at 780 nm. In our studies, we find that Rh6G in the MeOH-H2O binary solvent has maximum red-shift and minimum intensity as compared to other pairs of binary liquids when the volume fraction of methanol decreases due to more extensive hydrogen bonding between the two components. Additionally, at 1:1 ratio of binary mixtures, Rh6G is found to have the highest TPEACS value for methanol-chloroform binary solvent and reason for that is related to the formation of weak H-bond networks between proton donor chloroform and proton acceptor methanol.

    BibTeX: @article{guptaTwoPhotonInducedFluorescenceStudy2020,
     ids = {guptaTwoPhotonInducedFluorescenceStudy2020a},
     title = {Two-{{Photon-Induced Fluorescence Study}} of {{Rhodamine-6G Dye}} in {{Different Sets}} of {{Binary Solvents}}},
     author = {Gupta, Rahul Kumar and Kant, Surya and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2020-07-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     issn = {1573-4994},
     doi = {10.1007/s10895-020-02577-0},
     url = {10.1007/s10895-020-02577-0},
     urldate = {2020-07-11}
   }
   

7. Unraveling the Molecular Dependence of Femtosecond Laser-Induced Thermal Lens Spectroscopy in Fluids. S. Singhal and D. Goswami, The Analyst 10.1039.C9AN01082C (2020) [Abstract] [PDF] [BibTeX]

   Abstract: Fluid systems exhibit thermal lens effects due to laser irradiation accompanied by convection and in contrast primarily conductive heat dissipation is observed in solids. , Fluid systems exhibit thermal lens effects due to laser irradiation accompanied by convection and in contrast primarily conductive heat dissipation is observed in solids. The presence of a significant convective mode modifies the temperature gradient in fluids resulting in a deviation of the experimental results from theories that are based on pure conduction. Herein, we present a carefully designed femtosecond laser experiment that keeps the heat generation process constant in order to account for the effect of molecular properties on thermal dissipation. We derive a theoretical model that introduces and characterizes the additional convective heat transfer in thermal lens (TL) spectroscopy which explains our observed experimental results. We measured the TL signal for a series of liquid aliphatic alkanes, ranging from hexane to decane, and their comparison has proven the validity of our model. The influence of convective heat transfer on the TL signal is predicted in terms of the dimensionless Peclet number ( P E ). The lower values of P E for alkanes with longer carbon chains indicate that the convective flow of heat slows down substantially for larger molecules.

    BibTeX: @article{singhalUnravelingMolecularDependence2020,
     title = {Unraveling the Molecular Dependence of Femtosecond Laser-Induced Thermal Lens Spectroscopy in Fluids},
     author = {Singhal, Sumit and Goswami, Debabrata},
     date = {2020},
     journaltitle = {The Analyst},
     shortjournal = {Analyst},
     pages = {10.1039.C9AN01082C},
     issn = {0003-2654, 1364-5528},
     doi = {10/ggfxvz},
     url = {http://xlink.rsc.org/?DOI=C9AN01082C},
     urldate = {2019-12-28}
   }
   

2019

1. Rapid Programmable Pulse Shaping of Femtosecond Pulses at the MHz Repetition Rate. S. Dinda, S. N. Bandyopadhyay, and D. Goswami, OSA Continuum 2(4), 1386 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: We have shown experimentally the successful engineering of femtosecond pulse shaping at a 76 MHz repetition rate input pulse with an acousto-optic modulator (AOM). High repetition rate (HRR) femtosecond laser pulse shaping using an AOM in the Fourier plane was incomprehensible because of its intrinsic 100 kHz acoustic update limit. We demonstrate an effective way of pulse selection and a calibration routine (Fourier shift theorem), which enables generation of ∼10 MHz shaped output pulses from the HRR input pulse train. We have generated a temporally shifted rectangular shaped pulse profile by applying modulation on both the phase and amplitude of the ‘sinc’ RF modulation function.

    BibTeX: @article{dindaRapidProgrammablePulse2019,
     title = {Rapid Programmable Pulse Shaping of Femtosecond Pulses at the {{MHz}} Repetition Rate},
     author = {Dinda, Sirshendu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2019-04-15},
     journaltitle = {OSA Continuum},
     shortjournal = {OSA Continuum},
     volume = {2},
     number = {4},
     pages = {1386},
     issn = {2578-7519},
     doi = {10/gf4gtf},
     url = {https://www.osapublishing.org/abstract.cfm?URI=osac-2-4-1386},
     urldate = {2019-06-30}
   }
   

2. Excited State Absorption and Relaxation Dynamics in a Series of Heptamethine Dyes under Femtosecond and Nanosecond Excitations. K. Makhal, S. Maurya, and D. Goswami, Physica Scripta 94(9), 095501 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: We show that the near-infrared-absorbing polymethine cyanine dyes exhibit nonlinear absorption (NLA) in the visible region, where they have negligible or very low linear absorption. In chloroform solvent, the studied cyanines were found to be photo-unstable and exhibited photo-degradation under prolonged exposures as compared to methanol and dimethyl sulphoxide solvents, where they were stable. Excitation with femtosecond (fs) pulses in the visible region (400–750 nm) exhibits excited state absorption (ESA) as characterized by positive differential absorption (ΔOD) in transient absorption signal. Non-resonant excitations in the visible region are governed by reverse saturable absorption (RSA) mechanism leading to ESA. Excitation with nanosecond pulses also shows NLA owing to ESA from triplet states as compared to that from singlet states under fs excitations. Single beam Z-scan studies were performed with nanosecond (ns) pulses to evaluate ground (σ gr) and excited state (σ ex) absorption cross-sections, which confirms the mechanism of RSA as σ ex were found to be greater than σ gr. The population relaxation from higher excited singlet states shows ultrafast behavior with multi-exponential decay components. The fast time component decay varies from a few hundreds of fs (τ 1) to some hundreds of picoseconds (τ 2), and the long-time decay is in the ns domain (τ 3).

    BibTeX: @article{makhalExcitedStateAbsorption2019,
     title = {Excited State Absorption and Relaxation Dynamics in a Series of Heptamethine Dyes under Femtosecond and Nanosecond Excitations},
     author = {Makhal, Krishnandu and Maurya, Sidharth and Goswami, Debabrata},
     date = {2019-06},
     journaltitle = {Physica Scripta},
     shortjournal = {Phys. Scr.},
     volume = {94},
     number = {9},
     pages = {095501},
     issn = {1402-4896},
     doi = {10/gf5mpz},
     url = {https://doi.org/10.1088%2F1402-4896%2Fab0064},
     urldate = {2019-08-01}
   }
   

3. Effect of Femtosecond Laser Pulse Repetition Rate on Nonlinear Optical Properties of Organic Liquids. S. K. Maurya, D. Yadav, and D. Goswami, PeerJ Physical Chemistry 1, e1 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: The effect of the repetition rate of femtosecond laser pulses on the two-photon absorption and nonlinear refraction of pure organic liquids is presented using the conventional Z-scan technique. Such a study provides a way to determine the nature of light-matter interaction, explicitly enabling the identification of the linear versus nonlinear regimes. Based on the type of light-matter interaction, we have identified the thermal load dissipation time for the organic liquids. Our experimental results are in good agreement with the theoretically calculated decay time for the dissipation of thermal load.

    BibTeX: @article{mauryaEffectFemtosecondLaser2019,
     title = {Effect of Femtosecond Laser Pulse Repetition Rate on Nonlinear Optical Properties of Organic Liquids},
     author = {Maurya, Sandeep Kumar and Yadav, Dheerendra and Goswami, Debabrata},
     date = {2019-10-15},
     journaltitle = {PeerJ Physical Chemistry},
     volume = {1},
     pages = {e1},
     doi = {10/ggbzhh},
     url = {https://peerj.com/articles/pchem-1},
     urldate = {2019-10-29}
   }
   

4. Elucidating Optical Field Directed Hierarchical Self-Assembly of Homogenous versus Heterogeneous Nanoclusters with Femtosecond Optical Tweezers. D. Mondal, S. N. Bandyopadhyay, and D. Goswami, PLOS ONE 14(10), e0223688 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: Insights into the morphology of nanoclusters would facilitate the design of nano-devices with improved optical, electrical, and magnetic responses. We have utilized optical gradient forces for the directed self-assembly of colloidal clusters using high-repetition-rate femtosecond laser pulses to delineate their structure and dynamics. We have ratified our experiments with theoretical models derived from the Langevin equation and defined the valid ranges of applicability. Our femtosecond optical tweezer-based technique characterizes the in-situ formation of hierarchical self-assembled clusters of homomers as well as heteromers by analyzing the back focal plane displacement signal. This technique is able to efficiently distinguish between nano-particles in heterogeneous clusters and is in accordance with our theory. Herein, we report results from our technique, and also develop a model to describe the mechanism of such processes where corner frequency changes. We show how the corner frequency changes enables us to recognize the structure and dynamics of the coagulation of colloidal homogeneous and heterogeneous clusters in condensed media over a broad range of nanoparticle sizes. The methods described here are advantageous, as the backscatter position-sensitive detection probes the in-situ self-assembly process while other light scattering approaches are leveraged for the characterization of isolated clusters.

    BibTeX: @article{mondalElucidatingOpticalField2019,
     title = {Elucidating Optical Field Directed Hierarchical Self-Assembly of Homogenous versus Heterogeneous Nanoclusters with Femtosecond Optical Tweezers},
     author = {Mondal, Dipankar and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2019-10-31},
     journaltitle = {PLOS ONE},
     shortjournal = {PLOS ONE},
     volume = {14},
     number = {10},
     pages = {e0223688},
     issn = {1932-6203},
     doi = {10/ggfxvx},
     url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0223688},
     urldate = {2019-12-28}
   }
   

5. Polarization Induced Control of Optical Trap Potentials in Binary Liquids. D. Mondal, S. Dinda, S. N. Bandyopadhyay, and D. Goswami, Scientific Reports 9(1), 700 (2019) [PDF] [BibTeX]

    BibTeX: @article{mondalPolarizationInducedControl2019,
     title = {Polarization Induced Control of Optical Trap Potentials in Binary Liquids},
     author = {Mondal, Dipankar and Dinda, Sirshendu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2019-12},
     journaltitle = {Scientific Reports},
     shortjournal = {Sci Rep},
     volume = {9},
     number = {1},
     pages = {700},
     issn = {2045-2322},
     doi = {10/gf5mqb},
     url = {http://www.nature.com/articles/s41598-018-36856-5},
     urldate = {2019-08-01}
   }
   

6. Thermal Lens Study of NIR Femtosecond Laser-Induced Convection in Alcohols. S. Singhal and D. Goswami, ACS Omega 4(1), 1889–1896 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: We use time-resolved thermal lens (TL) experiments to examine the convective heat transfer at microscale in the first eight members of the homologous series of primary alcohols. TL measurements enable a direct study of these primary alcohols without adding any chromophore as a function of varying heat loads created via femtosecond laser pulses at 1560 nm. Convective heat transfer leads to the asymmetrical and reduced thermal gradient, which substantially weakens the TL signal. The inflection in the time profile of the TL signal of methanol at higher powers is attributed to the greater molecular convection in methanol compared to other samples. This inflection dies out with a decrease in laser power. Our results demonstrate that the convection is more prominent at higher laser powers in all samples, and it modifies the trend in the steady-state TL signal of different alcohols with pump laser power. Methanol also has the highest steady-state TL among the primary alcohol series at low laser powers. The maxima in the TL signal are shifted systematically from methanol to ethanol and then to propanol as the laser power increases. Semiempirical analysis of time-resolved TL signal by using the latest theoretical TL model enabled us to extract the coefficient of convective heat transfer in methanol at different laser powers. In addition to that, analysis of other members of alcohol series at the highest (7.3 mW) laser power shows that convection is more facile in short-chain alcohols compared to the long-chain alcohols.

    BibTeX: @article{singhalThermalLensStudy2019,
     title = {Thermal {{Lens Study}} of {{NIR Femtosecond Laser-Induced Convection}} in {{Alcohols}}},
     author = {Singhal, Sumit and Goswami, Debabrata},
     date = {2019-01-31},
     journaltitle = {ACS Omega},
     shortjournal = {ACS Omega},
     volume = {4},
     number = {1},
     pages = {1889--1896},
     issn = {2470-1343, 2470-1343},
     doi = {10/gf5mp4},
     url = {http://pubs.acs.org/doi/10.1021/acsomega.8b02956},
     urldate = {2019-08-01}
   }
   

2018

1. Interactions between Micro-Scale Oil Droplets in Aqueous Surfactant Solution Determined Using Optical Tweezers. A. Chen, S.-W. Li, F.-N. Sang, H.-B. Zeng, and J.-H. Xu, Journal of Colloid and Interface Science 532, 128–135 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: Hypothesis The stability of the emulsions is crucial, which relies on a well-developed understanding of dynamic interaction forces between single dispersed droplets. In the previous studies, many interests focus on the oil droplets of size range of 20–200 µm. However, emulsion droplets with diameter below 10 µm are rarely mentioned, which is the size scale of real emulsion droplets in various applications, such as toners, spacers for liquid crystal displays, and materials in biomedical and biochemical analysis. The micro-scale droplets have many differences on the deformation, internal pressure and hydrodynamic effects. It is necessary to understand the interaction mechanisms between two real size scales of oil droplets for guiding practical production and application. Experiments In this work, tetradecane was chosen as the model oil phase in all experiments. The interaction forces of two tetradecane droplets with the diameter of 5.0 µm in water in the presence of surfactant and salt solution were directly measured using optical tweezers. The force-distance curves were established, and the zeta potential of tetradecane droplets was studied using Zetasizer Nano ZSP. Findings The absolute value of zeta potential of tetradecane droplets was found to decrease with the increase of salt concentration and increase with the increase of surfactant concentration. The repulsive force between two tetradecane droplets was found to decrease with the increase of salt concentration because the electrostatic double-layer force was suppressed gradually with the increase of salt concentration. The “hydrodynamic suction” effect during the process of retraction becomes more pronounced due to the corresponding increase in the hydrodynamic force with the increase of the approaching velocity between the tetradecane droplets. Furthermore, we found the existing model for the measurement of large droplets by atomic force microscope (AFM) is invalid for the measurement of micro-scale droplets by optical tweezers. The deformation of colliding micro-scale droplets can be safely ignored, which is quite different from the large droplets. Our results provide a useful method to study the interaction forces between micro-scale emulsion droplets with pN force resolution, and gives a deep insight of the stabilization mechanism of real size scale of O/W emulsions. These findings have significant implications on the stability of emulsions in many food, cosmetics, medicine, and advanced materials.

    BibTeX: @article{chenInteractionsMicroscaleOil2018,
     title = {Interactions between Micro-Scale Oil Droplets in Aqueous Surfactant Solution Determined Using Optical Tweezers},
     author = {Chen, An and Li, Shao-Wei and Sang, Fu-Ning and Zeng, Hong-Bo and Xu, Jian-Hong},
     date = {2018-12-15},
     journaltitle = {Journal of Colloid and Interface Science},
     shortjournal = {Journal of Colloid and Interface Science},
     volume = {532},
     pages = {128--135},
     issn = {0021-9797},
     doi = {10/gf85zg},
     url = {http://www.sciencedirect.com/science/article/pii/S0021979718308804},
     urldate = {2019-10-01}
   }
   

2. Observing Ground State Vibrational Coherence and Excited State Relaxation Dynamics of a Cyanine Dye in Pure Solvents. D. K. Das, K. Makhal, and D. Goswami, Physical Chemistry Chemical Physics 20(19), 13400–13411 (2018) [PDF] [BibTeX]

    BibTeX: @article{dasObservingGroundState2018,
     title = {Observing Ground State Vibrational Coherence and Excited State Relaxation Dynamics of a Cyanine Dye in Pure Solvents},
     author = {Das, Dipak Kumar and Makhal, Krishnandu and Goswami, Debabrata},
     date = {2018},
     journaltitle = {Physical Chemistry Chemical Physics},
     volume = {20},
     number = {19},
     pages = {13400--13411},
     doi = {10/gf5mqz},
     url = {https://my.pcloud.com/publink/show?code=XZ1Axr7ZxiTGNbfEV1bmLPqho9PtQzSq3qUk},
     urldate = {2019-08-01}
   }
   

3. Solvent Effect on Multiple Emission and Ultrafast Dynamics of Higher Excited States. D. K. Das, K. Makhal, and D. Goswami, Chemical Physics Letters 706, 375–379 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: We present ultrafast-depopulation-dynamics of higher-lying-excited-states using femtosecond fluorescence up-conversion techniques for two near-infrared (NIR) tricarbocyanine dyes (IR144 and IR140) in primary alcohols. With visible excitation wavelengths, such dyes show two distinct emission-bands with large peak wavelength difference: one at the visible region: S2\,→ S0, and the other at NIR region: S1\,→ S0. We show that exact band-positions, intensities, and fluorescence-decay-timescales (τ) depend strongly on viscosity and polarity of solvents. Interestingly, though the faster component of τ increased for IR144 with increasing viscosity and chain-length of alcohols, the reverse was seen for IR140, indicating the possible formation of ion-pair of IR140 with alcohols.

    BibTeX: @article{dasSolventEffectMultiple2018,
     title = {Solvent Effect on Multiple Emission and Ultrafast Dynamics of Higher Excited States},
     author = {Das, Dipak Kumar and Makhal, Krishnandu and Goswami, Debabrata},
     date = {2018-08-16},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {706},
     pages = {375--379},
     issn = {0009-2614},
     doi = {10/gd3phb},
     url = {https://my.pcloud.com/publink/show?code=XZOAxr7ZeXIX0Ahn0DBrmUdo3wS0tyDPhbz7},
     urldate = {2019-08-01}
   }
   

4. Two Photon Spectroscopy Can Serve as a Marker of Protein Denaturation Pathway. D. K. Das, S. I. Islam, N. Samanta, Y. Yadav, D. Goswami, and R. K. Mitra, Journal of Fluorescence 28(3), 855–862 (2018) [PDF] [BibTeX]

    BibTeX: @article{dasTwoPhotonSpectroscopy2018,
     title = {Two {{Photon Spectroscopy Can Serve}} as a {{Marker}} of {{Protein Denaturation Pathway}}},
     author = {Das, Dipak Kumar and Islam, Sk Imadul and Samanta, Nirnay and Yadav, Yogendra and Goswami, Debabrata and Mitra, Rajib Kumar},
     date = {2018-05},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {28},
     number = {3},
     pages = {855--862},
     issn = {1053-0509, 1573-4994},
     doi = {10/gd2g84},
     url = {https://my.pcloud.com/publink/show?code=XZGNxr7ZDvT2qqOXdaJrTjbB8A2tB5nJ8kH7},
     urldate = {2019-08-01}
   }
   

5. Nobel Prize in Physics – 2018. D. Goswami, 9 (2018) [PDF] [BibTeX]

    BibTeX: @article{goswamiNobelPrizePhysics2018,
     title = {Nobel {{Prize}} in {{Physics}} – 2018},
     author = {Goswami, Debabrata},
     date = {2018},
     pages = {9},
     doi = {10/gf5mqq},
     url = {https://my.pcloud.com/publink/show?code=XZ3Gxr7Z2FLRny10VRFK6F48uNi7pYpeSmty}
   }
   

6. Spectrally Resolved Photon-Echo Spectroscopy of CdSe Quantum Dots at Far from Resonance Excitation Condition. D. Goswami, Journal of Chemical Sciences 130(10), 144 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: Spectrally resolved photon echo spectroscopy in the off-resonance condition is reported for the first time to study the coherence and population dynamics of CdSe quantum dots. In this case, the information related to the system dynamics can be inferred indirectly. This is especially useful when such dynamical information might be hidden under the absorption maxima of the sample. We observe that a substantial intensity of the photon echo signal was obtained in two different CdSe quantum dot samples (CdSe 610 and CdSe 640), which have absorption maxima at 620 nm and 590 nm, respectively. Due to the difference in sizes of these two quantum dots, a small change is observed in the molecular dynamics of these two quantum-dot samples. Specifically, the spectral diffusion of CdSe 640 occurs within the first 50 fs, whereas that for CdSe 610 occurs at about 100 fs timescale. The integrated plots of the photon echo signal, as a function of population time, result in two decay constants. The faster among the two decay components is pulse width limited and is in between 30 and 40 fs at different fixed coherence times for both samples. The slower decay component for the CdSe 610 sample is found to be in the range of 75–85 fs, while that for CdSe 640, it is between 82 and 92 fs at different fixed coherence times.

    BibTeX: @article{goswamiSpectrallyResolvedPhotonecho2018,
     title = {Spectrally Resolved Photon-Echo Spectroscopy of {{CdSe}} Quantum Dots at Far from Resonance Excitation Condition},
     author = {Goswami, Debabrata},
     date = {2018-10},
     journaltitle = {Journal of Chemical Sciences},
     shortjournal = {J Chem Sci},
     volume = {130},
     number = {10},
     pages = {144},
     issn = {0974-3626, 0973-7103},
     doi = {10/gfc5tj},
     url = {https://my.pcloud.com/publink/show?code=XZrGxr7ZCXB5pJHxB4VOKIzAjjEBcmLbB6Gk},
     urldate = {2019-08-01}
   }
   

7. White Light Induced E/Z-Photoisomerization of Diphenylamine-Tethered Fluorescent Stilbene Derivatives: Synthesis, Photophysical, and Electrochemical Investigation. S. Mishra, P. Awasthi, J. Singh, R. K. Gupta, V. Singh, R. Kant, R. Jeet, D. Goswami, and A. Goel, The Journal of Organic Chemistry 83(7), 3669–3678 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: A facile synthesis and detailed photophysical investigation of E/Z-isomerization of fluorescent diphenylamine tethered stilbene derivatives (DPASs) under white light exposure have been carried out to understand the effect on fluorescence, electrochemical properties, and photostability under various activation/deactivation pathways. In solution state, in the dark, the E-isomer of DPASs (6a−d) exhibited high fluorescence quantum yields (Φfl ≈ 53% to 60% in DMSO). However, on white light exposure, 1H NMR and HPLC studies revealed that pure E-isomer of the DPAS 6a (∼9.5 mM) started converting into its Z-form by photoisomerization until it reaches to nearly equilibrium. At low concentrations (∼10 μM), the absorption band of the pure Eisomer in the range of 350−450 nm gradually decreased to adopt Z-conformation 6a′ until a photostationary state was reached. The structure of the E-isomer 6a was unequivocally confirmed by X-ray diffraction analysis. The synthesized DPAS compounds 6a−d possessed positive solvatochromic properties, two photon absorption properties, and good thermal stability. The electrochemical investigations using DPASs showed reversible oxidation resulting in formation of a stable radical cation. Owing to useful photophysical, electrochemical and thermal properties, these DPAS derivatives are suitable for their application in biomedical imaging as well as in fabrication of electroluminescent materials.

    BibTeX: @article{mishraWhiteLightInduced2018,
     title = {White {{Light Induced E}}/{{Z-Photoisomerization}} of {{Diphenylamine-Tethered Fluorescent Stilbene Derivatives}}: {{Synthesis}}, {{Photophysical}}, and {{Electrochemical Investigation}}},
     shorttitle = {White {{Light Induced E}}/{{Z-Photoisomerization}} of {{Diphenylamine-Tethered Fluorescent Stilbene Derivatives}}},
     author = {Mishra, Shachi and Awasthi, Pallavi and Singh, Jagriti and Gupta, Rahul Kumar and Singh, Vikram and Kant, Ruchir and Jeet, Ram and Goswami, Debabrata and Goel, Atul},
     date = {2018-04-06},
     journaltitle = {The Journal of Organic Chemistry},
     shortjournal = {J. Org. Chem.},
     volume = {83},
     number = {7},
     pages = {3669--3678},
     issn = {0022-3263, 1520-6904},
     doi = {10/gc6tzq},
     url = {http://pubs.acs.org/doi/10.1021/acs.joc.8b00033},
     urldate = {2019-08-01}
   }
   

8. On-the-Fly Calibrated Measure and Remote Control of Temperature and Viscosity at Nanoscale. D. Mondal, S. N. Bandyopadhyay, P. Mathur, and D. Goswami, ACS Omega 3(9), 12304–12311 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: A novel on-the-f ly calibration method of optical tweezers is presented, which enables in situ control and measure of absolute temperature and viscosity at nanoscale dimensions. Such noncontact measurement and control at the nanoscale are challenging as the present techniques only provide off-line measurements that do not provide absolute values. Additionally, some of the present methods have a low spatial resolution. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The femtosecond optical tweezers (FOTs) use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Such finer temperature gradients are due to the additional nonlinear optical (NLO) phenomena occurring only at the nanoscale focal plane of the FOTs. Because NLO processes are laser peak power-dependent, they promote an effective study of physical properties occurring only at the focal plane. Using FOTs at optically benign near-infrared wavelengths, we demonstrate microrheological control and measurement in water by adding a highly absorbing yet low fluorescent dye (IR780).

    BibTeX: @article{mondalOntheFlyCalibratedMeasure2018,
     title = {On-the-{{Fly Calibrated Measure}} and {{Remote Control}} of {{Temperature}} and {{Viscosity}} at {{Nanoscale}}},
     author = {Mondal, Dipankar and Bandyopadhyay, Soumendra Nath and Mathur, Paresh and Goswami, Debabrata},
     date = {2018-09-30},
     journaltitle = {ACS Omega},
     shortjournal = {ACS Omega},
     volume = {3},
     number = {9},
     pages = {12304--12311},
     issn = {2470-1343, 2470-1343},
     doi = {10/gff5s6},
     url = {http://pubs.acs.org/doi/10.1021/acsomega.8b01572},
     urldate = {2019-08-01}
   }
   

9. Deciphering Micro-Polarity inside the Endoplasmic Reticulum Using a Two-Photon Active Solvatofluorochromic Probe. K. Pal, I. Samanta, R. Kumar Gupta, D. Goswami, and A. Lal Koner, Chemical Communications 54(75), 10590–10593 (2018) [PDF] [BibTeX]

    BibTeX: @article{palDecipheringMicropolarityEndoplasmic2018,
     title = {Deciphering Micro-Polarity inside the Endoplasmic Reticulum Using a Two-Photon Active Solvatofluorochromic Probe},
     author = {Pal, Kaushik and Samanta, Indranil and Kumar~Gupta, Rahul and Goswami, Debabrata and Lal~Koner, Apurba},
     date = {2018},
     journaltitle = {Chemical Communications},
     volume = {54},
     number = {75},
     pages = {10590--10593},
     doi = {10/gf5mqx},
     url = {https://pubs.rsc.org/en/content/articlelanding/2018/cc/c8cc03962c},
     urldate = {2019-08-01}
   }
   

2017

1. Meet OSA’s 2017 Fellows. K. Apter, M. Smith, and Z. Epps, Optics and Photonics News 28(2), 38–47 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: The 96 members of the 2017 class of OSA Fellow Members will be recognized at conferences throughout the year for scientific, engineering, educational and technological contributions, as well as service and business leadership.

    BibTeX: @article{apterMeetOSA20172017,
     title = {Meet {{OSA}}’s 2017 {{Fellows}}},
     author = {Apter, Kari and Smith, Meredith and Epps, Zsanai},
     date = {2017-02-01},
     journaltitle = {Optics and Photonics News},
     shortjournal = {Optics \& Photonics News, OPN},
     volume = {28},
     number = {2},
     pages = {38--47},
     issn = {1541-3721},
     doi = {10/gf5mrj},
     url = {https://my.pcloud.com/publink/show?code=XZqaxr7ZmnVNxAn4Y4mRbGS3d4A7FjmCWEv7},
     urldate = {2019-08-01}
   }
   

2. Two-Dimensional Imaging of a Second-Order Nonlinear Optical Process. I. Bhattacharyya and D. Goswami, Current Science 112(04), 830 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: Spatiotemporal imaging of sum-frequency generation process through second-order nonlinear optical interaction in a nonlinear crystal under femtosecond pulsed illumination is presented. Two focal points in the spatial dimension that result from use of widely separated wavelengths (780 and 1560 nm) including their appropriate intensity ratios are captured accurately, emphasizing the sensitivity and robustness of this detection scheme. Most importantly, crosscorrelation width that is used as characteristic measure from such techniques remains constant at the two focal points. However, this highlights the critical role of nonlinear crystal position along beam propagation axis during such collinear intensity cross-correlation measurements involving different wavelengths.

    BibTeX: @article{bhattacharyyaTwoDimensionalImagingSecondOrder2017,
     title = {Two-{{Dimensional Imaging}} of a {{Second-Order Nonlinear Optical Process}}},
     author = {Bhattacharyya, Indrajit and Goswami, Debabrata},
     date = {2017-02-01},
     journaltitle = {Current Science},
     volume = {112},
     number = {04},
     pages = {830},
     issn = {0011-3891},
     doi = {10/f92q98},
     url = {http://pc.cd/mxLctalK},
     urldate = {2019-08-01}
   }
   

3. Extracting Third Order Optical Nonlinearities of Mn(III)-Phthalocyanine Chloride Using High Repetition Rate Femtosecond Pulses. K. Makhal, P. Mathur, S. Maurya, and D. Goswami, Journal of Applied Physics 121(5), 053103 (2017) [PDF] [BibTeX]

    BibTeX: @article{makhalExtractingThirdOrder2017,
     title = {Extracting Third Order Optical Nonlinearities of {{Mn}}({{III}})-{{Phthalocyanine}} Chloride Using High Repetition Rate Femtosecond Pulses},
     author = {Makhal, Krishnandu and Mathur, Paresh and Maurya, Sidharth and Goswami, Debabrata},
     date = {2017-02-06},
     journaltitle = {Journal of Applied Physics},
     shortjournal = {Journal of Applied Physics},
     volume = {121},
     number = {5},
     pages = {053103},
     issn = {0021-8979},
     doi = {10/gf5mrh},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.4974966},
     urldate = {2019-08-01}
   }
   

4. pH Effect on Two-Photon Cross Section of Highly Fluorescent Dyes Using Femtosecond Two-Photon Induced Fluorescence. K. Makhal and D. Goswami, Journal of Fluorescence 27(1), 339–356 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: Effect of solution pH on two-photon absorption cross-section of highly fluorescent Coumarin and Rhodamine dyes with high repetition rate femtosecond laser pulses at 780 nm is presented using two-photon induced fluorescence technique. A correspondence in the measured two-photon and single-photon cross-section values is seen when the pH changes from acidic to basic conditions (pH = 2–10) for solutions in 1:1 water-ethanol binary mixture. By plotting changes in the single-photon and two-photon fluorescence in this pH range, the excited state pKa values are found. The ground state pKa values are also affected by the protonation deprotonation equilibrium as a result of variation in pH from acidic to basic, which are characterized by changes in absorbance spectra. Most of these single-photon and two-photon induced fluorescence spectra show characteristic blue shifts. Different fluorescence quantum yields calculated at each pH reflect a change in structure corresponding to their associated properties as a result of acid base equilibrium.

    BibTeX: @article{makhalPHEffectTwoPhoton2017,
     title = {{{pH Effect}} on {{Two-Photon Cross Section}} of {{Highly Fluorescent Dyes Using Femtosecond Two-Photon Induced Fluorescence}}},
     author = {Makhal, Krishnandu and Goswami, Debabrata},
     date = {2017-01-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {27},
     number = {1},
     pages = {339--356},
     issn = {1573-4994},
     doi = {10/f9rpw6},
     url = {https://doi.org/10.1007/s10895-016-1963-4},
     urldate = {2019-08-01}
   }
   

5. Concentration Dependent Approach for Accurate Determination of Two-Photon Absorption Cross-Section of Fluorescent Dye Molecule. S. K. Maurya, C. Dutta, and D. Goswami, Journal of Fluorescence 27(4), 1399–1403 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: We have investigated the concentration dependent of two-photon induced fluorescence (TPIF) in methanolic solution of Rhodamine 6G and Rhodamine B dye using 120 fs laser pulses at 780 nm, 76 MHz repetition rate. TPIF study of these dyes was compared with their respective one photon fluorescence intensity. We have shown the effect of chopper on TPIF intensity from Rhodamine dyes, which have shown direct influence on the determined TPA Cross section of these dyes.

    BibTeX: @article{mauryaConcentrationDependentApproach2017,
     title = {Concentration {{Dependent Approach}} for {{Accurate Determination}} of {{Two-Photon Absorption Cross-Section}} of {{Fluorescent}} Dye {{Molecule}}},
     author = {Maurya, Sandeep Kumar and Dutta, Chayan and Goswami, Debabrata},
     date = {2017-07-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {27},
     number = {4},
     pages = {1399--1403},
     issn = {1573-4994},
     doi = {10/gf5mq7},
     url = {https://doi.org/10.1007/s10895-017-2076-4},
     urldate = {2019-08-01}
   }
   

6. Measurement of Pure Optical Nonlinearity in Carbon Disulfide with a High-Repetition-Rate Femtosecond Laser. S. Singhal, S. Dinda, and D. Goswami, Applied Optics 56(3), 644 (2017) [PDF] [BibTeX]

    BibTeX: @article{singhalMeasurementPureOptical2017,
     title = {Measurement of Pure Optical Nonlinearity in Carbon Disulfide with a High-Repetition-Rate Femtosecond Laser},
     author = {Singhal, Sumit and Dinda, Sirshendu and Goswami, Debabrata},
     date = {2017-01-20},
     journaltitle = {Applied Optics},
     shortjournal = {Appl. Opt.},
     volume = {56},
     number = {3},
     pages = {644},
     issn = {0003-6935, 1539-4522},
     doi = {10/gf5mrm},
     url = {https://www.osapublishing.org/abstract.cfm?URI=ao-56-3-644},
     urldate = {2019-08-01}
   }
   

7. A Dual-Signaling Ferrocene-Pyrene Dyad: Triple-Mode Recognition of the Cu(II) Ions in Aqueous Medium. M. A. Wani, M. D. Pandey, R. Pandey, S. K. Maurya, and D. Goswami, Journal of Fluorescence 27(6), 2279–2286 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: We report a structure of ferrocene-pyrene conjugate (1) comprising electro and photo-active dual-signaling units. In particular, 1 upon interaction with Cu(II), displays selectively one-photon fluorescence quenching, but it shows two-photon absorption (TPA) cross-section 1230 GM (at 780 nm). Further, 1 displayed two irreversible oxidative waves at 0.39 V and 0.80 V (vs Ag/AgCl), in the electrochemical analysis which upon addition of Cu2+, led to the negative potential shift in both the oxidative waves to appear at 0.25 V and 0.68 V. The triple mode changes in presence of Cu(II) suggesting the possible application of 1 for the detection of Cu(II) in aqueous media. Open image in new window Graphical Abstract

    BibTeX: @article{waniDualSignalingFerrocenePyreneDyad2017,
     title = {A {{Dual-Signaling Ferrocene-Pyrene Dyad}}: {{Triple-Mode Recognition}} of the {{Cu}}({{II}}) {{Ions}} in {{Aqueous Medium}}},
     shorttitle = {A {{Dual-Signaling Ferrocene-Pyrene Dyad}}},
     author = {Wani, Manzoor Ahmad and Pandey, Mrituanjay D. and Pandey, Rampal and Maurya, Sandeep Kumar and Goswami, Debabrata},
     date = {2017-11-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {27},
     number = {6},
     pages = {2279--2286},
     issn = {1573-4994},
     doi = {10/gch5h7},
     url = {https://doi.org/10.1007/s10895-017-2169-0},
     urldate = {2019-08-01}
   }
   

2016

1. Spatiotemporal Control of Degenerate Multiphoton Fluorescence Microscopy with Delay-Tunable Femtosecond Pulse Pairs. D. Das, I. Bhattacharyya, and D. Goswami, Chemical Physics Letters 657, 72–77 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Selective excitation of a particular fluorophore in an ensemble of different fluorophores with overlapping fluorescence spectra is shown to be dependent on the time delay of femtosecond pulse pairs in multiphoton fluorescence microscopy. In particular, the two-photon fluorescence behavior of the Texas Red and DAPI dye pair inside Bovine Pulmonary Artery Endothelial (BPAE) cells depends strongly on the center wavelength of the laser, as well as the delay between two identical laser pulses in one-color femtosecond pulse-pair excitation scheme. Thus, we present a novel design concept using pairs of femtosecond pulses at different central wavelengths and tunable pulse separations for controlling the image contrast between two spatially and spectrally overlapping fluorophores. This femtosecond pulse-pair technique is unique in utilizing the variation of dye dynamics inside biological cells as a contrast mode in microscopy of different fluorophores.

    BibTeX: @article{dasSpatiotemporalControlDegenerate2016,
     title = {Spatiotemporal Control of Degenerate Multiphoton Fluorescence Microscopy with Delay-Tunable Femtosecond Pulse Pairs},
     author = {Das, Dhiman and Bhattacharyya, Indrajit and Goswami, Debabrata},
     date = {2016-07-16},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {657},
     pages = {72--77},
     issn = {0009-2614},
     doi = {10/f84rwd},
     url = {https://my.pcloud.com/publink/show?code=XZ1Axr7ZxiTGNbfEV1bmLPqho9PtQzSq3qUk},
     urldate = {2019-08-01}
   }
   

2. On the Interferometric Coherent Structures in Femtosecond Supercontinuum Generation. S. Dinda, S. N. Bandyopadhyay, and D. Goswami, Applied Physics B 122(5), 148 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: We report structured interferometric features in femtosecond supercontinuum generation (FSG) with incident laser powers that are near threshold for FSG. We argue that near threshold, these structures arise from the coherent superposition of pulses that are split initially into two daughter pulses during FSG process. Increase in the input pulse energy generates multiple daughter fragments in the temporal domain to an extent that correlated interference structures are not measurable.

    BibTeX: @article{dindaInterferometricCoherentStructures2016,
     title = {On the Interferometric Coherent Structures in Femtosecond Supercontinuum Generation},
     author = {Dinda, Sirshendu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2016-05-11},
     journaltitle = {Applied Physics B},
     shortjournal = {Appl. Phys. B},
     volume = {122},
     number = {5},
     pages = {148},
     issn = {1432-0649},
     doi = {10/gf5mr5},
     url = {https://my.pcloud.com/publink/show?code=XZfaxr7ZhXTWojTzmcfBOA16JDESUyR5fRWV},
     urldate = {2019-08-01}
   }
   

3. Optical Trapping Dynamics of a Single Polystyrene Sphere: Continuous Wave versus Femtosecond Lasers. T.-H. Liu, W.-Y. Chiang, A. Usman, and H. Masuhara, The Journal of Physical Chemistry C 120(4), 2392–2399 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Understanding of optical trapping dynamics of a single particle in the trapping site is important to develop its optical manipulation for molecular assembly and chemical application. For micrometer-sized Mie particles, similar trapping efficiency of the conventional continuous wave (cw) laser or high-repetition-rate femtosecond (fs) laser pulse train has been established [Dholakia et al., Opt. Express 2010, 18, 7554–7568], in contrast to higher efficiency of the laser pulses to trap dielectric Rayleigh particles. To further explore and clarify the switching phenomena of optical trapping efficiency with cw laser and fs laser pulse and to elucidate its nature, we study the immobilization dynamics of a single polystyrene sphere with 500 nm in diameter (which is comparable to focal beam size) in shallow potential well. By observing trapping events and immobilization time of the particle with a size in Lorenz–Mie regime, distinct from well-known Rayleigh particle and ray optics approximations, we found that immobilization time is only linearly related to the incident laser power ≤40 mW, and at higher laser powers cw laser is more efficient than fs laser pulses to immobilize the particle. This finding means that the dynamics of the particle in this size region is still affected by the strong transient force fields induced by high-repetition-rate ultrashort pulse train as usually observed for Rayleigh particles. This may provide an understanding that the dynamics of the target particle in the trapping site is size- and laser mode-dependent.

    BibTeX: @article{liuOpticalTrappingDynamics2016,
     title = {Optical {{Trapping Dynamics}} of a {{Single Polystyrene Sphere}}: {{Continuous Wave}} versus {{Femtosecond Lasers}}},
     shorttitle = {Optical {{Trapping Dynamics}} of a {{Single Polystyrene Sphere}}},
     author = {Liu, Tsung-Han and Chiang, Wei-Yi and Usman, Anwar and Masuhara, Hiroshi},
     date = {2016-02-04},
     journaltitle = {The Journal of Physical Chemistry C},
     shortjournal = {J. Phys. Chem. C},
     volume = {120},
     number = {4},
     pages = {2392--2399},
     issn = {1932-7447},
     doi = {10/gf85zr},
     url = {https://doi.org/10.1021/acs.jpcc.5b09146},
     urldate = {2019-10-01}
   }
   

4. Third-Order Nonlinear Optical Response and Ultrafast Dynamics of Tetraoxa[22]Porphyrin(2.1.2.1)s. K. Makhal, S. Arora, P. Kaur, D. Goswami, and K. Singh, Journal of Materials Chemistry C 4(40), 9445–9453 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast dynamics and third-order nonlinear optical studies of tetraoxa[22]porphyrin(2.1.2.1)s are reported using a single beam Z-scan technique with femtosecond (fs) and nanosecond (ns) pulses at respective near-IR and visible wavelengths. Excited state absorption mediated reverse saturable absorption was observed at 527 nm while two-photon absorption was observed at 800 nm. High nonlinear refractive index coefficient (γ) and nonlinear absorption coefficient (β) values and the fast response times were attributed to the availability of polarizable π-electrons of the cyclic conjugated aromatic porphyrin framework. Our proposed mechanism of third-order nonlinearity was verified using ultrafast transient absorption spectroscopy. With the observed fast electronic nonlinearities the studied molecules are potential candidates for use as optical limiters.

    BibTeX: @article{makhalThirdorderNonlinearOptical2016,
     title = {Third-Order Nonlinear Optical Response and Ultrafast Dynamics of Tetraoxa[22]Porphyrin(2.1.2.1)s},
     author = {Makhal, Krishnandu and Arora, Shafali and Kaur, Paramjit and Goswami, Debabrata and Singh, Kamaljit},
     date = {2016},
     journaltitle = {Journal of Materials Chemistry C},
     volume = {4},
     number = {40},
     pages = {9445--9453},
     doi = {10/gf5mr7},
     url = {https://pubs.rsc.org/en/content/articlelanding/2016/tc/c6tc03239g},
     urldate = {2019-08-01}
   }
   

5. Investigating Two-Photon-Induced Fluorescence in Rhodamine-6G in Presence of Cetyl-Trimethyl-Ammonium-Bromide. S. K. Maurya, D. Yadav, and D. Goswami, Journal of Fluorescence 26(5), 1573–1577 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: We investigate the effect of cetyl-trimethyl-ammonium-bromides (CTAB) concentration on the fluorescence of Rhodamine-6G in water. This spectroscopic study of Rhodamine-6G in presence of CTAB was performed using two-photon-induced-fluorescence at 780 nm wavelength using high repetition rate femtosecond laser pulses. We report an increment of ∼10 % in the fluorescence in accordance with ∼12 % enhancement in the absorption intensity of the dye molecule around the critical micellar concentration. We discuss the possible mechanism for the enhancement in the two-photon fluorescence intensity and the importance of critical micellar concentration.

    BibTeX: @article{mauryaInvestigatingTwoPhotonInducedFluorescence2016,
     title = {Investigating {{Two-Photon-Induced Fluorescence}} in {{Rhodamine-6G}} in {{Presence}} of {{Cetyl-Trimethyl-Ammonium-Bromide}}},
     author = {Maurya, Sandeep Kumar and Yadav, Dheerendra and Goswami, Debabrata},
     date = {2016-09-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {26},
     number = {5},
     pages = {1573--1577},
     issn = {1573-4994},
     doi = {10/f82q4x},
     url = {https://doi.org/10.1007/s10895-016-1841-0},
     urldate = {2019-08-01}
   }
   

6. Probing Intermolecular Interactions in Binary Liquid Mixtures Using Femtosecond Laser-Induced Self-Defocusing. S. K. Maurya, D. Das, and D. Goswami, Applied Spectroscopy 70(10), 1655–1661 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Photothermal behavior of binary liquid mixtures has been studied using a high repetition rate (HRR) Z-scan technique with femtosecond laser pulses. Changes in the peak–valley difference in transmittance (ΔTP–V) for closed aperture Z-scan experiments are indicative of thermal effects induced by HRR femtosecond laser pulses. We show such indicative results can have a far-reaching impact on molecular properties and intermolecular interactions in binary liquid mixtures. Spectroscopic parameters derived from this experimental technique show that the combined effect of physical and molecular properties of the constituent binary liquids can be related to the components of the binary liquid.

    BibTeX: @article{mauryaProbingIntermolecularInteractions2016,
     title = {Probing {{Intermolecular Interactions}} in {{Binary Liquid Mixtures Using Femtosecond Laser-Induced Self-Defocusing}}},
     author = {Maurya, Sandeep Kumar and Das, Dhiman and Goswami, Debabrata},
     date = {2016-10-01},
     journaltitle = {Applied Spectroscopy},
     shortjournal = {Appl Spectrosc},
     volume = {70},
     number = {10},
     pages = {1655--1661},
     issn = {0003-7028},
     doi = {10/gf5mrx},
     url = {https://doi.org/10.1177/0003702816643547},
     urldate = {2019-08-01}
   }
   

7. Controlling and Tracking of Colloidal Nanostructures through Two-Photon Fluorescence. D. Mondal and D. Goswami, Methods and Applications in Fluorescence 4(4), 044004 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Multiphoton absorbing dye-coated trapped spherical bead at the focal plane of femtosecond optical tweezers shows nonlinear optical (NLO) phenomena. One such NLO process of two-photon fluorescence (TPF) has been used for the background-free imaging of a femtosecond laser-trapping event. Due to the high peak powers of femtosecond laser pulses with low average powers, it is possible to not only trap single nanospheres, but encourage optically directed self-assembly. The TPF signatures of trapped particles show evidence of such a directed self-assembly process which, in turn, can provide information about the structural dynamics during the process of cluster formation. We are able to trap and characterize structure and dynamics in 3D until pentamer formation from the decay characteristics of trapping at the focal plane.

    BibTeX: @article{mondalControllingTrackingColloidal2016,
     title = {Controlling and Tracking of Colloidal Nanostructures through Two-Photon Fluorescence},
     author = {Mondal, Dipankar and Goswami, Debabrata},
     date = {2016-10-07},
     journaltitle = {Methods and Applications in Fluorescence},
     shortjournal = {Methods Appl. Fluoresc.},
     volume = {4},
     number = {4},
     pages = {044004},
     issn = {2050-6120},
     doi = {10/gf5mrw},
     url = {http://stacks.iop.org/2050-6120/4/i=4/a=044004?key=crossref.b299c380a1fd88f37b79e579221d3e7a},
     urldate = {2019-08-01}
   }
   

8. Precise Control and Measurement of Temperature with Femtosecond Optical Tweezers. D. Mondal and D. Goswami, Biophysical Journal 110(3), 500a (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Optical traps have often been used for physical manipulation and transport within liquids for studying bio-systems. In this connection, though a lot of work has focused on the property of the trapped particle, there is little effort on utilizing the effect of the trapping environment. Here we demonstrate a novel method for exploiting the effect of trapping environment in observing the temperature rise in liquids directly at the vicinity of an optical trap center. Our approach utilizes the photo-thermal effect at micro-volume dimension to measure temperature, which could eventually be extended to in-vivo conditions. Our two-color experiment is a unique combination of a non-heating femtosecond trapping laser at 780 nm, which is coupled to a femtosecond infrared heating laser at 1560 nm. Femtosecond pulsed laser heating is much more effective than the traditional continuous-wave laser, which increases the sensitivity of our measurements. The heating laser precisely controls temperature at the focal volume of the trap center using low powers at high repetition rate. The changed values of corner frequency of the optical trap due to this local heating is recognized from its power spectra. The solvent having hydroxyl group is very sensitive to 1560 nm laser due to non-radiative relaxation from their higher excited state. Since most bio-systems contain hydroxyl group, they would be highly responsive to our heating laser, while our trapping laser is highly transparent for such systems. Our method could be used to specifically heat a particular cell to evaluate its faster cell division and also can be utilized for the possible phototherapy of cancer cells. The advantage of this technique over the conventional phototherapy is that this is highly localized due to focusing through high numerical aperture resulting in a high gradient of temperature.

    BibTeX: @article{mondalPreciseControlMeasurement2016,
     title = {Precise {{Control}} and {{Measurement}} of {{Temperature}} with {{Femtosecond Optical Tweezers}}},
     author = {Mondal, Dipankar and Goswami, Debabrata},
     date = {2016-02},
     journaltitle = {Biophysical Journal},
     shortjournal = {Biophysical Journal},
     volume = {110},
     number = {3},
     pages = {500a},
     issn = {00063495},
     doi = {10/gf5mr6},
     url = {https://linkinghub.elsevier.com/retrieve/pii/S0006349515038564},
     urldate = {2019-08-01}
   }
   

9. Precise Control and Measurement of Solid–Liquid Interfacial Temperature and Viscosity Using Dual-Beam Femtosecond Optical Tweezers in the Condensed Phase. D. Mondal, P. Mathur, and D. Goswami, Physical Chemistry Chemical Physics 18(37), 25823–25830 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: We present a novel method of microrheology based on femtosecond optical tweezers, which in turn enables us to directly measure and control in situ temperature at microscale volumes at the solid–liquid interface. A noninvasive pulsed 780 nm trapped bead spontaneously responds to changes in its environment induced by a co-propagating 1560 nm pulsed laser due to mutual energy transfer between the solvent molecules and the trapped bead. Strong absorption of the hydroxyl group by the 1560 nm laser creates local heating in individual and binary mixtures of water and alcohols. “Hot Brownian motion” of the trapped polystyrene bead is reflected in the corner frequency deduced from the power spectrum. Changes in corner frequency values enable us to calculate the viscosity as well as temperature at the solid–liquid interface. We show that these experimental results can also be theoretically ratified.

    BibTeX: @article{mondalPreciseControlMeasurement2016a,
     title = {Precise Control and Measurement of Solid–Liquid Interfacial Temperature and Viscosity Using Dual-Beam Femtosecond Optical Tweezers in the Condensed Phase},
     author = {Mondal, Dipankar and Mathur, Paresh and Goswami, Debabrata},
     date = {2016},
     journaltitle = {Physical Chemistry Chemical Physics},
     volume = {18},
     number = {37},
     pages = {25823--25830},
     doi = {10/gf5mr8},
     url = {https://pubs.rsc.org/en/content/articlelanding/2016/cp/c6cp03093a},
     urldate = {2019-08-01}
   }
   

10. Sensitive in Situ Nanothermometer Using Femtosecond Optical Tweezers. D. Mondal and D. Goswami, Journal of Nanophotonics 10(2), 026013 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: We report the rise in temperature in various liquid media adjacent to a trapped bead. A nonheating laser at 780 nm has been used to optically trap a 500-nm radius polystyrene bead, while a simultaneous irradiation with a copropagating 1560-nm high-repetition-rate femtosecond laser led to temperature rise in various trapping media. Vibrational combination band of the hydroxyl group in the trapping media resulted in high absorption of 1560-nm laser. This, in turn, gave us control over the trapping media temperature at the focus of the optical trap.

     BibTeX: @article{mondalSensitiveSituNanothermometer2016,
      title = {Sensitive in Situ Nanothermometer Using Femtosecond Optical Tweezers},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-05},
      journaltitle = {Journal of Nanophotonics},
      shortjournal = {JNP},
      volume = {10},
      number = {2},
      pages = {026013},
      issn = {1934-2608, 1934-2608},
      doi = {10/f832c9},
      url = {https://www.spiedigitallibrary.org/journals/Journal-of-Nanophotonics/volume-10/issue-2/026013/----Custom-HTML----Sensitive/10.1117/1.JNP.10.026013.short},
      urldate = {2019-08-01}
    }
    

11. Two-Photon Absorption Cross Sections in a Dual-Signaling Ferrocene Pyrene Conjugate. M. D. Pandey, S. K. Maurya, D. Goswami, M. A. Wani, and R. Pandey, 2 (2016) [Abstract] [BibTeX]

    Abstract: We report a ferrocene-pyrene conjugate (1) as an electroactive and photoactive signaling units. Copper mediated system selectively shows highly two-photon absorption activity 1230 GM at 780 nm, in contrast to strong one-photon fluorescence quenching.

     BibTeX: @article{pandeyTwophotonAbsorptionCross2016,
      title = {Two-Photon Absorption Cross Sections in a Dual-Signaling Ferrocene Pyrene Conjugate},
      author = {Pandey, Mrituanjay D and Maurya, Sandeep Kumar and Goswami, Debabrata and Wani, Manzoor Ahmad and Pandey, Rampal},
      date = {2016},
      pages = {2},
      doi = {10/gf8pjt}
    }
    

12. Structure and Dynamics of Optically Directed Self-Assembly of Nanoparticles. D. Roy, D. Mondal, and D. Goswami, Scientific Reports 6, 23318 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: Self-assembly of nanoparticles leading to the formation of colloidal clusters often serves as the representative analogue for understanding molecular assembly. Unravelling the in situ structure and dynamics of such clusters in liquid suspensions is highly challenging. Presently colloidal clusters are first isolated from their generating environment and then their structures are probed by light scattering methods. In order to measure the in situ structure and dynamics of colloidal clusters, we have generated them using the high-repetition-rate femtosecond laser pulse optical tweezer. Since the constituent of our dimer, trimer or tetramer clusters are 250 nm radius two-photon resonant fluorophore coated nanospheres under the optical trap, they inherently produce Two-Photon Fluorescence, which undergo intra-nanosphere Fluorescence Energy Transfer. This unique energy transfer signature, in turn, enables us to visualize structures and orientations of these colloidal clusters during the process of their formation and subsequent dynamics in a liquid suspension. We also show that due to shape-birefringence, orientation and structural control of these colloidal clusters are possible as the polarization of the trapping laser is changed from linear to circular. We thus report important progress in sampling the smallest possible aggregates of nanoparticles, dimers, trimers or tetramers, formed early in the self-assembly process.

     BibTeX: @article{royStructureDynamicsOptically2016,
      title = {Structure and Dynamics of Optically Directed Self-Assembly of Nanoparticles},
      author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-03-23},
      journaltitle = {Scientific Reports},
      volume = {6},
      pages = {23318},
      issn = {2045-2322},
      doi = {10/f8fjqk},
      url = {https://www.nature.com/articles/srep23318},
      urldate = {2019-08-01}
    }
    

13. Two-Photon Fluorescence Tracking of Colloidal Clusters. D. Roy, D. Mondal, and D. Goswami, Journal of Fluorescence 26(4), 1271–1277 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: In situ dynamics of colloidal cluster formation from nanoparticles is yet to be addressed. Using two-photon fluorescence (TPF) that has been amply used for single particle tracking, we demonstrate in situ measurement of effective three-dimensional optical trap stiffness of nanoparticles and their aggregates without using any position sensitive detector. Optical trap stiffness is an essential measure of the strength of an optical trap. TPF is a zero-background detection scheme and has excellent signal-to-noise-ratio, which can be easily extended to study the formation of colloidal cluster of nanospheres in the optical trapping regime. TPF tracking can successfully distinguish colloidal cluster from its monomer.

     BibTeX: @article{royTwoPhotonFluorescenceTracking2016,
      title = {Two-{{Photon Fluorescence Tracking}} of {{Colloidal Clusters}}},
      author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-07-01},
      journaltitle = {Journal of Fluorescence},
      shortjournal = {J Fluoresc},
      volume = {26},
      number = {4},
      pages = {1271--1277},
      issn = {1573-4994},
      doi = {10/f82fs3},
      url = {https://doi.org/10.1007/s10895-016-1814-3},
      urldate = {2019-08-01}
    }
    

14. Nonlinear Absorption in Tetrathia[22]Porphyrin(2.1.2.1)s: Visualizing Strong Reverse Saturable Absorption at Non-Resonant Excitation. K. Singh, S. Arora, K. Makhal, P. Kaur, and D. Goswami, RSC Advances 6(27), 22659–22663 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: The nonlinear optical absorption properties of three meso-substituted aromatic, neutral tetrathia[22]porphyrin(2.1.2.1) compounds were investigated using an open aperture Z-scan technique at 527 nm with a pulse width of 100 ns in dichloromethane. The responses obtained were accounted for by invoking reverse saturable absorption arising due to strong excited state absorption. Both ground and excited state absorption cross-sections are reported, which follow the same trend as the respective structural parameters.

     BibTeX: @article{singhNonlinearAbsorptionTetrathia2016,
      title = {Nonlinear Absorption in Tetrathia[22]Porphyrin(2.1.2.1)s: Visualizing Strong Reverse Saturable Absorption at Non-Resonant Excitation},
      shorttitle = {Nonlinear Absorption in Tetrathia[22]Porphyrin(2.1.2.1)s},
      author = {Singh, Kamaljit and Arora, Shafali and Makhal, Krishnandu and Kaur, Paramjit and Goswami, Debabrata},
      date = {2016},
      journaltitle = {RSC Advances},
      volume = {6},
      number = {27},
      pages = {22659--22663},
      doi = {10/gf5mr9},
      url = {https://pubs.rsc.org/en/content/articlelanding/2016/ra/c5ra22861a},
      urldate = {2019-08-01}
    }
    

2015

1. Future Challenges: General Discussion. Faraday Discussions 177(0), 517–545 (2015) [PDF] [BibTeX]

    BibTeX: @article{d.jemmisFutureChallengesGeneral2015,
     title = {Future Challenges: General Discussion},
     shorttitle = {Future Challenges},
     author = {},
     date = {2015},
     journaltitle = {Faraday Discussions},
     volume = {177},
     number = {0},
     pages = {517--545},
     doi = {10/gf5ms3},
     url = {https://my.pcloud.com/publink/show?code=XZtIxr7Zt8MyC5erIwYzX49baog4w0S8DjUV},
     urldate = {2019-08-01}
   }
   

2. Entropy-Driven Formation of Large Icosahedral Colloidal Clusters by Spherical Confinement. Nature Materials 14(1), 56–60 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids1,2,3,4,5,6,7,8,9,10,11,12. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential1,3,6,7,8,9,10,11,12. Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure13,14. Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.

    BibTeX: @article{denijsEntropydrivenFormationLarge2015,
     title = {Entropy-Driven Formation of Large Icosahedral Colloidal Clusters by Spherical Confinement},
     author = {},
     date = {2015-01},
     journaltitle = {Nature Materials},
     volume = {14},
     number = {1},
     pages = {56--60},
     issn = {1476-4660},
     doi = {10/gf85zc},
     url = {https://www.nature.com/articles/nmat4072},
     urldate = {2019-10-01}
   }
   

3. Dynamics of Chemical Bond: General Discussion. K. Dhoke, M. Zanni, U. Harbola, R. K. Venkatraman, E. Arunan, K.-C. Lin, A. Nenov, J. Skelton, R. J. D. Miller, J. D. Hirst, V. Aquilanti, J. R. Helliwell, S. Keshavamurthy, S. Ramesh, M. Ashfold, A. Pallipurath, P. Roy Chowdhury, S. Mukhopadhyay, J. E D, H. Medhi, D. Goswami, P. Halder, W. Junge, M. Hariharan, S. K. Singh, S. Umapathy, A. Lakshmannam, M. Meedom Nielsen, S. Aravamudhan, V. Deckert, K. Ghiggino, K. Tominaga, and A. Edwards, Faraday Discussions 177, 121–154 (2015) [PDF] [BibTeX]

    BibTeX: @article{dhokeDynamicsChemicalBond2015,
     title = {Dynamics of Chemical Bond: General Discussion},
     shorttitle = {Dynamics of Chemical Bond},
     author = {Dhoke, Kunal and Zanni, Martin and Harbola, Upendra and Venkatraman, Ravi Kumar and Arunan, Elangannan and Lin, King-Chuen and Nenov, Artur and Skelton, Jonathan and Miller, R J Dwayne and Hirst, Jonathan D. and Aquilanti, Vincenzo and Helliwell, John R. and Keshavamurthy, Srihari and Ramesh, Sai and Ashfold, Mike and Pallipurath, Anuradha and Roy Chowdhury, Priyadarshi and Mukhopadhyay, Sanghamitra and E D, Jemmis and Medhi, Himani and Goswami, Debabrata and Halder, Prasenjit and Junge, Wolfgang and Hariharan, Mahesh and Singh, Santosh Kumar and Umapathy, Siva and Lakshmannam, Adithya and Meedom Nielsen, Martin and Aravamudhan, Sankarampadi and Deckert, Volker and Ghiggino, Kenneth and Tominaga, Keisuke and Edwards, Alison},
     date = {2015},
     journaltitle = {Faraday Discussions},
     shortjournal = {Faraday Discuss.},
     volume = {177},
     pages = {121--154},
     issn = {1359-6640, 1364-5498},
     doi = {10/gf5mss},
     url = {https://my.pcloud.com/publink/show?code=XZhaxr7ZFTPN6Cuqf08xjq5XSTjI4zaNU8Sy},
     urldate = {2019-08-01}
   }
   

4. Controlled Heteroaggregation of Two Types of Nanoparticles in an Aqueous Suspension. P. Dušak, A. Mertelj, S. Kralj, and D. Makovec, Journal of Colloid and Interface Science 438, 235–243 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Composite particles combining nanoparticles of different functional materials, as well as nanoclusters of nanoparticles of controlled size, can be synthesized by the assembly of nanoparticles in an aqueous suspension. Different interactions between the nanoparticles in the suspension can be applied for their heteroaggregation and controlled by engineering the surface properties of the nanoparticles. The heteroaggregation of nanoparticles in a suspension was studied on a model system composed of superparamagnetic carboxyl-functionalized silica-coated maghemite nanoparticles (cMNPs) (24nm in size) and larger, amino-functionalized, silica nanoparticles (aSNPs) (92nm). The heteroaggregates formed with electrostatic attractions between the nanoparticles displaying an opposite electrical surface charge, or with chemical interactions originating from covalent bonding between the molecules at their surfaces. The suspensions were characterized with measurements of the zeta-potential and dynamic light scattering (DLS). The heteroaggregates were analyzed by transmission (TEM) and scanning (SEM) electron microscopy. The kinetics of the heteroaggregation was followed by continuous monitoring of the changes in the average hydrodynamic size by DLS. The results show that covalent bonding is much more effective than attractive electrostatic interactions in terms of a much greater and more homogeneous coverage of the larger central aSNP by the smaller cMNPs in the outer layer.

    BibTeX: @article{dusakControlledHeteroaggregationTwo2015,
     title = {Controlled Heteroaggregation of Two Types of Nanoparticles in an Aqueous Suspension},
     author = {Dušak, Peter and Mertelj, Alenka and Kralj, Slavko and Makovec, Darko},
     date = {2015-01-15},
     journaltitle = {Journal of Colloid and Interface Science},
     shortjournal = {Journal of Colloid and Interface Science},
     volume = {438},
     pages = {235--243},
     issn = {0021-9797},
     doi = {10/f6tfsv},
     url = {http://www.sciencedirect.com/science/article/pii/S0021979714007504},
     urldate = {2019-10-01}
   }
   

5. Advanced Optical Developments for Inter-Satellite Communication. D. Goswami, 5 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: One of the most common and effective usage of free space communication (FSO) is in the information transfer between satellites, which at present is mostly based on wireless Radio frequency (RF). FSO is a telecommunications technology that transmits and receives data in the form of optical signal through an unguided channel from one point to another point. The theory of FSO is essentially the same as that for fiber optic transmission. The difference is that the energy beam is collimated and sent through clear air or space from the source to destination, rather than guided through an optical fiber. While optical fiber has emerged as the major communication channel for terrestrial communication due to the difficulty of finding effective line of sight in terrestrial space needed for FSO, it remains as one of the most effective means for space applications, especially for inter-satellite communication. Our research is focusing on such advanced optical technology as the effective transmitter for free-space communication.

    BibTeX: @article{goswamiAdvancedOpticalDevelopments2015,
     title = {Advanced {{Optical Developments}} for Inter-{{Satellite Communication}}},
     author = {Goswami, Debabrata},
     date = {2015},
     pages = {5},
     url = {http://pc.cd/LaaitalK}
   }
   

6. Lasers and Their Applications. D. Goswami, 18 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Ever since the advent of the first LASER (acronym for Light Amplification by Stimulation Emission of Radiation) in 1960, there has been a steady increase in the application of lasers. Applications have kept on becoming more and more diverse as the capability of the lasers have increased. In this chapter we will enumerate and classify many of the applications of lasers and then go on to discuss in more detail some of the more modern applications.

    BibTeX: @article{goswamiLasersTheirApplications2015,
     title = {Lasers and Their {{Applications}}},
     author = {Goswami, Debabrata},
     date = {2015},
     pages = {18},
     url = {https://my.pcloud.com/publink/show?code=XZeoxr7ZHDcE2BJfa3pk2RL7TQEYeQyTevSk}
   }
   

7. Resolution Enhancement through Microscopic Spatiotemporal Control. D. Goswami, D. Das, and S. N. Bandyopadhyay, Faraday Discussions 177(0), 203–212 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Operating at biologically benign conditions, multi-photon fluorescence imaging microscopy has benefitted immensely from recent developments in microscopic resolution enhancement. Fluorescence microscopy continues to be the best choice for experiments on live specimens, however, multi-photon fluorescence imaging often suffers from overlapping fluorescence of typical dyes used in microscopy, limiting its scope. This limitation has been the focus of our research where we show that by making simple modifications to the laser pulse structure, it is possible to resolve these overlapping fluorescence complications. Specifically, by using pairs of femtosecond pulses with variable delay in place of single pulse excitation, we show controlled fluorescence excitation or suppression of one of the fluorophores over the other through wave-packet interferometry. Such an effect prevails even after the fluorophore coherence timescale, which effectively results in a higher spatial resolution. Here we extend the effect of our pulse-pair technique to microscopic axial resolution experiments and show that such pairs of pulses can also ‘enhance’ axial resolution.

    BibTeX: @article{goswamiResolutionEnhancementMicroscopic2015,
     title = {Resolution Enhancement through Microscopic Spatiotemporal Control},
     author = {Goswami, Debabrata and Das, Dhiman and Bandyopadhyay, Soumendra Nath},
     date = {2015-04-14},
     journaltitle = {Faraday Discussions},
     shortjournal = {Faraday Discuss.},
     volume = {177},
     number = {0},
     pages = {203--212},
     issn = {1364-5498},
     doi = {10/gf5msv},
     url = {https://my.pcloud.com/publink/show?code=XZzvxr7Z0vbvki6gLSQhR76QzRco87Moa8Fy},
     urldate = {2019-08-01}
   }
   

8. Effect of Zinc Substitution on Molecular Dynamics of Protoporphyrin-IX. A. Kumar and D. Goswami, Indian Journal of Physics 89(11), 1183–1192 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: We report the effects of zinc metal substitution on the molecular dynamics of protoporphyrin-IX in dichloromethane solvent by spectrally resolving the femtosecond photon echo spectrum. We have found that the coherence and population dynamics change due to the presence of Zn metal in the protoporphyrin-IX system. Zinc metal reduces the conformational disorder in the molecular structure of protoporphyrin-IX and in turn increases the planarity of the molecule resulting in better delocalization of π-electrons in the system. This effect decreases the inhomogeneous broadening of the photon echo spectra of Zn-substituted protoporphyrin-IX.

    BibTeX: @article{kumarEffectZincSubstitution2015,
     title = {Effect of Zinc Substitution on Molecular Dynamics of Protoporphyrin-{{IX}}},
     author = {Kumar, A. and Goswami, D.},
     date = {2015-11-01},
     journaltitle = {Indian Journal of Physics},
     shortjournal = {Indian J Phys},
     volume = {89},
     number = {11},
     pages = {1183--1192},
     issn = {0974-9845},
     doi = {10/f73kth},
     url = {https://doi.org/10.1007/s12648-015-0689-5},
     urldate = {2019-08-01}
   }
   

9. Study of Two Xanthene Dyes Using Spectrally Resolved Three-Pulse Photon Echo Spectroscopy. A. Kumar, S. K. K. Kumar, S. Singhal, and D. Goswami, Current Science 108(10), 1801–1803 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Comparitive study of the molecular dynamics of two xanthene dye derivatives (Rhodamine-6G and Fluorescein-548) is reported using spectrally resolved three-pulse photon echo spectroscopy. An appreciable change in the coherence and population dynamics was observed between the two xanthene derivatives due to the presence of different functional groups. Solution of Rhodamine-6G in methanol behaves in a more coherent fashion compared to that of Fluorescein-548 dye.

    BibTeX: @article{kumarStudyTwoXanthene2015,
     title = {Study of Two Xanthene Dyes Using Spectrally Resolved Three-Pulse Photon Echo Spectroscopy},
     author = {Kumar, Ajitesh and Kumar, S. K. Karthick and Singhal, Sumit and Goswami, Debabrata},
     date = {2015},
     journaltitle = {Current Science},
     volume = {108},
     number = {10},
     eprint = {24905603},
     eprinttype = {jstor},
     pages = {1801--1803},
     issn = {0011-3891},
     url = {https://www.jstor.org/stable/24905603},
     urldate = {2019-08-01}
   }
   

10. Controlling Local Temperature in Water Using Femtosecond Optical Tweezer. D. Mondal and D. Goswami, Biomedical Optics Express 6(9), 3190–3196 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: A novel method of directly observing the effect of temperature rise in water at the vicinity of optical trap center is presented. Our approach relies on changed values of corner frequency of the optical trap that, in turn, is realized from its power spectra. Our two color experiment is a unique combination of a non-heating femtosecond trapping laser at 780 nm, coupled to a femtosecond infrared heating laser at 1560 nm, which precisely controls temperature at focal volume of the trap center using low powers (100-800 µW) at high repetition rate. The geometric ray optics model quantitatively supports our experimental data.

     BibTeX: @article{mondalControllingLocalTemperature2015,
      title = {Controlling Local Temperature in Water Using Femtosecond Optical Tweezer},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2015-09-01},
      journaltitle = {Biomedical Optics Express},
      shortjournal = {Biomed. Opt. Express, BOE},
      volume = {6},
      number = {9},
      pages = {3190--3196},
      issn = {2156-7085},
      doi = {10/gf5msh},
      url = {https://www.osapublishing.org/boe/abstract.cfm?uri=boe-6-9-3190},
      urldate = {2019-08-01}
    }
    

11. Elucidating Microscopic Structure and Dynamics in Optically Tweezed Environments. D. Roy, D. Mondal, and D. Goswami, Chemical Physics Letters 621, 203–208 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: To probe the structure and dynamics of molecules under optical trapping conditions, we exploit the effect of femtosecond Fluorescence Resonance Energy Transfer (FRET) between dye molecules coated on the surface of polystyrene microspheres of various sizes suspended in water. The use of femtosecond laser pulses enables sensitive detection through two-photon fluorescence (TPF). Unlike conventional backscatter signal, the TPF signal shows a slow counterintuitive decay for the trapped microspheres when they are not fully within the laser illuminated volume. This decay is a characteristic sign of the occurrence of the FRET process. For microspheres with sizes less than the trapping focal volume, trapping of multiple particles can occur leading to the formation of optically bound clusters. Using different laser polarizations, we also extract information about the structure and dynamics of such optically bound clusters as a consequence of FRET.

     BibTeX: @article{royElucidatingMicroscopicStructure2015,
      title = {Elucidating Microscopic Structure and Dynamics in Optically Tweezed Environments},
      author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
      date = {2015-02-04},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {621},
      pages = {203--208},
      issn = {0009-2614},
      doi = {10/f6zd8x},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261414009658},
      urldate = {2019-08-01}
    }
    

12. Exploring the Physics of Efficient Optical Trapping of Dielectric Nanoparticles with Ultrafast Pulsed Excitation. D. Roy, D. Goswami, and A. K. De, Applied Optics 54(23), 7002 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: Stable optical trapping of dielectric nanoparticles with low power high-repetition-rate ultrafast pulsed excitation has received considerable attention in recent years. However, the exact role of such excitation has been quite illusive so far since, for dielectric micron-sized particles, the trapping efficiency turns out to be similar to that of continuous-wave excitation and independent of pulse chirping. In order to provide a coherent explanation of this apparently puzzling phenomenon, we justify the superior role of high-repetition-rate pulsed excitation in dielectric nanoparticle trapping which is otherwise not possible with continuous-wave excitation at a similar average power level. We quantitatively estimate the optimal combination of pulse peak power and pulse repetition rate leading to a stable trap and discuss the role of inertial response on the dependence of trapping efficiency on pulse width. In addition, we report gradual trapping of individual quantum dots detected by a stepwise rise in a two-photon fluorescence signal from the trapped quantum dots which conclusively proves individual particle trapping.

     BibTeX: @article{royExploringPhysicsEfficient2015,
      title = {Exploring the Physics of Efficient Optical Trapping of Dielectric Nanoparticles with Ultrafast Pulsed Excitation},
      author = {Roy, Debjit and Goswami, Debabrata and De, Arijit K.},
      date = {2015-08-10},
      journaltitle = {Applied Optics},
      shortjournal = {Appl. Opt.},
      volume = {54},
      number = {23},
      pages = {7002},
      issn = {0003-6935, 1539-4522},
      doi = {10/gf5msm},
      url = {https://www.osapublishing.org/abstract.cfm?URI=ao-54-23-7002},
      urldate = {2019-08-01}
    }
    

13. Local and Global Dynamics: General Discussion. M. Zanni, E. D. Jemmis, S. Aravamudhan, E. Arunan, N. Hunt, S. Mukhopadhyay, H. J. Shepherd, S. Keshavamurthy, A. G. Dijkstra, M. Ashfold, H. P. Goswami, A. Nenov, H. Medhi, K. Ghiggino, K. Moirangthem, R. J. Dwayne Miller, D. Goswami, S. Umapathy, J. R. Helliwell, J. D. Hirst, S. Meech, S. Mukamel, B. Bagchi, and M. B.-L. Cointe, Faraday Discussions 177(0), 381–403 (2015) [PDF] [BibTeX]

     BibTeX: @article{zanniLocalGlobalDynamics2015,
      title = {Local and {{Global Dynamics}}: General Discussion},
      shorttitle = {Local and {{Global Dynamics}}},
      author = {Zanni, Martin and D.~Jemmis, E. and Aravamudhan, Sankarampadi and Arunan, Elangannan and Hunt, Neil and Mukhopadhyay, Sanghamitra and J.~Shepherd, Helena and Keshavamurthy, Srihari and G.~Dijkstra, Arend and Ashfold, Mike and Goswami, Himangshu Prabal and Nenov, Artur and Medhi, Himani and Ghiggino, Kenneth and Moirangthem, Kiran and Dwayne~Miller, R. J. and Goswami, Debabrata and Umapathy, Siva and R.~Helliwell, John and D.~Hirst, Jonathan and Meech, Stephen and Mukamel, Shaul and Bagchi, Biman and Cointe, Marylise Buron-Le},
      date = {2015},
      journaltitle = {Faraday Discussions},
      volume = {177},
      number = {0},
      pages = {381--403},
      doi = {10/gf5ms2},
      url = {https://pubs.rsc.org/en/content/articlelanding/2015/fd/c5fd90018b},
      urldate = {2019-08-01}
    }
    

14. Time and Space Resolved Methods: General Discussion. M. Zanni, J. E. D, S. Aravamudhan, A. Pallipurath, E. Arunan, C. Schnedermann, A. K. Mishra, M. Warren, J. D. Hirst, F. John, R. Pal, J. R. Helliwell, K. Moirangthem, S. Chakraborty, A. G. Dijkstra, P. R. Chowdhury, K. Ghiggino, R. J. D. Miller, S. Meech, H. Medhi, M. Hariharan, F. Ariese, A. Edwards, A. R. Mallia, S. Umapathy, M. M. Nielsen, N. Hunt, Z.-Y. Tian, J. Skelton, G. Sankar, and D. Goswami, Faraday Discussions 177(0), 263–292 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: No abstract available

     BibTeX: @article{zanniTimeSpaceResolved2015,
      title = {Time and {{Space}} Resolved {{Methods}}: General Discussion},
      shorttitle = {Time and {{Space}} Resolved {{Methods}}},
      author = {Zanni, Martin and D, Jemmis E. and Aravamudhan, Sankarampadi and Pallipurath, Anuradha and Arunan, Elangannan and Schnedermann, Christoph and Mishra, Ashok Kumar and Warren, Mark and Hirst, Jonathan D. and John, Franklin and Pal, R. and Helliwell, John R. and Moirangthem, Kiran and Chakraborty, Shamik and Dijkstra, Arend G. and Chowdhury, Priyadarshi Roy and Ghiggino, Kenneth and Miller, R. J. Dwayne and Meech, Stephen and Medhi, Himani and Hariharan, Mahesh and Ariese, Freek and Edwards, Alison and Mallia, Ajith R. and Umapathy, Siva and Nielsen, Martin Meedom and Hunt, Neil and Tian, Zhen-Yu and Skelton, Jonathan and Sankar, Gopinathan and Goswami, Debabrata},
      date = {2015-04-14},
      journaltitle = {Faraday Discussions},
      shortjournal = {Faraday Discuss.},
      volume = {177},
      number = {0},
      pages = {263--292},
      issn = {1364-5498},
      doi = {10/gf5mst},
      url = {https://pubs.rsc.org/en/content/articlelanding/2015/fd/c5fd90017d},
      urldate = {2019-08-01}
    }
    

2014

1. Effect of Isotope Substitution in Binary Liquids with Thermal-Lens Spectroscopy. I. Bhattacharyya, P. Kumar, and D. Goswami, Chemical Physics Letters 598, 35–38 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: Effect of isotope substitution from the modulation of Thermal-Lens (TL) signals in binary liquid mixtures is explored using femtosecond pump–probe mode-mismatched Z-scan TL spectroscopy. Binary solutions of water and heavy water with pure methanol at various concentrations are used for the study, where pure methanol acts as the TL marker across the different samples. The TL signal is found to be effectively modulated by isotope substitution under the experimental conditions, indicating that TL signal depends on hydrogen bonding.

    BibTeX: @article{bhattacharyyaEffectIsotopeSubstitution2014,
     title = {Effect of Isotope Substitution in Binary Liquids with {{Thermal-Lens}} Spectroscopy},
     author = {Bhattacharyya, Indrajit and Kumar, Pardeep and Goswami, Debabrata},
     date = {2014-04-08},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {598},
     pages = {35--38},
     issn = {0009-2614},
     doi = {10/f5xrr2},
     url = {http://pc.cd/PORctalK},
     urldate = {2019-08-02}
   }
   

2. Direct Observation of Coherent Oscillations in Solution Due to Microheterogeneous Environment. D. K. Das, K. Makhal, S. N. Bandyopadhyay, and D. Goswami, Scientific Reports 4, 6097 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: We report, for the first time, direct observation of coherent oscillations in the ground-state of IR775 dye due to microheterogeneous environment. Using ultrafast near-infrared degenerate pump-probe technique centered at 800 nm, we present the dynamics of IR775 in a binary mixture of methanol and chloroform at ultra-short time resolution of 30 fs. The dynamics of the dye in binary mixtures, in a time-scale of a few fs to ~740 ps, strongly varies as a function of solvent composition (volume fraction). Multi-oscillation behavior of the coherent vibration was observed, which increased with decreasing percentage of methanol in the dye mixture. Maximum number of damped oscillations were observed in 20% methanol. The observed vibrational wavepacket motion in the ground-state is periodic in nature. We needed two cosine functions to fit the coherent oscillation data as two different solvents were used. Dynamics of the dye molecule in binary mixtures can be explained by wavepacket motion in the ground potential energy surface. More is the confinement of the dye molecule in binary mixtures, more is the number of damped oscillations. The vibrational cooling time, τ2, increases with increase in the confinement of the system. The observed wavepacket oscillations in ground-state dynamics continued until 1.6 ps.

    BibTeX: @article{dasDirectObservationCoherent2014,
     title = {Direct {{Observation}} of {{Coherent Oscillations}} in {{Solution}} Due to {{Microheterogeneous Environment}}},
     author = {Das, Dipak Kumar and Makhal, Krishnandu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2014-08-18},
     journaltitle = {Scientific Reports},
     volume = {4},
     pages = {6097},
     issn = {2045-2322},
     doi = {10/gf5mth},
     url = {https://www.nature.com/articles/srep06097},
     urldate = {2019-08-01}
   }
   

3. Controlled Particle Collision Leads to Direct Observation of Docking and Fusion of Lipid Droplets in an Optical Trap. C. Ghimire, D. Koirala, M. B. Mathis, E. E. Kooijman, and H. Mao, Langmuir 30(5), 1370–1375 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: As an intracellular organelle, phospholipid-coated lipid droplets have shown increasing importance due to their expanding biological functions other than the lipid storage. The growing biological significance necessitates a close scrutiny on lipid droplets, which have been proposed to mature in a cell through processes such as fusion. Unlike phospholipid vesicles that are well-known to fuse through docking and hemifusion steps, little is known on the fusion of lipid droplets. Herein, we used laser tweezers to capture two micrometer-sized 1,2,3-trioleoylglycerol (triolein) droplets coated with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) that closely resemble intracellular lipid droplets. We started the fusion processes by a well-controlled collision between the two lipid droplets in phosphate buffer at pH 7.4. By monitoring the change in the pathway of a trapping laser that captures the collided lipid droplets, docking and physical fusion events were clearly distinguished for the first time and their lifetimes were determined with a resolution of 10 μs after postsynchronization analysis. Our method revealed that the rate-limiting docking process is affected by anions according to a Hofmeister series, which sheds light on the important role of interfacial water shedding during the process. During the physical fusion, the kinetics between bare triolein droplets is faster than lipid droplets, suggesting that breaking of phospholipid coating is involved in the process. This scenario was further supported by direct observation of a short-lived hemifusion state with ∼46 ms lifetime in POPC-coated lipid droplets, but not in bare triolein droplets.

    BibTeX: @article{ghimireControlledParticleCollision2014,
     title = {Controlled {{Particle Collision Leads}} to {{Direct Observation}} of {{Docking}} and {{Fusion}} of {{Lipid Droplets}} in an {{Optical Trap}}},
     author = {Ghimire, Chiran and Koirala, Deepak and Mathis, Malcom B. and Kooijman, Edgar E. and Mao, Hanbin},
     date = {2014-02-11},
     journaltitle = {Langmuir},
     shortjournal = {Langmuir},
     volume = {30},
     number = {5},
     pages = {1370--1375},
     issn = {0743-7463},
     doi = {10/f5swjm},
     url = {https://doi.org/10.1021/la404497v},
     urldate = {2019-10-01}
   }
   

4. Effect of Molecular Structural Isomers in Thermal Lens Spectroscopy. P. Kumar, S. Dinda, and D. Goswami, Chemical Physics Letters 601, 163–167 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: We explore the importance of molecular structure on thermal lens (TL) spectroscopy by measuring the effects of molecular isomerization on TL measurements. In particular, we present a case study for all the structural isomers of butanol, namely, normal-butanol (n-BuOH), secondary-butanol (s-BuOH), isobutanol (i-BuOH) and tertiary-butanol (t-BuOH). We argue that the molecular isomerization influences the heat convection process in two possible ways: one being a change in the molecular surface area and the other being the steric hindrance. We show that n-BuOH has the highest capability to transfer heat by convection. Branching in the molecular structure renders the system sluggish as it makes the molecular motion successively retarded due to an increase in the mean free path. This we have defined as the molecular drift that slows under thermal conditions. In our studied isomers, therefore, t-BuOH drifts the slowest.

    BibTeX: @article{kumarEffectMolecularStructural2014,
     title = {Effect of Molecular Structural Isomers in Thermal Lens Spectroscopy},
     author = {Kumar, Pardeep and Dinda, Sirshendu and Goswami, Debabrata},
     date = {2014-05},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {601},
     pages = {163--167},
     issn = {00092614},
     doi = {10/gf6bk6},
     url = {https://linkinghub.elsevier.com/retrieve/pii/S0009261414002620},
     urldate = {2019-08-12}
   }
   

5. Importance of Molecular Heat Convection in Time Resolved Thermal Lens Study of Highly Absorbing Samples. P. Kumar, A. Khan, and D. Goswami, Chemical Physics 441, 5–10 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: Our experimental study shows that in the case of strongly absorbing samples, the time resolved thermal lens (TL) signal has a distinctive new feature. Existing TL models that are only based on heat conduction cannot explain this behavior. We have therefore developed a more comprehensive model that can also explain this additional feature in the TL of strongly absorbing samples. Our model is also capable of explaining our experimental results that show how the molecular size affects the molecular heat convection.

    BibTeX: @article{kumarImportanceMolecularHeat2014,
     title = {Importance of Molecular Heat Convection in Time Resolved Thermal Lens Study of Highly Absorbing Samples},
     author = {Kumar, Pardeep and Khan, Arbaz and Goswami, Debabrata},
     date = {2014-09-30},
     journaltitle = {Chemical Physics},
     shortjournal = {Chemical Physics},
     volume = {441},
     pages = {5--10},
     issn = {0301-0104},
     doi = {10/f6kr7q},
     url = {http://www.sciencedirect.com/science/article/pii/S0301010414001724},
     urldate = {2019-08-01}
   }
   

6. Importance of Molecular Structure on the Thermophoresis of Binary Mixtures. P. Kumar and D. Goswami, The Journal of Physical Chemistry B 118(51), 14852–14859 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: Using thermal lens spectroscopy, we study the role of molecular structural isomers of butanol on the thermophoresis (or Soret effect) of binary mixtures of methanol in butanol. In this study, we show that the thermal lens signal due to the Soret effect changes its sign for all the different concentrations of binary mixtures of butanol with methanol except for the one containing tertiary-butanol. The magnitude and sign of the Soret coefficients strongly depend on the molecular structure of the isomers of butanol in the binary mixture with methanol. This isomerization dependence is in stark contrast to the expected mass dependence of the Soret effect.

    BibTeX: @article{kumarImportanceMolecularStructure2014,
     title = {Importance of {{Molecular Structure}} on the {{Thermophoresis}} of {{Binary Mixtures}}},
     author = {Kumar, Pardeep and Goswami, Debabrata},
     date = {2014-12-26},
     journaltitle = {The Journal of Physical Chemistry B},
     shortjournal = {J. Phys. Chem. B},
     volume = {118},
     number = {51},
     pages = {14852--14859},
     issn = {1520-6106},
     doi = {10/gf5ms6},
     url = {https://doi.org/10.1021/jp5079604},
     urldate = {2019-08-01}
   }
   

7. Unusual Behavior of Thermal Lens in Alcohols. P. Kumar, S. Dinda, A. Chakraborty, and D. Goswami, Physical Chemistry Chemical Physics 16(24), 12291–12298 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: We use a femtosecond pump–probe Z-scan technique to measure the thermal lens (TL) signal in a homologous series of primary alcohols. The trend in these experimentally measured TL signals deviates in a counterintuitive manner from the ones calculated using theoretical models that are only based on the macroscopic parameters. Introspection shows that the present TL theories are based on heat conduction for low absorbing samples without considering any convective mode of heat transfer. Our studies on highly absorbing samples indicate the importance of convective mode of heat transfer in TL studies.

    BibTeX: @article{kumarUnusualBehaviorThermal2014,
     title = {Unusual Behavior of Thermal Lens in Alcohols},
     author = {Kumar, Pardeep and Dinda, Sirshendu and Chakraborty, Atanu and Goswami, Debabrata},
     date = {2014},
     journaltitle = {Physical Chemistry Chemical Physics},
     volume = {16},
     number = {24},
     pages = {12291--12298},
     doi = {10/gf5npt},
     url = {https://pubs.rsc.org/en/content/articlelanding/2014/cp/c4cp00895b},
     urldate = {2019-08-02}
   }
   

8. Graphene Oxide from Silk Cocoon: A Novel Magnetic Fluorophore for Multi-Photon Imaging. M. Roy, T. S. Kusurkar, S. K. Maurya, S. K. Meena, S. K. Singh, N. Sethy, K. Bhargava, R. K. Sharma, D. Goswami, S. Sarkar, and M. Das, 3 Biotech 4(1), 67–75 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: In this work, we synthesized graphene oxide from silk cocoon embarking its new dimension as a magnetic fluorophore when compared with its present technical status, which at best is for extracting silk as a biomaterial for tissue engineering applications. We produced graphene oxide by pyrolysing the silk cocoon in an inert atmosphere. The collected raw carbon is oxidized by nitric acid that readily produces multilayer graphene oxide with nano carbon particulates. Structural properties of the graphene oxide were analyzed using scanning electron microscopy, transmission electron microscopy, Fourier transform infra-red spectroscopy, and Raman spectroscopy. The oxidized sample shows remarkable fluorescence, multi-photon imaging and magnetic properties. On increasing the excitation wavelength, the fluorescence emission intensity of the graphene oxide also increases and found maximum emission at 380 nm excitation wavelength. On studying the two photon absorption (TPA) property of aqueous graphene oxide using Z-scan technique, we found significant TPA activity at near infrared wavelength. In addition, the graphene oxide shows ferromagnetic behavior at room temperature. The observed fluorescence and magnetic property were attributed to the defects caused in the graphene oxide structure by introducing oxygen containing hydrophilic groups during the oxidation process. Previously silk cocoon has been used extensively in deriving silk-based tissue engineering materials and as gas filter. Here we show a novel application of silk cocoon by synthesizing graphene oxide based magnetic-fluorophore for bio-imaging applications.

    BibTeX: @article{royGrapheneOxideSilk2014,
     title = {Graphene Oxide from Silk Cocoon: A Novel Magnetic Fluorophore for Multi-Photon Imaging},
     shorttitle = {Graphene Oxide from Silk Cocoon},
     author = {Roy, Manas and Kusurkar, Tejas Sanjeev and Maurya, Sandeep Kumar and Meena, Sunil Kumar and Singh, Sushil Kumar and Sethy, Niroj and Bhargava, Kalpana and Sharma, Raj Kishore and Goswami, Debabrata and Sarkar, Sabyasachi and Das, Mainak},
     date = {2014-02-01},
     journaltitle = {3 Biotech},
     shortjournal = {3 Biotech},
     volume = {4},
     number = {1},
     pages = {67--75},
     issn = {2190-5738},
     doi = {10/gcb6qh},
     url = {https://doi.org/10.1007/s13205-013-0128-2},
     urldate = {2019-08-02}
   }
   

2013

1. Controlling the Femtosecond Laser-Driven Transformation of Dicyclopentadiene into Cyclopentadiene. T. Goswami, D. K. Das, and D. Goswami, Chemical Physics Letters 558, 1–7 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: Dynamics of the chemical transformation of dicyclopentadiene into cyclopentadiene in a supersonic molecular beam is elucidated using femtosecond time-resolved degenerate pump–probe mass spectrometry. Control of this ultrafast chemical reaction is achieved by using linearly chirped frequency modulated pulses. We show that negatively chirped femtosecond laser pulses enhance the cyclopentadiene photoproduct yield by an order of magnitude as compared to that of the unmodulated or the positively chirped pulses. This demonstrates that the phase structure of femtosecond laser pulse plays an important role in determining the outcome of a chemical reaction.

    BibTeX: @article{goswamiControllingFemtosecondLaserdriven2013,
     title = {Controlling the Femtosecond Laser-Driven Transformation of Dicyclopentadiene into Cyclopentadiene},
     author = {Goswami, Tapas and Das, Dipak K. and Goswami, Debabrata},
     date = {2013-02-12},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {558},
     pages = {1--7},
     issn = {0009-2614},
     doi = {10/f4nnb2},
     url = {https://my.pcloud.com/publink/show?code=XZFvxr7ZpduyXffXsJj4NXDLmSt1zLjBhELV},
     urldate = {2019-08-02}
   }
   

2. Spectrally Resolved Photon-Echo Spectroscopy of Rhodamine-6G. A. Kumar, S. K. Karthick, and D. Goswami, Journal of spectroscopy and dynamics 3(1), 2 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: Wavelength dependent study of a laser dye: Rhodamine-6G (Rh6G) by using spectrally resolved photon-echo spectroscopy is presented. The coherence and population dynamics of Rh6G solution in methanol changes as the excitation wavelength is tuned near its absorption maxima of 528 nm. Specifically, the central wavelength of the femtosecond laser pulse was set to 535 nm and to 560 nm while the respective spectra of the photon-echo signals were collected. This gives information on how the ultrafast dynamics of the Rh6G molecule changes with a change in the excitation wavelength.

    BibTeX: @article{kumarSpectrallyResolvedPhotonecho2013,
     title = {Spectrally Resolved Photon-Echo Spectroscopy of {{Rhodamine-6G}}},
     author = {Kumar, Ajitesh and Karthick, S. K. and Goswami, D.},
     date = {2013-02},
     journaltitle = {Journal of spectroscopy and dynamics},
     shortjournal = {J Spectrosc Dyn},
     volume = {3},
     number = {1},
     eprint = {24098869},
     eprinttype = {pmid},
     pages = {2},
     issn = {2249-2704},
     url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790070/},
     urldate = {2019-08-02},
     pmcid = {PMC3790070}
   }
   

3. Real-Space Studies of the Structure and Dynamics of Self-Assembled Colloidal Clusters. R. W. Perry, G. Meng, T. G. Dimiduk, J. Fung, and V. N. Manoharan, Faraday Discussions 159(0), 211–234 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: The energetics and assembly pathways of small clusters may yield insights into processes occurring at the earliest stages of nucleation. We use a model system consisting of micrometer-sized, spherical colloidal particles to study the structure and dynamics of small clusters, where the number of particles is small (N ≤ 10). The particles interact through a short-range depletion attraction with a depth of a few kBT. We describe two methods to form colloidal clusters, one based on isolating the particles in microwells and another based on directly assembling clusters in the gas phase using optical tweezers. We use the first technique to obtain ensemble-averaged probabilities of cluster structures as a function of N. These experiments show that clusters with symmetries compatible with crystalline order are rarely formed under equilibrium conditions. We use the second technique to study the dynamics of the clusters, and in particular how they transition between free-energy minima. To monitor the clusters we use a fast three-dimensional imaging technique, digital holographic microscopy, that can resolve the positions of each particle in the cluster with 30–45 nm precision on millisecond timescales. The real-space measurements allow us to obtain estimates for the lifetimes of the energy minima and the transition states. It is not yet clear whether the observed dynamics are relevant for small nuclei, which may not have sufficient time to transition between states before other particles or clusters attach to them. However, the measurements do provide some glimpses into how systems containing a small number of particles traverse their free-energy landscape.

    BibTeX: @article{perryRealspaceStudiesStructure2013,
     title = {Real-Space Studies of the Structure and Dynamics of Self-Assembled Colloidal Clusters},
     author = {Perry, Rebecca W. and Meng, Guangnan and Dimiduk, Thomas G. and Fung, Jerome and Manoharan, Vinothan N.},
     date = {2013-03-18},
     journaltitle = {Faraday Discussions},
     shortjournal = {Faraday Discuss.},
     volume = {159},
     number = {0},
     pages = {211--234},
     issn = {1364-5498},
     doi = {10/gfv7xg},
     url = {https://pubs.rsc.org/en/content/articlelanding/2012/fd/c2fd20061a},
     urldate = {2019-10-01}
   }
   

4. Polarization Induced Control of Multiple Fluorescence from a Molecule. Chemical Physics Letters 579, 45–50 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: We show novel dual fluorescent behavior of a popular indocyanine dye molecule, IR125, in dimethyl-sulfoxide solvent when excited at 527nm instead of t…

    BibTeX: @article{PolarizationInducedControl2013,
     title = {Polarization Induced Control of Multiple Fluorescence from a Molecule},
     date = {2013-07-30},
     journaltitle = {Chemical Physics Letters},
     volume = {579},
     pages = {45--50},
     issn = {0009-2614},
     doi = {10/f453dq},
     url = {https://www.sciencedirect.com/science/article/pii/S0009261413008026},
     urldate = {2019-08-02}
   }
   

2012

1. Chirp and Polarization Control of Femtosecond Molecular Fragmentation. T. Goswami, D. K. Das, S. K. Karthick Kumar, and D. Goswami, Indian Journal of Physics 86(3), 181–185 (2012) [Abstract] [PDF] [BibTeX]

   Abstract: We explore the simultaneous effect of chirp and polarization as the two control parameters for non-resonant photo-dissociation of n-propyl benzene. Experiments performed over a wide range of laser intensities show that these two control knobs behave mutually exclusively. Specifically, for the coherently enhanced fragments (C3H3 +, C5H5 +) with negatively chirped pulses and C6H5 + with positively chirped pulses, polarization effect is the same as compared to that in the case of transform-limited pulses. Though a change in polarization affects the overall fragmentation efficiency, the fragmentation pattern of n-propyl benzene molecule remains unaffected in contrast to the chirp case.

    BibTeX: @article{goswamiChirpPolarizationControl2012,
     title = {Chirp and Polarization Control of Femtosecond Molecular Fragmentation},
     author = {Goswami, T. and Das, D. K. and Karthick Kumar, S. K. and Goswami, D.},
     date = {2012-03-01},
     journaltitle = {Indian Journal of Physics},
     shortjournal = {Indian J Phys},
     volume = {86},
     number = {3},
     pages = {181--185},
     issn = {0974-9845},
     doi = {10/f3xs5c},
     url = {https://my.pcloud.com/publink/show?code=XZXvxr7ZAeDqROTwM5f4IAxCCHc87VQw2hJ7},
     urldate = {2019-08-02}
   }
   

2. Exploring Control Parameters of Two Photon Processes in Solutions. D. Goswami and A. Nag, Journal of Chemical Sciences 124(1), 281–289 (2012) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon microscopy depends extensively on the two-photon absorption cross sections of biologically relevant chromophores. High repetition rate (HRR) lasers are essential in multiphoton microscopy for generating satisfactory signal to noise at low average powers. However, HRR lasers generate thermal distortions in samples even with the slightest single photon absorption. We use an optical chopper with HRR lasers to intermittently ‘blank’ irradiation and effectively minimize thermal effects to result in a femtosecond z-scan setup that precisely measures the two-photon absorption (TPA) cross-sections of chromophores. Though several experimental factors impact such TPA measurements, a systematic effort to modulate and influence TPA characteristics is yet to evolve. Here, we present the effect of several control parameters on the TPA process that are independent of chromophore characteristics for femtosecond laser pulse based measurements; and demonstrate how the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization can become effective control parameters for such nonlinear optical properties. Open image in new window Graphical Abstract We demonstrate how, irrespective of chromophore characteristics, the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization are effective control parameters for nonlinear optical properties arising from two-photon processes.

    BibTeX: @article{goswamiExploringControlParameters2012,
     title = {Exploring Control Parameters of Two Photon Processes in Solutions},
     author = {Goswami, Debabrata and Nag, Amit},
     date = {2012-01-01},
     journaltitle = {Journal of Chemical Sciences},
     shortjournal = {J Chem Sci},
     volume = {124},
     number = {1},
     pages = {281--289},
     issn = {0973-7103},
     doi = {10/f3wxbj},
     url = {https://doi.org/10.1007/s12039-012-0227-3},
     urldate = {2019-08-02}
   }
   

3. Ultrafast Nonlinear Optical Response of Carbon Nanotubes Functionalized with Water Soluble Porphyrin. J. Gupta, C. Vijayan, S. K. Maurya, and D. Goswami, Optics Communications 285(7), 1920–1924 (2012) [Abstract] [PDF] [BibTeX]

   Abstract: A new nanocomposite is obtained by functionalizing carbon nanotubes (CNTs) with a water soluble metalloprophyrin using a simple chemical technique and characterized by optical absorption, IR, and Raman spectroscopy. Results from spectroscopic studies indicate the noncovalent nature of interaction between CNTs and porphyrin. The ultrafast nonlinear response is characterized by measuring the nonlinear absorption coefficient and refractive index by z-scan technique in the femtosecond pulse regime. The nanocomposite is found to exhibit two-photon absorption (TPA) with a reasonably large nonlinear optical coefficient, whereas pure CNTs is known to exhibit saturable absorption. Design of such water soluble nanocomposites offers scope for obtaining materials with enhanced ultrafast optical nonlinearity.

    BibTeX: @article{guptaUltrafastNonlinearOptical2012,
     title = {Ultrafast Nonlinear Optical Response of Carbon Nanotubes Functionalized with Water Soluble Porphyrin},
     author = {Gupta, Jyotsana and Vijayan, C. and Maurya, Sandeep Kumar and Goswami, D.},
     date = {2012-04-01},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {285},
     number = {7},
     pages = {1920--1924},
     issn = {0030-4018},
     doi = {10/fzw9zm},
     url = {http://www.sciencedirect.com/science/article/pii/S0030401811014532},
     urldate = {2019-08-02}
   }
   

4. Effect of Linear Chirp on Femtosecond Two-Photon Processes in Solution. A. Nag and D. Goswami, Journal of spectroscopy and dynamics 2(3), (2012) [Abstract] [PDF] [BibTeX]

   Abstract: Coherent control via linear chirping a femtosecond laser pulse holds the promise of a potent spectroscopic tool in the study of two-photon processes in condensed phase. Here, we show modulation in the two-photon absorption and fluorescence of several common dyes in solution by simple phase ordering of femtosecond laser pulse into a linearly frequency chirped pulse. However, the modulation is dependent on associated solvent properties as the coherence is lost rapidly in the solution phase. Also, systematic effects are mostly seen only over a limited range of chirp since it is an interplay of two opposing effects on two-photon processes—linear chirp enhancing it while the associated pulse broadening reducing it.

    BibTeX: @article{nagEffectLinearChirp2012,
     title = {Effect of Linear Chirp on Femtosecond Two-Photon Processes in Solution},
     author = {Nag, Amit and Goswami, Debabrata},
     date = {2012-08-31},
     journaltitle = {Journal of spectroscopy and dynamics},
     shortjournal = {J Spectrosc Dyn},
     volume = {2},
     number = {3},
     eprint = {24364002},
     eprinttype = {pmid},
     issn = {2249-2704},
     url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3868930/},
     urldate = {2019-08-02},
     pmcid = {PMC3868930}
   }
   

2011

1. Probing Intermolecular Interaction through Thermal-Lens Spectroscopy. I. Bhattacharyya, P. Kumar, and D. Goswami, The Journal of Physical Chemistry B 115(2), 262–268 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Binary liquid mixtures are studied using femtosecond pump−probe thermal-lens (TL) spectroscopy. Changes in the measured TL signals as a function of relative concentration of binary mixtures show that these result from a combined effect of physical and molecular properties of the constituent binary liquids. The experimental TL values deviate from the ones calculated from phenomenological equations. These, we argue, are due to an underestimation of the influence of molecular interactions when the TL signals are calculated by using physical parameters only.

    BibTeX: @article{bhattacharyyaProbingIntermolecularInteraction2011,
     title = {Probing {{Intermolecular Interaction}} through {{Thermal-Lens Spectroscopy}}},
     author = {Bhattacharyya, Indrajit and Kumar, Pardeep and Goswami, Debabrata},
     date = {2011-01-20},
     journaltitle = {The Journal of Physical Chemistry B},
     shortjournal = {J. Phys. Chem. B},
     volume = {115},
     number = {2},
     pages = {262--268},
     issn = {1520-6106},
     doi = {10/d9mz5f},
     url = {https://doi.org/10.1021/jp1062429},
     urldate = {2019-08-14}
   }
   

2. Two-Photon-Absorption Technique for Selective Detection of Copper(II) Ions in Aqueous Solution Using a Dansyl–Pyrene Conjugate. V. Chandrasekhar, M. D. Pandey, S. K. Maurya, P. Sen, and D. Goswami, Chemistry – An Asian Journal 6(9), 2246–2250 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Rhythm is a dansyl: A novel dansyl–pyrene conjugate functions as a fluorescence signaling unit showing strong fluorescence quenching upon interaction with copper(II) metal ions. On the other hand, the two-photon absorption (TPA) cross-section increased from 374 to 3022 GM (at 770 nm) upon interaction with copper(II) ions, thus allowing their selective detection in aqueous solutions.

    BibTeX: @article{chandrasekharTwoPhotonAbsorptionTechniqueSelective2011,
     title = {Two-{{Photon-Absorption Technique}} for {{Selective Detection}} of {{Copper}}({{II}}) {{Ions}} in {{Aqueous Solution Using}} a {{Dansyl}}–{{Pyrene Conjugate}}},
     author = {Chandrasekhar, Vadapalli and Pandey, Mrituanjay D. and Maurya, Sandeep Kumar and Sen, Pratik and Goswami, Debabrata},
     date = {2011},
     journaltitle = {Chemistry – An Asian Journal},
     volume = {6},
     number = {9},
     pages = {2246--2250},
     issn = {1861-471X},
     doi = {10/c5ft2w},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/asia.201100032},
     urldate = {2019-08-02}
   }
   

3. Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping: A Spatiotemporal Approach. A. K. De and D. Goswami, International Reviews in Physical Chemistry 30(3), 275–299 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: This account reviews some recent studies pursued in our group on several control experiments with important applications in (one-photon) confocal and two-photon fluorescence laser-scanning microscopy and optical trapping with laser tweezers. We explore the simultaneous control of internal and external (i.e. centre-of-mass motion) degrees of freedom, which require the coupling of various control parameters to result in the spatiotemporal control. Of particular interest to us is the implementation of such control schemes in living systems. A live cell is a system of a large number of different molecules which combine and interact to generate complex structures and functions. These combinations and interactions of molecules need to be choreographed perfectly in time and space to achieve intended intra-cellular functions. Spatiotemporal control promises to be a versatile tool for dynamical control of spatially manipulated bio-molecules.

    BibTeX: @article{deControllingMolecularMotions2011,
     title = {Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping: A Spatiotemporal Approach},
     shorttitle = {Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2011-07-01},
     journaltitle = {International Reviews in Physical Chemistry},
     volume = {30},
     number = {3},
     pages = {275--299},
     issn = {0144-235X},
     doi = {10/fmhbzc},
     url = {https://doi.org/10.1080/0144235X.2011.603237},
     urldate = {2019-08-13}
   }
   

4. Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy. A. K. De, D. Roy, and D. Goswami, Physical Review A 83(1), 015402 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: We show fluorescence-detected quantum interference in a microscope setup and demonstrate selective enhancement or suppression of fluorophores using femtosecond pulse-pair excitation with periodic modulation of the interpulse phase.

    BibTeX: @article{deFluorophoreDiscriminationTracing2011,
     title = {Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2011-01-21},
     journaltitle = {Physical Review A},
     shortjournal = {Phys. Rev. A},
     volume = {83},
     number = {1},
     pages = {015402},
     doi = {10/c73nhs},
     url = {https://link.aps.org/doi/10.1103/PhysRevA.83.015402},
     urldate = {2019-08-14}
   }
   

5. Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission. A. K. De, D. Roy, and D. Goswami, Journal of Biomedical Optics 16(10), 100505 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Controlling two-photon molecular fluorescence leading to selective fluorophore excitation has been a long sought after goal in fluorescence microscopy. In this letter, we thoroughly explore selective fluorescence suppression through simultaneous two-photon absorption by two different fluorophores followed by selective one-photon stimulated emission for one particular fluorophore. We achieve this by precisely controlling the time delay between two identical ultrafast near infrared laser pulses.

    BibTeX: @article{deSelectiveTwophotonFluorescence2011,
     title = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission},
     shorttitle = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation},
     author = {De, Arijit K. and Roy, Debjit and Goswami, Debabrata},
     date = {2011-10},
     journaltitle = {Journal of Biomedical Optics},
     shortjournal = {JBO},
     volume = {16},
     number = {10},
     pages = {100505},
     issn = {1083-3668, 1560-2281},
     doi = {10/fqkzpp},
     url = {https://my.pcloud.com/publink/show?code=XZoNxr7Zgv99AAhjLt4lAwzfutsBwYsdJNvy},
     urldate = {2019-08-02}
   }
   

6. Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers. A. K. De, D. Roy, and D. Goswami, CURRENT SCIENCE 101(7), 4 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: We show how two-photon fluorescence signal can be used as an effective detection scheme for trapping particles of any size in comparison to methods using back-scattered light. Development of such a diagnostic scheme allows us a direct observation of trapping a single nanoparticle, which shows new directions to spectroscopy at the single-molecule level in solution.

    BibTeX: @article{deTwophotonFluorescenceDiagnostics2011,
     title = {Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2011},
     journaltitle = {CURRENT SCIENCE},
     volume = {101},
     number = {7},
     pages = {4},
     url = {https://my.pcloud.com/publink/show?code=XZyaxr7ZQuCnGQH0PFBeRMoMq6mRURASwEJk}
   }
   

7. Towards Using Molecular States as Qubits. D. Goswami, T. Goswami, S. K. K. Kumar, and D. K. Das, AIP Conference Proceedings 1384(1), 251–253 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Molecular systems are presented as possible qubit systems by exploring non‐resonant molecular fragmentation of n‐propyl benzene with femtosecond laser pulses as a model case. We show that such laser fragmentation process is dependent on the phase and polarization characteristics of the laser. The effect of the chirp and polarization of the femtosecond pulse when applied simultaneously is mutually independent of each other, which makes chirp and polarization as useful ‘logic’ implementing parameters for such molecular qubits.

    BibTeX: @article{goswamiUsingMolecularStates2011,
     title = {Towards {{Using Molecular States}} as {{Qubits}}},
     author = {Goswami, Debabrata and Goswami, Tapas and Kumar, S. K. Karthick and Das, Dipak K.},
     date = {2011-09-23},
     journaltitle = {AIP Conference Proceedings},
     shortjournal = {AIP Conference Proceedings},
     volume = {1384},
     number = {1},
     pages = {251--253},
     issn = {0094-243X},
     doi = {10/bfnp4m},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.3635869},
     urldate = {2019-08-02}
   }
   

8. An Efficient Nanocomposite Based on Carbon Nanotubes Functionalized with a Fluorescent Ink for Ultrafast Optical Limiting. J. Gupta, C. Vijayan, S. K. Maurya, and D. Goswami, Materials Letters 65(5), 915–917 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Functionalization of CNTs with different kinds of molecules is known to alter the optical properties of CNTs, leading to the development of new nanocomposites of interest to optoelctronics. This paper presents the design of a new and efficient optical limiting material based on carbon nanotubes (CNTs) functionalized with a commercial fluorescent ink. High resolution transmission electron microscopy (HRTEM) and optical spectroscopy indicate that the ink molecules get noncovalently attached to the surface of the CNTs. The mechanism of optical nonlinearity of the CNTs gets modified after functionalization. Z-scan studies on functionalized CNTs performed using mode-locked Ti:Sapphire femtosecond pulses at 780nm reveal the predominance of two photon absorption (TPA). Efficient and low threshold ultrafast optical limiting is demonstrated in the new nanocomposite.

    BibTeX: @article{guptaEfficientNanocompositeBased2011,
     title = {An Efficient Nanocomposite Based on Carbon Nanotubes Functionalized with a Fluorescent Ink for Ultrafast Optical Limiting},
     author = {Gupta, Jyotsana and Vijayan, C. and Maurya, Sandeep Kumar and Goswami, D.},
     date = {2011-03-15},
     journaltitle = {Materials Letters},
     shortjournal = {Materials Letters},
     volume = {65},
     number = {5},
     pages = {915--917},
     issn = {0167-577X},
     doi = {10/cd5dqh},
     url = {http://www.sciencedirect.com/science/article/pii/S0167577X10010554},
     urldate = {2019-08-13}
   }
   

9. Efficient Ultrafast Optical Limiting Using Single Walled Carbon Nanotubes Functionalized Noncovalently with Free Base and Metalloporphyrins. J. Gupta, C. Vijayan, S. K. Maurya, and D. Goswami, Journal of Applied Physics 109(11), 113101 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: The present work is on the linear and third order nonlinear optical properties of single walled carbon nanotubes functionalized noncovalently with free base porphyrin and a metalloporphyrin separately. The functionalized carbon nanotubes (CNTs) are soluble in dimethylformamide, and the microscopic images show that the porphyrin molecules are attached to the surface of the CNTs. The interaction between CNTs and porphyrins is noncovalent and probably due to π-π interaction as both CNTs and porphyrins have π-electron rich structures. The samples exhibit large ultrafast nonlinear absorption as evident from the open aperture z-scan studies performed using mode-locked Ti:Sapphire femtosecond pulses at 780 nm. The mechanisms of optical nonlinearity of the functionalized CNTs appear to be two photon absorption along with nonlinear scattering with a small contribution from saturable absorption, whereas nonfunctionalized CNTs are known to exhibit saturable absorption. The value of the nonlinear absorption coefficient for the CNTs functionalized with the free base porphyrin is one order smaller than that for CNTs functionalized with metalloporphyrin. Efficient low threshold ultrafast optical limiting is demonstrated for both types of functionalized CNTs.

    BibTeX: @article{guptaEfficientUltrafastOptical2011,
     title = {Efficient Ultrafast Optical Limiting Using Single Walled Carbon Nanotubes Functionalized Noncovalently with Free Base and Metalloporphyrins},
     author = {Gupta, Jyotsana and Vijayan, C. and Maurya, Sandeep Kumar and Goswami, D.},
     date = {2011-06},
     journaltitle = {Journal of Applied Physics},
     shortjournal = {Journal of Applied Physics},
     volume = {109},
     number = {11},
     pages = {113101},
     issn = {0021-8979, 1089-7550},
     doi = {10/cx5v4x},
     url = {http://aip.scitation.org/doi/10.1063/1.3587178},
     urldate = {2019-08-13}
   }
   

10. Structure and Hydrogen Bond Vibrations of the Jet-Cooled 1:1 Complex between 7-Azaindole and Formamide: A Laser-Induced Fluorescence Spectroscopy Study. M. K. Hazra, M. Mukherjee, D. Goswami, and T. Chakraborty, Chemical Physics Letters 503(4), 203–209 (2011) [Abstract] [PDF] [BibTeX]

    Abstract: Laser-induced fluorescence spectra of 7-azaindole⋯formamide complex are measured in a supersonic free jet expansion. Calculation at MP2/6-311++G∗∗ level predicts a cyclic doubly hydrogen-bonded structure for the complex is favoured most in the ground state. The complex emits only UV fluorescence from the locally excited state and tautomerization is inhibited under the jet-cooled environment. This photophysical behavior is consistent with the predictions of CIS/6-311++G∗∗ and TDDFT/6-311++G∗∗ calculations. The low-frequency bands in the fluorescence spectra are assigned to different hydrogen bond modes of the complex, and the spectra reveal signatures of mixing between inter- and intra-molecular vibrational modes in the excited state.

     BibTeX: @article{hazraStructureHydrogenBond2011,
      title = {Structure and Hydrogen Bond Vibrations of the Jet-Cooled 1:1 Complex between 7-Azaindole and Formamide: {{A}} Laser-Induced Fluorescence Spectroscopy Study},
      shorttitle = {Structure and Hydrogen Bond Vibrations of the Jet-Cooled 1},
      author = {Hazra, Montu K. and Mukherjee, Moitrayee and Goswami, Debabrata and Chakraborty, Tapas},
      date = {2011-02-17},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {503},
      number = {4},
      pages = {203--209},
      issn = {0009-2614},
      doi = {10/bj9kdz},
      url = {http://www.sciencedirect.com/science/article/pii/S000926141100025X},
      urldate = {2019-08-13}
    }
    

11. Microscopic Probing of Two-Photon Fluorescence for Cancer Diagnosis. A. Kumar De, N. N. Mutyal, and D. Goswami, Current science 100(3), 294–295 (2011) [Abstract] [PDF] [BibTeX]

    Abstract: For decades, molecular fluorescence-based microscopic methods have been a standard tool for wide-ranging biological applications1. Many molecules within the live cell (e.g. amino acids like tryptophan and tyrosine, riboflavins, nicotinamides, etc.) are fluorescent by themselves, and therefore are potential candidates to be probed using fluorescence microscopy. This phenomenon of intrinsic fluorescence is known as ‘auto-fluorescence’. Amongst various fluorescence-based imaging techniques, multi-photon fluorescence microscopy2,3 has been shown to be an excellent candidate for quantitative auto-fluorescence detection. Recently, it has been demonstrated that multi-photon excited auto-fluorescence can be a significant marker for cancer4,5. Here we describe the salient features of a multiphoton fluorescence microscope constructed in our laboratory and report its potential applications in cancer diagnosis.

     BibTeX: @article{kumardeMicroscopicProbingTwophoton2011,
      title = {Microscopic Probing of Two-Photon Fluorescence for Cancer Diagnosis},
      author = {Kumar De, Arijit and Mutyal, Nikhil N. and Goswami, Debabrata},
      date = {2011-02-10},
      journaltitle = {Current science},
      shortjournal = {Curr Sci},
      volume = {100},
      number = {3},
      eprint = {23814312},
      eprinttype = {pmid},
      pages = {294--295},
      issn = {0011-3891},
      url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3695547/},
      urldate = {2019-08-14},
      pmcid = {PMC3695547}
    }
    

2010

1. Decoding Coherent Information in Femtosecond Shaped Laser Pulses. I. Bhattacharyya, A. Dutta, S. Ashtekar, S. K. Maurya, and D. Goswami, CURRENT SCIENCE 99(4), 10 (2010) [Abstract] [BibTeX]

   Abstract: We report here an experimental demonstration of a pulse decoding technique from spectral analysis of femtosecond pulses. This technique is based on a single-step Fourier domain inversion algorithm and shows the impact of the spectral window function on the retrieval of the signal pulse. Using two femtosecond laser pulses at 780 and 1560 nm from a fibre laser, we have shown that even when the spectral content of the reference pulse is far from a narrow band limit (as much as a quarter of its entire spectral content for our conditions), the single-step retrieval analysis using spectral windowing in the Fourier domain works efficiently. The enhanced signal levels possible due to the wider spectral window are critical in the unambiguous description of laser pulses, which would have potential application in the retrieval of comparatively weak and complex ultra-short pulses as is often needed in pulse shaping applications and coherent optical communications.

    BibTeX: @article{bhattacharyyaDecodingCoherentInformation2010,
     title = {Decoding Coherent Information in Femtosecond Shaped Laser Pulses},
     author = {Bhattacharyya, Indrajit and Dutta, Aveek and Ashtekar, Sumit and Maurya, Sandeep Kumar and Goswami, Debabrata},
     date = {2010},
     journaltitle = {CURRENT SCIENCE},
     volume = {99},
     number = {4},
     pages = {10}
   }
   

2. Synthesis, Structure, and Two-Photon Absorption Studies of a Phosphorus-Based Tris Hydrazone Ligand (S)P[N(Me)N═CH-C6H3-2-OH-4-N(CH2CH3)2]3 and Its Metal Complexes. V. Chandrasekhar, R. Azhakar, B. Murugesapandian, T. Senapati, P. Bag, M. D. Pandey, S. K. Maurya, and D. Goswami, Inorganic Chemistry 49(9), 4008–4016 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: A phosphorus-supported multidentate ligand (S)P[N(Me)N═CH-C6H3-2-OH-4-N(CH 2CH3)2]3 (1) has been used to prepare mononuclear complexes LM [M = Fe (2) Co (3)] and trinuclear complexes L2M3 [M = Mn (4), Ni (5), Zn (6), Mg (7), Cd (8)]. In both 2 and 3 the ligand binds the metal ion in a facial coordination mode utilizing three imino nitrogen (3N) and three phenolic oxygen (3O) atoms. The molecular structures of L2Mn3, L2Ni3, L2Zn3, L2Mg3, and L2Cd3 (4−8) are similar; two trihydrazone ligands are involved in coordination to hold the three metal ions in a linear fashion. Each of the trishydrazone ligands behaves as a trianionic hexadentate ligand providing three imino and three phenolic oxygen atoms for coordination to the metal ions. The coordination environment around the two terminal metal ions is similar (3N, 3O) while the central metal ion has a 6O coordination environment. Third-order non-linear optical properties of these compounds as measured by their two-photon absorption (TPA) cross section reveals that while 1 does not possess obvious TPA activity, complexes 2 (3213 GM) and 4 (3516 GM) possess a large TPA cross section at 770 nm.

    BibTeX: @article{chandrasekharSynthesisStructureTwoPhoton2010,
     title = {Synthesis, {{Structure}}, and {{Two-Photon Absorption Studies}} of a {{Phosphorus-Based Tris Hydrazone Ligand}} ({{S}}){{P}}[{{N}}({{Me}}){{N}}═{{CH-C6H3-2-OH-4-N}}({{CH2CH3}})2]3 and {{Its Metal Complexes}}},
     author = {Chandrasekhar, Vadapalli and Azhakar, Ramachandran and Murugesapandian, Balasubramanian and Senapati, Tapas and Bag, Prasenjit and Pandey, Mrituanjay D. and Maurya, Sandeep Kumar and Goswami, Debabrata},
     date = {2010-05-03},
     journaltitle = {Inorganic Chemistry},
     shortjournal = {Inorg. Chem.},
     volume = {49},
     number = {9},
     pages = {4008--4016},
     issn = {0020-1669},
     doi = {10/bvqgfp},
     url = {https://doi.org/10.1021/ic901531e},
     urldate = {2019-08-14}
   }
   

3. Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation. A. K. De, D. Roy, and D. Goswami, Journal of Biomedical Optics 15(6), 060502 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: Selective excitation of a particular fluorophore in the presence of others demands clever design of the optical field interacting with the molecules. We describe the use of 20- to 50-GHz pulse-train excitation leading to two-photon absorption, followed by successive one-photon stimulated emission as a potential technique in the context of controlling two-photon molecular fluorescence, with applications in microscopy.

    BibTeX: @article{deSelectiveSuppressionTwophoton2010,
     title = {Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2010-11},
     journaltitle = {Journal of Biomedical Optics},
     shortjournal = {JBO},
     volume = {15},
     number = {6},
     pages = {060502},
     issn = {1083-3668, 1560-2281},
     doi = {10/cp9rx2},
     url = {https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-15/issue-6/060502/Selective-suppression-of-two-photon-fluorescence-in-laser-scanning-microscopy/10.1117/1.3509383.short},
     urldate = {2019-08-14}
   }
   

4. Optical Trapping with High Forces Reveals Unexpected Behaviors of Prion Fibrils. J. Dong, C. E. Castro, M. C. Boyce, M. J. Lang, and S. Lindquist, Nature Structural & Molecular Biology 17(12), 1422–1430 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: Amyloid fibrils feature in many human diseases and in epigenetic memory, but understanding their molecular structure has been difficult. Now, through a combination of optical trapping and fluorescent imaging to examine amyloid fibrils of the yeast prion protein Sup35, the unexpected unfolding of individual subdomains has been detected, suggesting strong noncovalent interactions maintain the fibril even if individual monomers unfold.

    BibTeX: @article{dongOpticalTrappingHigh2010,
     title = {Optical Trapping with High Forces Reveals Unexpected Behaviors of Prion Fibrils},
     author = {Dong, Jijun and Castro, Carlos E. and Boyce, Mary C. and Lang, Matthew J. and Lindquist, Susan},
     date = {2010-12},
     journaltitle = {Nature Structural \& Molecular Biology},
     shortjournal = {Nat Struct Mol Biol},
     volume = {17},
     number = {12},
     pages = {1422--1430},
     issn = {1545-9985},
     doi = {10/cwz3hf},
     url = {https://www.nature.com/articles/nsmb.1954},
     urldate = {2019-10-01}
   }
   

5. Aggregation-Disaggregation Transition of DNA-coated Colloids: Experiments and Theory. R. Dreyfus, Physical Review E 81(4), (2010) [BibTeX]

    BibTeX: @article{dreyfusAggregationdisaggregationTransitionDNAcoated2010,
     title = {Aggregation-Disaggregation Transition of {{DNA-coated}} Colloids: {{Experiments}} and Theory},
     shorttitle = {Aggregation-Disaggregation Transition of {{DNA-coated}} Colloids},
     author = {Dreyfus, Rémi},
     date = {2010},
     journaltitle = {Physical Review E},
     shortjournal = {Phys. Rev. E},
     volume = {81},
     number = {4},
     doi = {10/dv9dh3}
   }
   

6. Self-Assembled Plasmonic Nanoparticle Clusters. J. A. Fan, C. Wu, K. Bao, J. Bao, R. Bardhan, N. J. Halas, V. N. Manoharan, P. Nordlander, G. Shvets, and F. Capasso, Science 328(5982), 1135–1138 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials. A hierarchy of nanoscale optical structures is created from nanoparticles that have metal shells and dielectric cores. A hierarchy of nanoscale optical structures is created from nanoparticles that have metal shells and dielectric cores.

    BibTeX: @article{fanSelfAssembledPlasmonicNanoparticle2010,
     title = {Self-{{Assembled Plasmonic Nanoparticle Clusters}}},
     author = {Fan, Jonathan A. and Wu, Chihhui and Bao, Kui and Bao, Jiming and Bardhan, Rizia and Halas, Naomi J. and Manoharan, Vinothan N. and Nordlander, Peter and Shvets, Gennady and Capasso, Federico},
     date = {2010-05-28},
     journaltitle = {Science},
     volume = {328},
     number = {5982},
     eprint = {20508125},
     eprinttype = {pmid},
     pages = {1135--1138},
     issn = {0036-8075, 1095-9203},
     doi = {10/cdpt9m},
     url = {https://science.sciencemag.org/content/328/5982/1135},
     urldate = {2019-10-01}
   }
   

7. Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy. D. Goswami and A. Kumar De, Biophysical Journal 98(3), 586a (2010) [Abstract] [PDF] [BibTeX]

   Abstract: Confocal microscopy, one of the modern day fluorescence laser-scanning microscopic techniques, is suffered from having sufficient out-of-focus signal. On the other hand, in multiphoton microscopy ultrafast laser pulses are commonly used to circumvent low multiphoton absorption cross-sections of common fluorophores; due to broad overlapping two-photon absorption (TPA) spectra of fluorophores and large spectral bandwidth of a short pulse, simultaneous excitation of many fluorophores is common demanding selective excitation of individual fluorophores if required. Addressing the first issue, our recent work has shown that ultrafast one-photon pulsed illumination leads to increased signal-to-noise ratio by controlling the fluorophore photo-physics.1-2 Considering TPA, we have demonstrated that photo-thermal corruption due to pulse pile-up effect is largely solvent-mediated and a rather slow process which can be taken care of by simple intensity modulation of a pulse-train.3-4 We have recently shown how precise delay between pair of ultrafast pulses can lead to possible selective excitation in microscopy.5 We have also demonstrated how gigantic peak-power of a femto-second laser pulse (with rather low average power) leads to stable optical trapping of latex nano-particles which is otherwise impossible with continuous-wave excitation (at the same average power).6

    BibTeX: @article{goswamiSpatioTemporalControlMultiphoton2010,
     title = {Spatio-{{Temporal Control}} in {{Multiphoton Fluorescence Laser-Scanning Microscopy}}},
     author = {Goswami, Debabrata and Kumar De, Arijit},
     date = {2010-01},
     journaltitle = {Biophysical Journal},
     shortjournal = {Biophysical Journal},
     volume = {98},
     number = {3},
     pages = {586a},
     issn = {00063495},
     doi = {10/cwqtj2},
     url = {https://linkinghub.elsevier.com/retrieve/pii/S000634950904990X},
     urldate = {2019-08-14}
   }
   

8. Towards Using Molecular Ions as Qubits: Femtosecond Control of Molecular Fragmentation with Multiple Knobs. T. Goswami, D. K. Das, and D. Goswami, Pramana 75(6), 1065–1069 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: Non-resonant molecular fragmentation of n-propyl benzene with femtosecond laser pulses is dependent on the phase and polarization characteristics of the laser. We find that the effect of the chirp and polarization of the femtosecond pulse when applied simultaneously is mutually independent of each other, which makes chirp and polarization as useful ‘logic’ implementing knobs.

    BibTeX: @article{goswamiUsingMolecularIons2010,
     title = {Towards Using Molecular Ions as Qubits: {{Femtosecond}} Control of Molecular Fragmentation with Multiple Knobs},
     shorttitle = {Towards Using Molecular Ions as Qubits},
     author = {Goswami, Tapas and Das, Dipak K. and Goswami, Debabrata},
     date = {2010-12-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {75},
     number = {6},
     pages = {1065--1069},
     issn = {0973-7111},
     doi = {10/cf945s},
     url = {https://doi.org/10.1007/s12043-010-0190-9},
     urldate = {2019-08-14}
   }
   

9. Two-Photon Quantum Dot Excitation during Optical Trapping. L. Jauffred and L. B. Oddershede, Nano Letters 10(5), 1927–1930 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: A single CW infrared laser beam can simultaneously trap and excite an individual colloidal quantum dot. Though the laser light is relatively weak, the excitation occurs through two-photon absorption. This finding eliminates the demand for an excitation light source in addition to a trapping laser in nanoscale experiments with simultaneous force-manipulation and quantum dot visualization. Also, we demonstrate that optical trapping efficiencies of individual quantum dots do not correlate with their emission wavelength or physical size.

    BibTeX: @article{jauffredTwoPhotonQuantumDot2010,
     title = {Two-{{Photon Quantum Dot Excitation}} during {{Optical Trapping}}},
     author = {Jauffred, Liselotte and Oddershede, Lene B.},
     date = {2010-05-12},
     journaltitle = {Nano Letters},
     shortjournal = {Nano Lett.},
     volume = {10},
     number = {5},
     pages = {1927--1930},
     issn = {1530-6984},
     doi = {10/b49kwx},
     url = {https://doi.org/10.1021/nl100924z},
     urldate = {2019-10-01}
   }
   

10. Applying Genetic Algorithm Optimization to a Folded Geometry Acousto-Optic Modulated Spatial Pulse Shaper. A. Nag, P. A. Chaphekar, and D. Goswami, Review of Scientific Instruments 81(1), 013101 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: A folded geometry acousto-optic modulator spatial pulse shaper has been designed for shaping individual pulses from a high power amplified laser. The design preserves the capability of computer programmable amplitude and phase modulation of femtosecond laser pulses. An additional application of genetic algorithm optimization approach for compressing a stretched pulse is also demonstrated for such a pulse shaper. Spectrally and temporally resolved optical gating technique is used to characterize the shaped pulses.

     BibTeX: @article{nagApplyingGeneticAlgorithm2010,
      title = {Applying Genetic Algorithm Optimization to a Folded Geometry Acousto-Optic Modulated Spatial Pulse Shaper},
      author = {Nag, Amit and Chaphekar, Prasad A. and Goswami, Debabrata},
      date = {2010-01-01},
      journaltitle = {Review of Scientific Instruments},
      shortjournal = {Review of Scientific Instruments},
      volume = {81},
      number = {1},
      pages = {013101},
      issn = {0034-6748},
      doi = {10/ddkc77},
      url = {https://aip.scitation.org/doi/abs/10.1063/1.3276682},
      urldate = {2019-08-14}
    }
    

11. Polarization Induced Control of Single and Two-Photon Fluorescence. A. Nag and D. Goswami, The Journal of Chemical Physics 132(15), 154508 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Modulation of two-photon absorption, two-photon fluorescence (TPF), as well as single-photon fluorescence (SPF), is shown through incident laser polarization for different fluorescent dyes. TPF intensity increases as the polarization changes from circular to linear irrespective of the dye, though the intensity and wavelength dependent studies of two-photon polarization ratio for any particular dye (e.g., Rhodamine 6G) reveal the nature of their excited state. SPF intensity of IR125 and IR144 dyes increases as the polarization changes from linear to circular. Thus, polarization studies indicate that in case of TPF, there is a preference toward the linear component while in case of SPF, the preference is toward the circular component of the incident laser beam. I. INTRODUCTION

     BibTeX: @article{nagPolarizationInducedControl2010,
      title = {Polarization Induced Control of Single and Two-Photon Fluorescence},
      author = {Nag, Amit and Goswami, Debabrata},
      date = {2010-04-21},
      journaltitle = {The Journal of Chemical Physics},
      shortjournal = {J. Chem. Phys.},
      volume = {132},
      number = {15},
      pages = {154508},
      issn = {0021-9606},
      doi = {10/bdr2kh},
      url = {https://aip.scitation.org/doi/abs/10.1063/1.3386574},
      urldate = {2019-08-14}
    }
    

12. Coumarin Derived Chromophores in the Donor–Acceptor–Donor Format That Gives Fluorescence Enhancement and Large Two-Photon Activity in Presence of Specific Metal Ions. D. Ray, A. Nag, A. Jana, D. Goswami, and P. K. Bharadwaj, Inorganica Chimica Acta 363(12), 2824–2832 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Two coumarin derived dyes (compounds La and L) have been synthesized in high yields by Schiff base condensation. On probing with a femtosecond laser, none of these compounds show any two-photon activity in the wavelength range, 760–860nm. However, La in presence of Zn(II) and L in presence of Mg(II), exhibit large two-photon absorption as well as emission in the same wavelength range. Theoretical calculations at the B3LYP functional with 6-31G∗ and LanL2DZ mixed basis set under DFT formalism support experimental results.

     BibTeX: @article{rayCoumarinDerivedChromophores2010,
      title = {Coumarin Derived Chromophores in the Donor–Acceptor–Donor Format That Gives Fluorescence Enhancement and Large Two-Photon Activity in Presence of Specific Metal Ions},
      author = {Ray, Debdas and Nag, Amit and Jana, Atanu and Goswami, Debabrata and Bharadwaj, Parimal K.},
      date = {2010-10-15},
      journaltitle = {Inorganica Chimica Acta},
      shortjournal = {Inorganica Chimica Acta},
      series = {Special Volume: {{Dedicated}} to {{Professor Animesh Chakravorty}}},
      volume = {363},
      number = {12},
      pages = {2824--2832},
      issn = {0020-1693},
      doi = {10/c2k85x},
      url = {http://www.sciencedirect.com/science/article/pii/S0020169310002161},
      urldate = {2019-08-14}
    }
    

13. Precursor-Mediated Crystallization Process in Suspensions of Hard Spheres. T. Schilling, H. J. Schöpe, M. Oettel, G. Opletal, and I. Snook, Physical Review Letters 105(2), 025701 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: We report on a large scale computer simulation study of crystal nucleation in hard spheres. Through a combined analysis of real- and reciprocal-space data, a picture of a two-step crystallization process is supported: First, dense, amorphous clusters form which then act as precursors for the nucleation of well-ordered crystallites. This kind of crystallization process has been previously observed in systems that interact via potentials that have an attractive as well as a repulsive part, most prominently in protein solutions. In this context the effect has been attributed to the presence of metastable fluid-fluid demixing. Our simulations, however, show that a purely repulsive system (that has no metastable fluid-fluid coexistence) crystallizes via the same mechanism.

     BibTeX: @article{schillingPrecursorMediatedCrystallizationProcess2010,
      title = {Precursor-{{Mediated Crystallization Process}} in {{Suspensions}} of {{Hard Spheres}}},
      author = {Schilling, T. and Schöpe, H. J. and Oettel, M. and Opletal, G. and Snook, I.},
      date = {2010-07-08},
      journaltitle = {Physical Review Letters},
      shortjournal = {Phys. Rev. Lett.},
      volume = {105},
      number = {2},
      pages = {025701},
      doi = {10/drvm4d},
      url = {https://link.aps.org/doi/10.1103/PhysRevLett.105.025701},
      urldate = {2019-10-01}
    }
    

14. Spreading of Colloid Clusters in a Quasi-One-Dimensional Channel. X. Xu, B. Lin, B. Cui, A. R. Dinner, and S. A. Rice, The Journal of Chemical Physics 132(8), 084902 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: The effect of hydrodynamic interactions on the spreading of clusters of colloid particles in a quasi-one-dimensional channel is analyzed both experimentally and theoretically. An nn$n$-particle cluster spreading diffusion coefficient is defined, in terms of the displacement Δx(t)Δx(t)$\Delta x\left(t\right)$ in time tt$t$, by Dn≡⟨[∑ni=1Δxi(t)]2⟩/2ntDn≡⟨[∑ni=1Δxi(t)]2⟩/2nt$D_n\equiv ⟨{\left[{\sum }_{i=1}^n\Delta x_i\left(t\right)\right]}^2⟩/2nt$, where the average is taken over all groups of nn$n$ adjacent particles. Our study focuses on the nn$n$-dependence of DnDn$D_n$ with some attention to the dependence of DnDn$D_n$ on colloid packing fraction. We find that the ratio of DnDn$D_n$ to the infinite dilution self-diffusion coefficient D0SD0S$D_S^0$ increases as nn$n$ increases, eventually saturating for large nn$n$. The observed dependence of DnDn$D_n$ on nn$n$ is in satisfactory agreement with the predictions obtained from both Stokesian dynamics simulations and hydrodynamic calculations using the method of reflections.

     BibTeX: @article{xuSpreadingColloidClusters2010,
      title = {Spreading of Colloid Clusters in a Quasi-One-Dimensional Channel},
      author = {Xu, Xinliang and Lin, Binhua and Cui, Bianxiao and Dinner, Aaron R. and Rice, Stuart A.},
      date = {2010-02-25},
      journaltitle = {The Journal of Chemical Physics},
      shortjournal = {J. Chem. Phys.},
      volume = {132},
      number = {8},
      pages = {084902},
      issn = {0021-9606},
      doi = {10.1063/1.3330414},
      url = {https://aip.scitation.org/doi/full/10.1063/1.3330414},
      urldate = {2019-10-01}
    }
    

15. Colloidal Self-Assembly Meets Nanofabrication: From Two-Dimensional Colloidal Crystals to Nanostructure Arrays. J. Zhang, Y. Li, X. Zhang, and B. Yang, Advanced Materials 22(38), 4249–4269 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Self-assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self-assembly with nanofabrication techniques, two-dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as “colloidal lithography”, which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self-assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal-crystal-assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.

     BibTeX: @article{zhangColloidalSelfAssemblyMeets2010,
      title = {Colloidal {{Self-Assembly Meets Nanofabrication}}: {{From Two-Dimensional Colloidal Crystals}} to {{Nanostructure Arrays}}},
      shorttitle = {Colloidal {{Self-Assembly Meets Nanofabrication}}},
      author = {Zhang, Junhu and Li, Yunfeng and Zhang, Xuemin and Yang, Bai},
      date = {2010},
      journaltitle = {Advanced Materials},
      volume = {22},
      number = {38},
      pages = {4249--4269},
      issn = {1521-4095},
      doi = {10/bwn4hf},
      url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201000755},
      urldate = {2019-10-01}
    }
    

2009

1. Molecular Structure-Property Correlations from Optical Nonlinearity and Thermal-Relaxation Dynamics. I. Bhattacharyya, S. Priyadarshi, and D. Goswami, Chemical Physics Letters 469(1), 104–109 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We apply ultrafast single beam Z-scan technique to measure saturation absorption coefficients and nonlinear-refraction coefficients of primary alcohols at 1560nm. The nonlinear effects result from vibronic transitions and cubic nonlinear-refraction. To measure the pure total third-order nonlinear susceptibility, we removed thermal effects with a frequency optimized optical-chopper. Our measurements of thermal-relaxation dynamics of alcohols, from 1560nm thermal lens pump and 780nm probe experiments revealed faster and slower thermal-relaxation timescales, respectively, from conduction and convection. The faster timescale accurately predicts thermal-diffusivity, which decreases linearly with alcohol chain-lengths since thermal-relaxation is slower in heavier molecules. The relation between thermal-diffusivity and alcohol chain-length confirms structure-property relationship.

    BibTeX: @article{bhattacharyyaMolecularStructurepropertyCorrelations2009,
     title = {Molecular Structure-Property Correlations from Optical Nonlinearity and Thermal-Relaxation Dynamics},
     author = {Bhattacharyya, Indrajit and Priyadarshi, Shekhar and Goswami, Debabrata},
     date = {2009-02-03},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {469},
     number = {1},
     pages = {104--109},
     issn = {0009-2614},
     doi = {10/cpq233},
     url = {http://www.sciencedirect.com/science/article/pii/S0009261408017028},
     urldate = {2019-08-14}
   }
   

2. Adding New Dimensions to Laser-Scanning Fluorescence Microscopy. A. K. De and D. Goswami, Journal of Microscopy 233(2), 320–325 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We describe a novel method of optical imaging by exploiting simple ideas borrowed from pulsed optics. We show that the use of ultrafast pulsed one-photon excitation in laser-scanning fluorescence microscopy dramatically brings together several advantages offered by two widely used present day microscopic techniques, confocal and multi-photon fluorescence microscopy. The method appears as a novel tool in the context of laser-scanning fluorescence microscopy by having a ‘built-in’ 3D spatial resolution.

    BibTeX: @article{deAddingNewDimensions2009,
     title = {Adding New Dimensions to Laser-Scanning Fluorescence Microscopy},
     author = {De, A. K. and Goswami, D.},
     date = {2009},
     journaltitle = {Journal of Microscopy},
     volume = {233},
     number = {2},
     pages = {320--325},
     issn = {1365-2818},
     doi = {10/fd3jh9},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03122.x},
     urldate = {2019-08-14}
   }
   

3. A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy. A. K. De and D. Goswami, Journal of Microscopy 235(2), 119–123 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We describe a very simple but elegant approach to two-photon fluorescence signal enhancement by intensity modulation with immediate application in two-photon laser-scanning fluorescence microscopy. This method of enhancement shows potential application in any microscopic technique that result from non-linear photon absorption and plays a pivotal role in live cell imaging.

    BibTeX: @article{deSimpleTwistSignal2009,
     title = {A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy},
     author = {De, A. K. and Goswami, D.},
     date = {2009},
     journaltitle = {Journal of Microscopy},
     volume = {235},
     number = {2},
     pages = {119--123},
     issn = {1365-2818},
     doi = {10/ckpt72},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03176.x},
     urldate = {2019-08-14}
   }
   

4. Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination. A. K. De, D. Roy, A. Dutta, and D. Goswami, Applied Optics 48(31), G33–G37 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: Here we report how ultrafast pulsed illumination at low average power results in a stable three-dimensional (3D) optical trap holding latex nanoparticles which is otherwise not possible with continuous wave lasers at the same power level. The gigantic peak power of a femtosecond pulse exerts a huge instantaneous gradient force that has been predicted theoretically earlier and implemented for microsecond pulses in a different context by others. In addition, the resulting two-photon fluorescence allows direct observation of trapping events by providing intrinsic 3D resolution.

    BibTeX: @article{deStableOpticalTrapping2009,
     title = {Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination},
     author = {De, Arijit Kumar and Roy, Debjit and Dutta, Aveek and Goswami, Debabrata},
     date = {2009-11-01},
     journaltitle = {Applied Optics},
     shortjournal = {Appl. Opt., AO},
     volume = {48},
     number = {31},
     pages = {G33-G37},
     issn = {2155-3165},
     doi = {10/b9sxj4},
     url = {https://www.osapublishing.org/ao/abstract.cfm?uri=ao-48-31-G33},
     urldate = {2019-08-14}
   }
   

5. A Systematic Study on Fluorescence Enhancement under Single-photon Pulsed Illumination. A. K. De and D. Goswami, Journal of Fluorescence 19(5), 931–937 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We present a detailed study on fluorescence enhancement by ‘stroboscopic’ illumination with light pulses having duration ranging from few milliseconds to sub-picoseconds. We show how a delicate balance between pulse width and pulse repetition rate can result in an unprecedented fluorescence enhancement that has immediate applications in fluorescence imaging.

    BibTeX: @article{deSystematicStudyFluorescence2009,
     title = {A {{Systematic Study}} on {{Fluorescence Enhancement}} under {{Single-photon Pulsed Illumination}}},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-09-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {19},
     number = {5},
     pages = {931--937},
     issn = {1573-4994},
     doi = {10/bk2648},
     url = {https://doi.org/10.1007/s10895-009-0489-4},
     urldate = {2019-08-14}
   }
   

6. Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De and D. Goswami, Journal of Biomedical Optics 14(6), 064018 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: In multiphoton fluorescence laser-scanning microscopy, ultrafast laser pulses [i.e., light pulses having pulse width 1 ps (1 ps=10−12 s)] are commonly employed to circumvent the low-multiphoton absorption cross-sections of common fluorophores. Because of the broad overlapping two-photon absorption spectra of fluorophores and the large spectral bandwidth of a short pulse, simultaneous excitation of many fluorophores is common, which justifies a persistent demand for selective excitation of individual fluorophores. We describe the use of pulse-pair excitation with possibilities of controlling molecular fluorescence in laser-scanning microscopy and compare it with coherent control using pulse sequence [De and Goswami, "Coherent control in multiphoton fluorescence imaging," Proc. SPIE 7183, 71832B (2009)].

    BibTeX: @article{deUltrafastPulsepairControl2009,
     title = {Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-11},
     journaltitle = {Journal of Biomedical Optics},
     shortjournal = {JBO},
     volume = {14},
     number = {6},
     pages = {064018},
     issn = {1083-3668, 1560-2281},
     doi = {10/fvc8h7},
     url = {https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-14/issue-6/064018/Ultrafast-pulse-pair-control-in-multiphoton-fluorescence-laser-scanning-microscopy/10.1117/1.3268440.short},
     urldate = {2019-08-14}
   }
   

7. Local Viscosity of Binary Water+Glycerol Mixtures at Liquid/Liquid Interfaces Probed by Time-Resolved Surface Second Harmonic Generation. P. Fita, A. Punzi, and E. Vauthey, The Journal of Physical Chemistry C 113(48), 20705–20712 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: The excited-state relaxation of malachite green and brilliant green in solvents of various viscosity has been investigated at liquid/liquid interfaces and in bulk solutions by surface second harmonic generation and transient absorption spectroscopy. Mixtures of water and glycerol in various proportions have been used as solvents of variable viscosity. Transient absorption measurements in bulk revealed that both dyes are suitable as a probe of local viscosity for water+glycerol mixtures and that two of three processes following the optical excitation exhibit the same power dependence on solvent viscosity. This observation leads to assignment of the processes to a twist and twist-back of the aromatic rings attached to the central carbon atom of the dye. Therefore, identification of the intermediate state observed in the radiationless deactivation pathway with the twisted form of the dye has been supported. The time profiles of the second harmonic signal recorded at water+glycerol/dodecane interfaces have been found to be monoexponential at low dye concentrations (below 10−5 M) and biexponential at higher concentrations, and therefore the origin of the slower component has been attributed to the relaxation of dye aggregates adsorbed at the interface. The decay times measured at interfaces increased with increasing amount of glycerol in the mixture, but the rise was slower than in bulk solution. Therefore, the viscosity at the interfacial region, higher than that of the bulk solution, is mainly determined by structural modification of the solvent resulting from interactions between the two liquids that constitute the interface and addition of glycerol affects viscosity, only to a lesser extent. We have also shown that if the viscosity of the upper layer is much higher (at least 1 order of magnitude) than that of water or short alkanes, a slow-down of the relaxation is observed. This contradicts earlier findings and means that large amplitude motion of all three rings is involved in the deactivation of the excited molecule, but the rotation of the phenyl ring, which is smaller than the alkyl-substituted aniline groups, becomes a bottleneck for the relaxation in very viscous environments.

    BibTeX: @article{fitaLocalViscosityBinary2009,
     title = {Local {{Viscosity}} of {{Binary Water}}+{{Glycerol Mixtures}} at {{Liquid}}/{{Liquid Interfaces Probed}} by {{Time-Resolved Surface Second Harmonic Generation}}},
     author = {Fita, Piotr and Punzi, Angela and Vauthey, Eric},
     date = {2009-12-03},
     journaltitle = {The Journal of Physical Chemistry C},
     shortjournal = {J. Phys. Chem. C},
     volume = {113},
     number = {48},
     pages = {20705--20712},
     issn = {1932-7447},
     doi = {10/fjkvrb},
     url = {https://doi.org/10.1021/jp906676x},
     urldate = {2019-10-01}
   }
   

8. Control of Laser Induced Molecular Fragmentation of N-Propyl Benzene Using Chirped Femtosecond Laser Pulses. T. Goswami, S. K. Karthick Kumar, A. Dutta, and D. Goswami, Chemical Physics 360(1), 47–52 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We present the effect of chirping a femtosecond laser pulse on the fragmentation of n-propyl benzene. An enhancement of an order of magnitude for the relative yields of C3H3+ and C5H5+ in the case of negatively chirped pulses and C6H5+ in the case of positively chirped pulses with respect to the transform-limited pulse indicates that in some fragmentation channel, coherence of the laser field plays an important role. For the relative yield of all other heavier fragment ions, resulting from the interaction of the intense laser field with the molecule, there is no such enhancement effect with the sign of chirp, within experimental errors. The importance of the laser phase is further reinforced through a direct comparison of the fragmentation results with the second harmonic of the chirped laser pulse with identical bandwidth.

    BibTeX: @article{goswamiControlLaserInduced2009,
     title = {Control of Laser Induced Molecular Fragmentation of N-Propyl Benzene Using Chirped Femtosecond Laser Pulses},
     author = {Goswami, Tapas and Karthick Kumar, S. K. and Dutta, Aveek and Goswami, Debabrata},
     date = {2009-06-12},
     journaltitle = {Chemical Physics},
     shortjournal = {Chemical Physics},
     volume = {360},
     number = {1},
     pages = {47--52},
     issn = {0301-0104},
     doi = {10/b2h79c},
     url = {http://www.sciencedirect.com/science/article/pii/S0301010409001219},
     urldate = {2019-08-14}
   }
   

9. Femtosecond Spatio-Temporal Control. D. Goswami, T. Goswami, A. K. De, D. Roy, D. Das, and S. K. K. Kumar, International Conference on Optics and Photonics 4 (2009) [Abstract] [BibTeX]

   Abstract: We explore the simultaneous control of centre of mass and internal degrees of freedom of molecules. We have found that the fragmentation pattern of n-propyl benzene molecule is coherently affected by a femtosecond pulse with linear frequency modulation. The fragments (C3H3+, C5H5+) are enhanced with negatively chirped pulses while the C6H5+ fragment is reduced with positively chirped pulses. Similarly, using both continuous-wave (CW) and high repetition-rate femtosecond lasers, we present stable 3-dimensional trapping of 1μm polystyrene microspheres. We also stably trapped 100nm latex nanoparticles using the femtosecond mode-locked laser at a very low average power where the CW lasers cannot trap, demonstrating the significance of the high peak power of the fleeting temporal existence of the femtosecond pulses. Trapping was visualized through dark-field microscopy as well as through a noise free detection using two-photon fluorescence as a diagnostics tool due to its intrinsic 3-dimensional resolution. Simultaneous control of centre of mass and internal degrees of freedom of molecules would require coupling of various control parameters where we demonstrate that coupling of control parameters cannot be an apriority predictable determinant function.

    BibTeX: @article{goswamiFemtosecondSpatioTemporalControl2009,
     title = {Femtosecond {{Spatio-Temporal Control}}},
     author = {Goswami, Debabrata and Goswami, T and De, A K and Roy, D and Das, D and Kumar, S K Karthick},
     date = {2009},
     journaltitle = {International Conference on Optics and Photonics},
     pages = {4}
   }
   

10. Probing the Ultrafast Solution Dynamics of a Cyanine Dye in an Organic Solvent Interfaced with Water. T. Goswami, S. K. K. Kumar, A. Dutta, and D. Goswami, The Journal of Physical Chemistry B 113(51), 16332–16336 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Dependence of ultrafast dynamics on the excited state evolution and ground state recovery of a cyanine dye (IR125) in dichloromethane (DCM) solvent interfaced with neat water is presented. We use degenerate pump−probe transient absorption spectroscopy to show that the excited-state dynamics of the dye molecule is strongly dependent on the position of the measurements from bulk DCM solution to the solution near the water layer. The decay component of the transient corresponding to the excited state lifetime increases from bulk DCM solution to its interface with water. Such results show that the effect of the presence of water layer over the dye solution in DCM extends several micrometers, indicating the surfactant nature of the IR125 molecules, and provides us a measure of the penetration of water into the DCM layer. The initial ultrafast decay component (coherent spike) directly correlates to the pulse-width of our near-transform limited pulses used in these experiments. This approach of measuring the excited state decay of a dye across an immiscible liquid interface can provide important characteristics of microtransport across such interfaces.

     BibTeX: @article{goswamiProbingUltrafastSolution2009,
      title = {Probing the {{Ultrafast Solution Dynamics}} of a {{Cyanine Dye}} in an {{Organic Solvent Interfaced}} with {{Water}}},
      author = {Goswami, Tapas and Kumar, S. K. Karthick and Dutta, Aveek and Goswami, Debabrata},
      date = {2009-12-24},
      journaltitle = {The Journal of Physical Chemistry B},
      shortjournal = {J. Phys. Chem. B},
      volume = {113},
      number = {51},
      pages = {16332--16336},
      issn = {1520-6106},
      doi = {10/dc3b67},
      url = {https://doi.org/10.1021/jp903753u},
      urldate = {2019-08-14}
    }
    

11. Spectrally Resolved Photon Echo Spectroscopy of Zn(II), Co(II) and Ni(II)–Octaethyl Porphyrins. S. K. Karthick Kumar, V. Tiwari, T. Goswami, and D. Goswami, Chemical Physics Letters 476(1), 31–36 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Spectrally resolved femtosecond three-pulse photon echo signal from some metal–octaethyl porphyrins (OEPs) like Zn(II)–OEP, Ni(II)–OEP, Co(II)–OEP is reported. Excited state dynamics is studied by time evolving photon echo spectra for different values of coherence and population relaxation times. Dependence on the spectrally resolved photon echo spectra on varying metal center is analyzed. For all these metallo-porphyrins, the electronic relaxation timescale is found to be limited by our laser pulsewidth of 50fs whereas the timescale for intramolecular vibrational relaxation, occurring within the Q00 band was found to be over a picosecond for Co(II)–OEP and Ni(II)–OEP and within a picosecond for Zn(II)–OEP.

     BibTeX: @article{karthickkumarSpectrallyResolvedPhoton2009,
      title = {Spectrally Resolved Photon Echo Spectroscopy of {{Zn}}({{II}}), {{Co}}({{II}}) and {{Ni}}({{II}})–Octaethyl Porphyrins},
      author = {Karthick Kumar, S. K. and Tiwari, Vivek and Goswami, Tapas and Goswami, Debabrata},
      date = {2009-07-07},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {476},
      number = {1},
      pages = {31--36},
      issn = {0009-2614},
      doi = {10/fpmh7d},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409006666},
      urldate = {2019-08-14}
    }
    

12. Visible 20-Femtosecond Pulse Generation by Double-Pass Non-Collinear Optical Parametric Amplifier. S. K. K. Kumar, T. Goswami, I. Bhattacharyya, and D. Goswami, Current Science 96(11), 1496–1500 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: We report a new design and construction of a highpower, white light seeded double-pass non-collinear optical parametric amplifier (NOPA) in the visible wavelength using a single amplifier crystal. For its successful implementation, many important practical considerations are discussed in detail. Tunable femtosecond pulses were obtained with pulse widths less than 20 fs and characterized using frequency-resolved optical gating technique. The generated visible pulse, tunable from 490 to 740 nm from the NOPA, was further optimized by second harmonic and four-wave mixing signals.

     BibTeX: @article{kumarVisible20femtosecondPulse2009,
      title = {Visible 20-Femtosecond Pulse Generation by Double-Pass Non-Collinear Optical Parametric Amplifier},
      author = {Kumar, S. K. Karthick and Goswami, T. and Bhattacharyya, I. and Goswami, D.},
      date = {2009},
      journaltitle = {Current Science},
      volume = {96},
      number = {11},
      eprint = {24104778},
      eprinttype = {jstor},
      pages = {1496--1500},
      issn = {0011-3891},
      url = {https://www.jstor.org/stable/24104778},
      urldate = {2019-08-14}
    }
    

13. Towards Self-Replicating Materials of DNA-functionalized Colloids. M. E. Leunissen, R. Dreyfus, R. Sha, T. Wang, N. C. Seeman, D. J. Pine, and P. M. Chaikin, Soft Matter 5(12), 2422–2430 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: We report the first results of ongoing research that involves the creation of a new class of non-biological materials designed to self-replicate and, as a result, to grow exponentially. We propose a system design that exploits the strong specificity and thermal reversibility of the interactions between colloidal particles functionalized with complementary single-stranded DNA ‘sticky ends’. Here, we experimentally test the fundamentals of the different steps that constitute the self-replication scheme. First of all, we quantitatively study the equilibrium and kinetic aspects of the aggregation–dissociation behavior of the particles. We find that the dissociation transition is very sharp (∼1 °C) and that it occurs at unexpectedly low temperatures, with the dissociation temperature shifting further down when the fraction of sticky ends becomes smaller. The sharpness of the transition and its sensitivity to the sticky end fraction are important control parameters in our self-replication scheme. We further find that for our present purposes it is best to use a DNA construct with a double-stranded backbone, as this largely prevents unwanted hybridization events, such as secondary structure formation. The latter is seen to lead to peculiar aggregation kinetics, due to a competition between inter- and intra-particle hybridization. Finally, we show how one can obtain dual recognition at different temperatures by functionalizing a single particle species with two distinct DNA sequences and we demonstrate the formation of permanent bonds, using the chemical intercalator psoralen and long-wavelength UV exposure.

     BibTeX: @article{leunissenSelfreplicatingMaterialsDNAfunctionalized2009,
      title = {Towards Self-Replicating Materials of {{DNA-functionalized}} Colloids},
      author = {Leunissen, Mirjam E. and Dreyfus, Rémi and Sha, Roujie and Wang, Tong and Seeman, Nadrian C. and Pine, David J. and Chaikin, Paul M.},
      date = {2009-06-09},
      journaltitle = {Soft Matter},
      shortjournal = {Soft Matter},
      volume = {5},
      number = {12},
      pages = {2422--2430},
      issn = {1744-6848},
      doi = {10/cj2sn9},
      url = {https://pubs.rsc.org/en/content/articlelanding/2009/sm/b817679e},
      urldate = {2019-10-01}
    }
    

14. Protein Aggregation Kinetics, Mechanism, and Curve-Fitting: A Review of the Literature. A. M. Morris, M. A. Watzky, and R. G. Finke, Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics 1794(3), 375–397 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Protein aggregation is an important phenomenon that alternatively is part of the normal functioning of nature or, central to this review, has negative consequences via its hypothesized central role in neurodegenerative diseases. A key to controlling protein aggregation is understanding the mechanism(s) of protein aggregation. Kinetic studies, data curve-fitting, and analysis are, in turn, keys to rigorous mechanistic studies. The main goal of this review is to analyze and report on the primary literature contributions to protein aggregation kinetics, mechanism, and curve-fitting. Following a brief introduction, the multiple different physical methods that have been employed to follow protein aggregation are presented and briefly discussed. Next, key information on the starting proteins and especially the products, and any detectable intermediates, involved in protein aggregation are presented. This is followed by tabulation (in the Supporting information) and discussion (in the main text), of the many approaches in the literature striving to determine the kinetics and mechanism of protein aggregation. It is found that these approaches can be broadly divided into three categories: (i) kinetic and thermodynamic, (ii) empirical, and (iii) other approaches. The first two approaches are the main focus of the present contribution, their goal being curve-fitting the available kinetic data and obtaining quantitative rate constants characterizing the nucleation, growth, and any other parts of the overall aggregation process. The large literature of protein aggregation is distilled down to five classes of postulated mechanisms: i) the subsequent monomer addition mechanism, ii) the reversible association mechanism, iii) prion aggregation mechanisms, iv) an “Ockham’s razor”/minimalistic model first presented in 1997 and known as the Finke–Watzky 2-step model, and v) quantitative structure activity relationship models. These five classes of mechanisms are reviewed in detail in historical order; where possible corresponding kinetic equations, and fits to aggregation data via the proposed mechanisms, are analyzed and discussed. The five classes of mechanisms are then analyzed and discussed in terms of their similarities and differences to one another. Also included is a brief discussion of selected empirical approaches used to investigate protein aggregation. Three problem areas in the protein aggregation kinetic and mechanistic studies area are identified, and a Summary and Conclusions section is provided en route to moving the field forward towards the still unachieved goal of unequivocal elucidation of the mechanism(s) of protein aggregation.

     BibTeX: @article{morrisProteinAggregationKinetics2009,
      title = {Protein Aggregation Kinetics, Mechanism, and Curve-Fitting: {{A}} Review of the Literature},
      shorttitle = {Protein Aggregation Kinetics, Mechanism, and Curve-Fitting},
      author = {Morris, Aimee M. and Watzky, Murielle A. and Finke, Richard G.},
      date = {2009-03-01},
      journaltitle = {Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics},
      shortjournal = {Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics},
      volume = {1794},
      number = {3},
      pages = {375--397},
      issn = {1570-9639},
      doi = {10/djk6mq},
      url = {http://www.sciencedirect.com/science/article/pii/S1570963908003488},
      urldate = {2019-10-01}
    }
    

15. Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes. A. Nag and D. Goswami, Journal of Photochemistry and Photobiology A: Chemistry 206(2), 188–197 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: For a series of rhodamine dyes, two-photon absorption (TPA) and two-photon fluorescence (TPF) have been performed in different solvents. Solvent-dependent TPA spectra of these dyes were measured with open aperture z-scan method and compared to their respective single-photon spectra at equivalent energies. In the TPA spectra, relative peak intensities and positions are highly solvent dependent, which could be a result of vibronic couplings that depend on solvent environment. Measured TPA cross-sections of rhodamine dyes are consistently higher in nonpolar solvents. Certain complementary and similarity between TPA and TPF are also elucidated. Finally, a two-photon figure-of-merit is presented for these dyes in different solvents as a function of wavelength.

     BibTeX: @article{nagSolventEffectTwophoton2009,
      title = {Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes},
      author = {Nag, Amit and Goswami, Debabrata},
      date = {2009-08-15},
      journaltitle = {Journal of Photochemistry and Photobiology A: Chemistry},
      shortjournal = {Journal of Photochemistry and Photobiology A: Chemistry},
      volume = {206},
      number = {2},
      pages = {188--197},
      issn = {1010-6030},
      doi = {10/c4zdx8},
      url = {http://www.sciencedirect.com/science/article/pii/S1010603009002676},
      urldate = {2019-08-14}
    }
    

16. Two-Photon Cross-Section Measurements Using an Optical Chopper: Z-Scan and Two-Photon Fluorescence Schemes. A. Nag, A. K. De, and D. Goswami, Journal of Physics B: Atomic, Molecular and Optical Physics 42(6), 065103 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: An effective z-scan setup with a minimum thermal effect is shown for intensity-dependent measure of two-photon absorption (TPA) with high-repetition rate lasers. Use of an additional intensity modulation with an optical chopper provides enough blanking time for a high-repetition rate laser to yield equally accurate results in TPA measurements compared to a low repetition laser. Extension of this method of thermal effect management with an optical chopper to emission studies also results in good correspondence for two-photon cross-section measurements from either z-scan or two-photon fluorescence techniques. The method also significantly enhances two-photon fluorescence, which could be promising for multiphoton microscopy.

     BibTeX: @article{nagTwophotonCrosssectionMeasurements2009,
      title = {Two-Photon Cross-Section Measurements Using an Optical Chopper: Z-Scan and Two-Photon Fluorescence Schemes},
      shorttitle = {Two-Photon Cross-Section Measurements Using an Optical Chopper},
      author = {Nag, Amit and De, Arijit Kumar and Goswami, Debabrata},
      date = {2009-03-28},
      journaltitle = {Journal of Physics B: Atomic, Molecular and Optical Physics},
      volume = {42},
      number = {6},
      pages = {065103},
      issn = {0953-4075, 1361-6455},
      doi = {10/bhffqb},
      url = {http://stacks.iop.org/0953-4075/42/i=6/a=065103?key=crossref.bf9dc5810ad233241ea2c717000e14f8},
      urldate = {2018-12-10}
    }
    

17. Nanofabrication by Self-Assembly. G. A. Ozin, K. Hou, B. V. Lotsch, L. Cademartiri, D. P. Puzzo, F. Scotognella, A. Ghadimi, and J. Thomson, Materials Today 12(5), 12–23 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: The self-assembly paradigm in chemistry, physics and biology has matured scientifically over the past two-decades to a point of sophistication that one can begin to exploit its numerous attributes in nanofabrication. In what follows we will take a brief look at current thinking about self-assembly and with some recent examples taken from our own work examine how nanofabrication has benefited from self-assembly.

     BibTeX: @article{ozinNanofabricationSelfassembly2009,
      title = {Nanofabrication by Self-Assembly},
      author = {Ozin, Geoffrey A. and Hou, Kun and Lotsch, Bettina V. and Cademartiri, Ludovico and Puzzo, Daniel P. and Scotognella, Francesco and Ghadimi, Arya and Thomson, Jordan},
      date = {2009-05-01},
      journaltitle = {Materials Today},
      shortjournal = {Materials Today},
      volume = {12},
      number = {5},
      pages = {12--23},
      issn = {1369-7021},
      doi = {10/c7mc9z},
      url = {http://www.sciencedirect.com/science/article/pii/S1369702109701567},
      urldate = {2019-10-01}
    }
    

18. Acyclic Donor–Acceptor–Donor Chromophores for Large Enhancement of Two-Photon Absorption Cross-Section in the Presence of Mg(II), Ca(II) or Zn(II) Ions. D. Ray, A. Nag, D. Goswami, and P. K. Bharadwaj, Journal of Luminescence 129(3), 256–262 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Two new chromophores in the format, donor–acceptor–donor, have been synthesized in high yields from easily available starting materials. These compounds do not show any two-photon absorption (TPA) cross-section in the wavelength range, 780–900nm when probed by the Z-scan technique with a femtosecond laser. However, in presence of Zn(II), Ca(II) or Mg(II) ion, each compound gives exceptionally large TPA cross-section in the same wavelength range.

     BibTeX: @article{rayAcyclicDonorAcceptor2009,
      title = {Acyclic Donor–Acceptor–Donor Chromophores for Large Enhancement of Two-Photon Absorption Cross-Section in the Presence of {{Mg}}({{II}}), {{Ca}}({{II}}) or {{Zn}}({{II}}) Ions},
      author = {Ray, Debdas and Nag, Amit and Goswami, Debabrata and Bharadwaj, Parimal K.},
      date = {2009-03-01},
      journaltitle = {Journal of Luminescence},
      shortjournal = {Journal of Luminescence},
      volume = {129},
      number = {3},
      pages = {256--262},
      issn = {0022-2313},
      doi = {10.1016/j.jlumin.2008.10.005},
      url = {http://www.sciencedirect.com/science/article/pii/S0022231308002858},
      urldate = {2019-08-14}
    }
    

19. Mechanical Properties of a Giant Liposome Studied Using Optical Tweezers. Y. Shitamichi, M. Ichikawa, and Y. Kimura, Chemical Physics Letters 479(4), 274–278 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: The mechanical properties of a micrometer-sized giant liposome are studied by deforming it from the inside using dual-beam optical tweezers. As the liposome is extended, its shape changes from a sphere to a lemon shape, and finally, a tubular part is generated. The surface tension σ and the bending rigidity κ of the lipid membrane are obtained from the measured force–extension curve. In a one-phase liposome, it was found that σ increases as the charged component increases but κ remains approximately constant. In a two-phase liposome, the characteristic deformation and the force–extension curve differ from those observed for the one-phase liposome.

     BibTeX: @article{shitamichiMechanicalPropertiesGiant2009,
      title = {Mechanical Properties of a Giant Liposome Studied Using Optical Tweezers},
      author = {Shitamichi, Yoko and Ichikawa, Masatoshi and Kimura, Yasuyuki},
      date = {2009-09-17},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {479},
      number = {4},
      pages = {274--278},
      issn = {0009-2614},
      doi = {10/dfqrp5},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409009804},
      urldate = {2019-10-01}
    }
    

20. Optical Manipulation of Microtubules for Directed Biomolecule Assembly. C. Zoica Dinu, T. Chakrabarty, E. Lunsford, C. Mauer, J. Plewa, J. S. Dordick, and D. B. Chrisey, Soft Matter 5(20), 3818–3822 (2009) [PDF] [BibTeX]

     BibTeX: @article{zoicadinuOpticalManipulationMicrotubules2009,
      title = {Optical Manipulation of Microtubules for Directed Biomolecule Assembly},
      author = {Zoica~Dinu, Cerasela and Chakrabarty, Tania and Lunsford, Elaine and Mauer, Christopher and Plewa, Joseph and S.~Dordick, Jonathan and B.~Chrisey, Douglas},
      date = {2009},
      journaltitle = {Soft Matter},
      volume = {5},
      number = {20},
      pages = {3818--3822},
      doi = {10/brsq8p},
      url = {https://pubs.rsc.org/en/content/articlelanding/2009/sm/b904639a},
      urldate = {2019-10-01}
    }
    

2008

1. Propagation of Complex Shaped Ultrafast Pulses in Highly Optically Dense Samples. J. C. Davis, M. R. Fetterman, W. S. Warren, and D. Goswami, The Journal of Chemical Physics 128(15), 154312 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: We examine the propagation of shaped (amplitude- and frequency-modulated) ultrafast laser pulses through optically dense rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation all strongly depend on the laser pulse shape. For example, frequency swept pulses, which produce adiabatic passage in the optically thin limit (independent of the sign of the frequency sweep), behave unexpectedly in optically dense samples. Paraxial Maxwell optical Bloch equations can model our ultrafast pulse propagation results well and provide insight.

    BibTeX: @article{davisPropagationComplexShaped2008,
     title = {Propagation of Complex Shaped Ultrafast Pulses in Highly Optically Dense Samples},
     author = {Davis, J. C. and Fetterman, M. R. and Warren, W. S. and Goswami, D.},
     date = {2008-04-17},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {128},
     number = {15},
     pages = {154312},
     issn = {0021-9606},
     doi = {10/dcn637},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.2894871},
     urldate = {2019-08-14}
   }
   

2. Exploring the Nature of Photo-Damage in Two-photon Excitation by Fluorescence Intensity Modulation. A. K. De and D. Goswami, Journal of Fluorescence 19(2), 381 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: We investigate the relative photo-damage effects during one- and two-photon excitations and demonstrate that there exist fundamental differences in the damage induced by a high repetition rate laser as compared to that of a CW laser. This difference is evident from the degree of enhanced fluorescence intensity achieved by blanking the excitation with an optical chopper. Such an enhancement in fluorescence intensity provides better signal-to-noise ratio that could have immediate applications in multiphoton imaging of live specimens.

    BibTeX: @article{deExploringNaturePhotoDamage2008,
     title = {Exploring the {{Nature}} of {{Photo-Damage}} in {{Two-photon Excitation}} by {{Fluorescence Intensity Modulation}}},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2008-08-21},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {19},
     number = {2},
     pages = {381},
     issn = {1573-4994},
     doi = {10/ck4wnn},
     url = {https://doi.org/10.1007/s10895-008-0405-3},
     urldate = {2019-08-14}
   }
   

3. Attachment of Different Donor Groups to a Cryptand for Modulation of Two-Photon Absorption Cross-Section. A. Jana, S. Y. Jang, J.-Y. Shin, A. Kumar De, D. Goswami, D. Kim, and P. K. Bharadwaj, Chemistry – A European Journal 14(34), 10628–10638 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon absorption (TPA) properties of a laterally nonsymmetric aza cryptand with attached side arms have been investigated. This series of Schiff base derivatives supports the mechanistic approach for enhancing the TPA process, which is usually dictated by molecular geometry, π-bridging, delocalization length, and corresponding charge-transfer possibilities. The results described here suggest that on increasing the branching units, the TPA cross-section, σ(2), can be tuned to a larger value. The TPA activity is “switched on” when a metal atom enters the cavity and serves as a conduit of electronic delocalization. The σ(2) value increases as the donor strength increases. The maximum value is obtained on moving from the single-branched system to the nearly threefold symmetry. This serves as a useful synthetic strategy for designing novel octupolar molecules with high σ(2) values. Theoretical calculations at the B3LYP functional with the 6–31G* basis set under DFT formalism provide supporting evidence that the communication between the side arms through the metal d orbital and more ordered geometry of chromophores leads to a smaller HOMO–LUMO gap, which has a great influence upon the electronic properties of the molecules.

    BibTeX: @article{janaAttachmentDifferentDonor2008,
     title = {Attachment of {{Different Donor Groups}} to a {{Cryptand}} for {{Modulation}} of {{Two-Photon Absorption Cross-Section}}},
     author = {Jana, Atanu and Jang, So Young and Shin, Jae-Yoon and Kumar De, Arijit and Goswami, Debabrata and Kim, Dongho and Bharadwaj, Parimal K.},
     date = {2008},
     journaltitle = {Chemistry – A European Journal},
     volume = {14},
     number = {34},
     pages = {10628--10638},
     issn = {1521-3765},
     doi = {10/c5gh7k},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.200801396},
     urldate = {2019-08-14}
   }
   

4. Diaza-18-Crown-6 Based Chromophores for Modulation of Two-Photon Absorption Cross-Section by Metal Ions. A. Jana, A. Kumar De, A. Nag, D. Goswami, and P. K. Bharadwaj, Journal of Organometallic Chemistry 693(7), 1186–1194 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: Two chromophores with diaza-18-crown-6 as receptor have been synthesized in high yields. The electronic structure, one-photon absorption (OPA) spectra, and two-photon absorption (TPA) properties have been studied in detail. When no metal ion is added as input, both show negligible TPA cross-section (σ2). However, in the presence of Zn(II)/Cd(II)/Mg(II)/Ca(II) ion, each exhibits large TPA cross-section value. Binding of metal ion in the receptor increases the symmetric charge transfer leading to large σ2 values. Theoretical calculations at the B3LYP functional with 6-31G∗ and LanL2DZ mixed basis set under DFT formalism support experimental results.

    BibTeX: @article{janaDiaza18crown6BasedChromophores2008,
     title = {Diaza-18-Crown-6 Based Chromophores for Modulation of Two-Photon Absorption Cross-Section by Metal Ions},
     author = {Jana, Atanu and Kumar De, Arijit and Nag, Amit and Goswami, Debabrata and Bharadwaj, Parimal K.},
     date = {2008-04-01},
     journaltitle = {Journal of Organometallic Chemistry},
     shortjournal = {Journal of Organometallic Chemistry},
     volume = {693},
     number = {7},
     pages = {1186--1194},
     issn = {0022-328X},
     doi = {10/cdtg8k},
     url = {http://www.sciencedirect.com/science/article/pii/S0022328X08000466},
     urldate = {2019-08-14}
   }
   

5. Coded Nanoscale Self-Assembly. P. Samineni and D. Goswami, Pramana 71(6), 1345–1351 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate coded self-assembly in nanostructures using the code seeded at the component level through computer simulations. Defects or cavities occur in all natural assembly processes including crystallization and our simulations capture this essential aspect under surface minimization constraints for self-assembly. Our bottom-up approach to nanostructures would provide a new dimension towards nanofabrication and better understanding of defects and crystallization process.

    BibTeX: @article{samineniCodedNanoscaleSelfassembly2008,
     title = {Coded Nanoscale Self-Assembly},
     author = {Samineni, Prathyush and Goswami, Debabrata},
     date = {2008-12-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {71},
     number = {6},
     pages = {1345--1351},
     issn = {0973-7111},
     doi = {10/dhqk8m},
     url = {https://doi.org/10.1007/s12043-008-0188-8},
     urldate = {2019-08-14}
   }
   

2007

1. Metal Induced Enhancement of Fluorescence and Modulation of Two-Photon Absorption Cross-Section with a Donor–Acceptor–Acceptor–Donor Receptor. S. Das, A. Nag, K. K. Sadhu, D. Goswami, and P. K. Bharadwaj, Journal of Organometallic Chemistry 692(22), 4969–4977 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: A metal ion sensing fluorophore L that exhibits a large two-photon absorption cross-section has been synthesized in good yields. The influences of different metal ion inputs, on the one- and two-photon spectroscopic properties of L, have been investigated. The ligand itself does not show any fluorescence although in presence of a metal ion like Zn(II), Cd(II), Mg(II) or Ca(II), a ∼25 time enhancement of fluorescence is observed. The ligand with symmetrical “donor–acceptor–acceptor–donor” characteristics exhibits a large two-photon absorption cross-section measured by femtosecond open-aperture Z-scan technique at 880nm. However, presence of any of the above metal ions lowers its two-photon absorption cross-section (δ) to different extents at 880nm. Theoretical calculation carried out in DFT formalism on the ligand and its Zn(II) complex corroborate experimental results.

    BibTeX: @article{dasMetalInducedEnhancement2007,
     title = {Metal Induced Enhancement of Fluorescence and Modulation of Two-Photon Absorption Cross-Section with a Donor–Acceptor–Acceptor–Donor Receptor},
     author = {Das, Sanjib and Nag, Amit and Sadhu, Kalyan K. and Goswami, Debabrata and Bharadwaj, Parimal K.},
     date = {2007-10-15},
     journaltitle = {Journal of Organometallic Chemistry},
     shortjournal = {Journal of Organometallic Chemistry},
     volume = {692},
     number = {22},
     pages = {4969--4977},
     issn = {0022-328X},
     doi = {10/fkrn5p},
     url = {http://www.sciencedirect.com/science/article/pii/S0022328X07005244},
     urldate = {2019-08-14}
   }
   

2. Erratum to “High Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities” [Opt. Commun. 261 (2006) 158–162]. D. Goswami, Optics Communications 280(1), 236 (2007) [PDF] [BibTeX]

    BibTeX: @article{goswamiErratumHighSensitive2007,
     title = {Erratum to “{{High}} Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities” [{{Opt}}. {{Commun}}. 261 (2006) 158–162]},
     author = {Goswami, Debabrata},
     date = {2007-12},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {280},
     number = {1},
     pages = {236},
     issn = {00304018},
     doi = {10/bxb2kz},
     url = {https://linkinghub.elsevier.com/retrieve/pii/S0030401807007420},
     urldate = {2019-08-14}
   }
   

3. On the Practicality of Adiabatic Quantum Computing with Optical Schemes. D. Goswami, International Journal of Quantum Information 05(01n02), 179–188 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: A robust implementation of quantum logical gates for a multilevel system is possible through decoherence control under the quantum adiabatic method using simple phase modulated laser pulses. Selective population inversion and Hamiltonian evolution with time through ultrafast pulse shaping techniques essentially amount to adiabatic quantum computing (AQC) instead of the standard unitary transformation. An important aspect of the AQC model is in addressing the atomic or molecular ensemble and hence in robust implementation. We argue that experimental demonstrations of selective population transfer through adiabatic rapid passage form useful adiabatic quantum computing logic. Similarly, a simple Hadamard operation can be demonstrated with phase-modulated laser pulses. Finally, we present a framework to efficiently solve approximate Euclidean Traveling Salesman Problem (Approx-TSP) with bounded error in the AQC model. We present an efficient and intuitive encoding for Approx-TSP in a quantum computing paradigm. Optical approaches to quantum computing have the potential to be used in a distributive sense to defray the present caveat of limited resources and scalability. We present how we make use of such schemes towards practicality issues in AQC. As far as we know, our results are the first realistic demonstration of the possibility of using ensemble states for AQC in multilevel systems.

    BibTeX: @article{goswamiPracticalityAdiabaticQuantum2007,
     title = {On the Practicality of Adiabatic Quantum Computing with Optical Schemes},
     author = {Goswami, Debabrata},
     date = {2007-02-01},
     journaltitle = {International Journal of Quantum Information},
     shortjournal = {Int. J. Quantum Inform.},
     volume = {05},
     pages = {179--188},
     issn = {0219-7499},
     doi = {10/fkvv3x},
     url = {https://www.worldscientific.com/doi/abs/10.1142/S0219749907002621},
     urldate = {2019-08-14},
     issue = {01n02}
   }
   

4. Probing Coherence Aspects of Adiabatic Quantum Computation and Control. D. Goswami, The Journal of Chemical Physics 127(12), 124305 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: Quantum interference between multiple excitation pathways can be used to cancel the couplings to the unwanted, nonradiative channels resulting in robustly controlling decoherence through adiabatic coherent control approaches. We propose a useful quantification of the two-level character in a multilevel system by considering the evolution of the coherent character in the quantum system as represented by the off-diagonal density matrix elements, which switches from real to imaginary as the excitation process changes from being resonant to completely adiabatic. Such counterintuitive results can be explained in terms of continuous population exchange in comparison to no population exchange under the adiabatic condition.

    BibTeX: @article{goswamiProbingCoherenceAspects2007,
     title = {Probing Coherence Aspects of Adiabatic Quantum Computation and Control},
     author = {Goswami, Debabrata},
     date = {2007-09-25},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {127},
     number = {12},
     pages = {124305},
     issn = {0021-9606},
     doi = {10.1063/1.2768954},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.2768954},
     urldate = {2019-08-14}
   }
   

5. One-Pot Synthesis of Core-Modified Rubyrin, Octaphyrin, and Dodecaphyrin: Characterization and Nonlinear Optical Properties. R. Kumar, R. Misra, T. K. Chandrashekar, A. Nag, D. Goswami, E. Suresh, and C. H. Suresh, European Journal of Organic Chemistry 2007(27), 4552–4562 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: Modified 26π rubyrin, 36π octaphyrin, and 54π dodecaphyrin systems have been synthesized in moderately good yields through acid-catalyzed condensations of terthiophene diols and tripyrranes. The product distributions are decided both by the acid catalyst concentration and by the nature of the meso substituents. For example, a new isomer of [26]hexaphyrin(1.1.1.1.0.0) (rubyrin) was obtained with 0.3 equiv. of p-toluenesulfonic acid, when the meso substituent was mesityl in at least one of the precursors. A change of the mesityl substituent for a p-methoxy substituent in terthiophene diol resulted in the formation of a [3 + 3 + 3 + 3] condensation product – [54]dodecaphyrin(1.1.1.1.0.0.1.1.1.1.0.0) – in addition to the expected rubyrin. Furthermore, an increase in the acid concentration to 0.6 equiv. resulted in the formation of a new [36]octaphyrin(1.1.1.1.1.1.0.0), in addition to the rubyrin and dodecaphyrin. A single-crystal X-ray analysis of octaphyrin represents the first example of a planar conformation of an octaphyrin with six meso links. In rubyrin 19, one thiophene ring, opposite to the terthiophene subunit, is inverted, while in octaphyrin 30 one pyrrole ring and two thiophene rings are inverted. The various conformational possibilities tested for the unsubstituted dodecaphyrin 28, at semiempirical level, suggest that the most stable conformation is a figure-eight. The final geometry optimization of figure-eight dodecaphyrin was done at the B3LYP/6-31G* level of DFT. Octaphyrins and dodecaphyrins bind trifluoroacetate anion effectively in their diprotonated forms, the binding constants (K) being 638 M–1 for dodecaphyrin 28, and 415 M–1 for octaphyrin 30. Electrochemical data reveal HOMO destabilization with increasing π electron conjugation, consistently with the large red shifts of the absorption bands. Preliminary studies on the use of these expanded porphyrins as third-order NLO materials were followed by measurements of their two-photon absorption (TPA) cross-sections [σ(2)]. The σ(2) values increase upon going from the 26π rubyrins to the 54π dodecaphyrins, confirming our earlier observation that increases in π-conjugated electrons increase the TPA values.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

    BibTeX: @article{kumarOnePotSynthesisCoreModified2007,
     title = {One-{{Pot Synthesis}} of {{Core-Modified Rubyrin}}, {{Octaphyrin}}, and {{Dodecaphyrin}}: {{Characterization}} and {{Nonlinear Optical Properties}}},
     shorttitle = {One-{{Pot Synthesis}} of {{Core-Modified Rubyrin}}, {{Octaphyrin}}, and {{Dodecaphyrin}}},
     author = {Kumar, Rajeev and Misra, Rajneesh and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata and Suresh, Eringathodi and Suresh, Cherumuttathu H.},
     date = {2007},
     journaltitle = {European Journal of Organic Chemistry},
     volume = {2007},
     number = {27},
     pages = {4552--4562},
     issn = {1099-0690},
     doi = {10/bwctt3},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/ejoc.200700466},
     urldate = {2019-08-14}
   }
   

6. The Nanoparticle–Protein Complex as a Biological Entity; a Complex Fluids and Surface Science Challenge for the 21st Century. I. Lynch, T. Cedervall, M. Lundqvist, C. Cabaleiro-Lago, S. Linse, and K. A. Dawson, Advances in Colloid and Interface Science 134–135, 167–174 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: The major aim of our current work is to develop a deep understanding of biological effects of nanoparticles and how these effects are mediated by proteins that are adsorbed on the nanoparticles under different biological circumstances. Due to their small size, nanoparticles have distinct properties compared to the bulk form of the same materials, and these properties are rapidly revolutionizing many areas of medicine and technology. However, relatively little is known about the interaction of nanoscale objects with biological systems, as this requires quite different concepts from more established nanoscience. Thus, we have argued that in a biological fluid, proteins associate with nanoparticles, and it is the amount and presentation of the proteins on the surface rather than the particles themselves that are the cause of numerous biological responses. It is this outer layer of proteins that is seen by the biological cells, and leads to their responses. We are developing novel techniques to identify and quantify the proteins that are consistently associated with nanoparticles, as a function of the nanoparticle size, shape, and surface properties, and to correlate the adsorbed protein identities with their association and dissociation rates to and from the nanoparticles. We also seek to understand the degree of conformational change that they undergo upon adsorption to the nanoparticles. In essence, we wish to create “epitope maps” of the protein corona that surrounds nanoparticles in biological solutions, as it is the particle–protein complex that is the biologically active entity.

    BibTeX: @article{lynchNanoparticleProteinComplex2007,
     title = {The Nanoparticle–Protein Complex as a Biological Entity; a Complex Fluids and Surface Science Challenge for the 21st Century},
     author = {Lynch, Iseult and Cedervall, Tommy and Lundqvist, Martin and Cabaleiro-Lago, Celia and Linse, Sara and Dawson, Kenneth A.},
     date = {2007-10-31},
     journaltitle = {Advances in Colloid and Interface Science},
     shortjournal = {Advances in Colloid and Interface Science},
     series = {Surface Forces: Wetting Phenomena, Membrane Separation, Rheology. {{Topical}} Issue in Honour of {{Victor Starov}}},
     volume = {134--135},
     pages = {167--174},
     issn = {0001-8686},
     doi = {10/chq8ff},
     url = {http://www.sciencedirect.com/science/article/pii/S000186860700067X},
     urldate = {2019-10-01}
   }
   

7. A Sensitive Technique for Two-Photon Absorption Measurements: Towards Higher Resolution Microscopy. A. Nag, A. K. De, and D. Goswami, Journal of Physics: Conference Series 80, 012034 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: High repetition rate (HRR) lasers are essential in multiphoton microscopy for satisfactory signal to noise at low average powers. However, HRR lasers generate thermal distortions in samples even with the slightest single photon absorption. Using an optical chopper with HRR lasers ("blanking") we demonstrate a femtosecond z-scan setup that effectively eliminates thermal as well as small linear absorption effects and precisely measures two-photon absorption (TPA) cross-sections of chromophores. Accurate measurement of TPA cross-sections in biologically relevant chromophores is especially important since the TPA spectrum is considerably different in regions with even minute linear absorption. Such blanking measurements with chopper also show enhanced fluorescence efficiency of the chromophores.

    BibTeX: @article{nagSensitiveTechniqueTwoPhoton2007,
     title = {A {{Sensitive Technique}} for {{Two-Photon Absorption Measurements}}: {{Towards Higher Resolution Microscopy}}},
     shorttitle = {A {{Sensitive Technique}} for {{Two-Photon Absorption Measurements}}},
     author = {Nag, Amit and De, Arijit Kr and Goswami, Debabrata},
     date = {2007-09},
     journaltitle = {Journal of Physics: Conference Series},
     shortjournal = {J. Phys.: Conf. Ser.},
     volume = {80},
     pages = {012034},
     issn = {1742-6596},
     doi = {10/bwjg5v},
     url = {https://doi.org/10.1088%2F1742-6596%2F80%2F1%2F012034},
     urldate = {2019-08-14}
   }
   

2006

1. Dependence of Adiabatic Population Transfer on Pulse Profile. S. Dasgupta, T. Kushwaha, and D. Goswami, Pramana 66(6), 999 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Control of population transfer by rapid adiabatic passage has been an established technique wherein the exact amplitude profile of the shaped pulse is considered to be insignificant. We study the effect of ultrafast shaped pulses for two-level systems, by density-matrix approach. However, we find that adiabaticity depends simultaneously on pulse profile as well as the frequency modulation under non-resonant conditions

    BibTeX: @article{dasguptaDependenceAdiabaticPopulation2006,
     title = {Dependence of Adiabatic Population Transfer on Pulse Profile},
     author = {Dasgupta, S. and Kushwaha, T. and Goswami, D.},
     date = {2006-06-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {66},
     number = {6},
     pages = {999},
     issn = {0973-7111},
     doi = {10/bsg5fd},
     url = {https://doi.org/10.1007/BF02708454},
     urldate = {2019-08-14}
   }
   

2. Zinc(II)- and Copper(I)-Mediated Large Two-Photon Absorption Cross Sections in a Bis-cinnamaldiminato Schiff Base. S. Das, A. Nag, D. Goswami, and P. K. Bharadwaj, Journal of the American Chemical Society 128(2), 402–403 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: A Schiff base ligand has been synthesized by condensing 1,2-diaminobenzene with 4-(dimethylamino)cinnamaldehyde to give a donor−π-acceptor−π-donor system which does not show any two-photon absorption cross section but which does, upon complexation with Zn(II) or Cu(I), exhibit very high two-photon absorption cross sections.

    BibTeX: @article{dasZincIICopper2006,
     title = {Zinc({{II}})- and {{Copper}}({{I}})-{{Mediated Large Two-Photon Absorption Cross Sections}} in a {{Bis-cinnamaldiminato Schiff Base}}},
     author = {Das, Sanjib and Nag, Amit and Goswami, Debabrata and Bharadwaj, Parimal K.},
     date = {2006-01-01},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {128},
     number = {2},
     pages = {402--403},
     issn = {0002-7863},
     doi = {10/bccmmp},
     url = {https://doi.org/10.1021/ja056771q},
     urldate = {2019-08-14}
   }
   

3. Adiabatic Quantum Computation: Coherent Control Back Action. D. Goswami, AIP Conference Proceedings 864(1), 273–294 (2006) [PDF] [BibTeX]

    BibTeX: @article{goswamiAdiabaticQuantumComputation2006,
     title = {Adiabatic {{Quantum Computation}}: {{Coherent Control Back Action}}},
     shorttitle = {Adiabatic {{Quantum Computation}}},
     author = {Goswami, Debabrata},
     date = {2006-11-15},
     journaltitle = {AIP Conference Proceedings},
     shortjournal = {AIP Conference Proceedings},
     volume = {864},
     number = {1},
     pages = {273--294},
     issn = {0094-243X},
     doi = {10/dg98nw},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.2400899},
     urldate = {2019-08-14}
   }
   

4. High Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities. D. Goswami, Optics Communications 261(1), 158–162 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Accurate knowledge of absorption coefficient of a sample is a prerequisite for measuring the third-order optical nonlinearity of materials, which can be a serious limitation for unknown samples. We introduce a method, which measures both the absorption coefficient and the third-order optical nonlinearity of materials with high sensitivity in a single experimental arrangement. We use a dual-beam pump–probe experiment and conventional single-beam z-scan under different conditions to achieve this goal with communication relevant wavelength. We also demonstrate a counterintuitive coupling of the non-interacting probe-beam with the pump-beam in pump–probe z-scan experiment.

    BibTeX: @article{goswamiHighSensitiveMeasurements2006,
     title = {High Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities},
     author = {Goswami, Debabrata},
     date = {2006-05-01},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {261},
     number = {1},
     pages = {158--162},
     issn = {0030-4018},
     doi = {10/ds4qqp},
     url = {http://www.sciencedirect.com/science/article/pii/S0030401805012903},
     urldate = {2019-08-14}
   }
   

5. Second-Harmonic Generation from Magnetic Metamaterials. M. W. Klein, C. Enkrich, M. Wegener, and S. Linden, Science 313(5786), 502–504 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: We observe second-harmonic generation from metamaterials composed of split-ring resonators excited at 1.5-micrometer wavelength. Much larger signals are detected when magnetic-dipole resonances are excited, as compared with purely electric-dipole resonances. The experiments are consistent with calculations based on the magnetic component of the Lorentz force exerted on metal electrons—an intrinsic second-harmonic generation mechanism that plays no role in natural materials. This unusual mechanism becomes relevant in our work as a result of the enhancement and the orientation of the local magnetic fields associated with the magnetic-dipole resonances of the split-ring resonators. An array of split gold rings produces a current that exhibits a nonlinear magnetic response to infrared light, confirming predictions. An array of split gold rings produces a current that exhibits a nonlinear magnetic response to infrared light, confirming predictions.

    BibTeX: @article{kleinSecondHarmonicGenerationMagnetic2006,
     title = {Second-{{Harmonic Generation}} from {{Magnetic Metamaterials}}},
     author = {Klein, Matthias W. and Enkrich, Christian and Wegener, Martin and Linden, Stefan},
     date = {2006-07-28},
     journaltitle = {Science},
     volume = {313},
     number = {5786},
     eprint = {16873661},
     eprinttype = {pmid},
     pages = {502--504},
     issn = {0036-8075, 1095-9203},
     doi = {10/d4qxbj},
     url = {https://science.sciencemag.org/content/313/5786/502},
     urldate = {2019-10-01}
   }
   

6. 22π Smaragdyrin Molecular Conjugates with Aromatic Phenylacetylenes and Ferrocenes: Syntheses, Electrochemical, and Photonic Properties. R. Misra, R. Kumar, T. K. Chandrashekar, C. H. Suresh, A. Nag, and D. Goswami, Journal of the American Chemical Society 128(50), 16083–16091 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Syntheses, spectroscopic, electrochemical, and third-order nonlinear optical susceptibilities of a series of 22π smaragdyrins and their corresponding Rh(I) derivatives bearing phenylacetylene substituents and ferrocene-containing substituents are reported. The synthetic strategy involved a [3 + 2] acid-catalyzed oxidative coupling reaction of the appropriate dipyrromethane and oxatripyrrane. The desired meso substituents, such as phenylacetylenylphenyl and the ferrocenes, were incorporated to the dipyrromethane unit prior to the oxidative coupling reaction. The optical absorption, emission characteristics, and the quantum yield of the smaragdyrin conjugates depends on the nature of the substituent, nature of linker group, and the spacer length. Theoretical studies at the DFT level suggest high delocalization of electrons confined to only four of the five available heterocyclic rings for the free bases. However, upon Rh(I) metalation, the π-electron delocalization is extended to all the heterocyclic rings. The two-photon absorption cross section (TPA) values σ(2) measured through the open aperture Z-scan method, increases linearly with enhanced π-electron delocalization for the smaragdyrins containing phenylacetylene substituents. The meta branching of substituents decreases σ(2) values. Introduction of Rh(I) to the smaragdyrin cavity enhances the σ(2) values by about 3−10 orders of magnitude, attributed to the increased aromatic character upon Rh(I) insertion. The calculated molecular electrostatic potential (MESP) and harmonic oscillator model of aromaticity (HOMA) for the free bases and the Rh(I) derivatives justifies such a conclusion. A linear correlation observed for the second oxidation potential of Rh(I) derivatives and corresponding free bases also support the increased aromaticity upon Rh(I) insertion. The electrochemical data for ferrocene-containing smaragdyrins reveal easier ring oxidation by about 50−130 mV and harder ferrocene oxidation by 40−180 mV suggesting electron-donating nature of the ferrocene upon linking with the smaragdyrin π system. The TPA cross section value of 88782 GM observed for 5g represents one of the highest values known for a metalloexpanded porphyrin derivative.

    BibTeX: @article{misra22pSmaragdyrinMolecular2006,
     title = {22π {{Smaragdyrin Molecular Conjugates}} with {{Aromatic Phenylacetylenes}} and {{Ferrocenes}}:\, {{Syntheses}}, {{Electrochemical}}, and {{Photonic Properties}}},
     shorttitle = {22π {{Smaragdyrin Molecular Conjugates}} with {{Aromatic Phenylacetylenes}} and {{Ferrocenes}}},
     author = {Misra, Rajneesh and Kumar, Rajeev and Chandrashekar, Tavarekere K. and Suresh, C. H. and Nag, Amit and Goswami, Debabrata},
     date = {2006-12-01},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {128},
     number = {50},
     pages = {16083--16091},
     issn = {0002-7863},
     doi = {10/ds2r2p},
     url = {https://doi.org/10.1021/ja0628295},
     urldate = {2019-08-14}
   }
   

7. Modified (22π) Smaragdyrins with Large Two-Photon Absorption Cross Section: A Structure Function Correlation. R. Misra, R. Kumar, T. K. Chandrashekar, A. Nag, and D. Goswami, Organic Letters 8(4), 629–631 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon absorption (TPA) cross-section values for a series of 22π smaragdyrins bearing phenylacetylenylphenyl and [(phenylacetylenyl)phenylacetylenyl]phenyl meso links and their Rh(I) derivatives are reported.

    BibTeX: @article{misraModified22pSmaragdyrins2006,
     title = {Modified (22π) {{Smaragdyrins}} with {{Large Two-Photon Absorption Cross Section}}:\, {{A Structure Function Correlation}}},
     shorttitle = {Modified (22π) {{Smaragdyrins}} with {{Large Two-Photon Absorption Cross Section}}},
     author = {Misra, Rajneesh and Kumar, Rajeev and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata},
     date = {2006-02-01},
     journaltitle = {Organic Letters},
     shortjournal = {Org. Lett.},
     volume = {8},
     number = {4},
     pages = {629--631},
     issn = {1523-7060},
     doi = {10/dhmkht},
     url = {https://doi.org/10.1021/ol052809s},
     urldate = {2019-08-14}
   }
   

8. Structure Property Correlations in Alcohols through Two-Photon Absorption Cross-Section Measurements. A. Nag, S. Singh, and D. Goswami, Chemical Physics Letters 430(4), 420–423 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon absorption (TPA) cross-sections of neat alcohols are shown to be a femtosecond laser measurable property with useful structure property correlations that are directly correlated to the self-phase modulation of the alcohol in question. The amount of self-phase modulation is shown to be a molecular structure dependent property. The real and the imaginary components of the second-order hyperpolarizability are thus shown to be interrelated. Such TPA measurements prove that it is not possible to predict two-photon absorption properties by simple doubling the wavelengths of one-photon absorption spectra.

    BibTeX: @article{nagStructurePropertyCorrelations2006,
     title = {Structure Property Correlations in Alcohols through Two-Photon Absorption Cross-Section Measurements},
     author = {Nag, Amit and Singh, Sherdeep and Goswami, Debabrata},
     date = {2006-10-30},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {430},
     number = {4},
     pages = {420--423},
     issn = {0009-2614},
     doi = {10/dbmk87},
     url = {http://www.sciencedirect.com/science/article/pii/S0009261406013091},
     urldate = {2019-08-14}
   }
   

9. Nanowire Photonics. P. J. Pauzauskie and P. Yang, Materials Today 9(10), 36–45 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: The development of integrated electronic circuitry ranks among the most disruptive and transformative technologies of the 20th century. Even though integrated circuits are ubiquitous in modern life, both fundamental and technical constraints will eventually test the limits of Moore’s law. Nanowire photonic circuitry constructed from myriad one-dimensional building blocks offers numerous opportunities for the development of next-generation optical information processors and spectroscopy. However, several challenges remain before the potential of nanowire building blocks is fully realized. We cover recent advances in nanowire synthesis, characterization, lasing, integration, and the eventual application to relevant technical and scientific questions.

    BibTeX: @article{pauzauskieNanowirePhotonics2006,
     title = {Nanowire Photonics},
     author = {Pauzauskie, Peter J. and Yang, Peidong},
     date = {2006-10-01},
     journaltitle = {Materials Today},
     shortjournal = {Materials Today},
     volume = {9},
     number = {10},
     pages = {36--45},
     issn = {1369-7021},
     doi = {10/cs3g73},
     url = {http://www.sciencedirect.com/science/article/pii/S1369702106716522},
     urldate = {2019-10-01}
   }
   

10. Aromatic Core Modified Decaphyrins with the Largest Two-Photon Absorption Cross-Sections: Syntheses and Characterization. H. Rath, V. Prabhuraja, T. K. Chandrashekar, A. Nag, D. Goswami, and B. S. Joshi, Organic Letters 8(11), 2325–2328 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: Core-modified aromatic decaphyrins with 42π conjugated electrons exhibit the highest two-photon absorption cross-section value (σ2 = 108 000 GM) known for any organic molecule, suggesting possible device applications in the field of nonlinear optics.

     BibTeX: @article{rathAromaticCoreModified2006,
      title = {Aromatic {{Core Modified Decaphyrins}} with the {{Largest Two-Photon Absorption Cross-Sections}}:\, {{Syntheses}} and {{Characterization}}},
      shorttitle = {Aromatic {{Core Modified Decaphyrins}} with the {{Largest Two-Photon Absorption Cross-Sections}}},
      author = {Rath, Harapriya and Prabhuraja, Viswanathan and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata and Joshi, Bhawani S.},
      date = {2006-05-01},
      journaltitle = {Organic Letters},
      shortjournal = {Org. Lett.},
      volume = {8},
      number = {11},
      pages = {2325--2328},
      issn = {1523-7060},
      doi = {10/cwgk39},
      url = {https://doi.org/10.1021/ol060622a},
      urldate = {2019-08-14}
    }
    

11. Calibration of Optical Tweezers with Positional Detection in the Back Focal Plane. S. F. Tolić-Nørrelykke, E. Schäffer, J. Howard, F. S. Pavone, F. Jülicher, and H. Flyvbjerg, Review of Scientific Instruments 77(10), 103101 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: We explain and demonstrate a new method of force and position calibrations for optical tweezers with back-focal-plane photodetection. The method combines power spectral measurements of thermal motion and the response to a sinusoidal motion of a translation stage. It consequently does not use the drag coefficient of the trapped object as an input. Thus, neither the viscosity, nor the size of the trapped object, nor its distance to nearby surfaces needs to be known. The method requires only a low level of instrumentation and can be applied in situ in all spatial dimensions. It is both accurate and precise: true values are returned, with small error bars. We tested this experimentally, near and far from surfaces in the lateral directions. Both position and force calibrations were accurate to within 3%. To calibrate, we moved the sample with a piezoelectric translation stage, but the laser beam could be moved instead, e.g., by acousto-optic deflectors. Near surfaces, this precision requires an improved formula for the hydrodynamical interaction between an infinite plane and a microsphere in nonconstant motion parallel to it. We give such a formula.

     BibTeX: @article{tolic-norrelykkeCalibrationOpticalTweezers2006,
      title = {Calibration of Optical Tweezers with Positional Detection in the Back Focal Plane},
      author = {Tolić-Nørrelykke, Simon F. and Schäffer, Erik and Howard, Jonathon and Pavone, Francesco S. and Jülicher, Frank and Flyvbjerg, Henrik},
      date = {2006-10-01},
      journaltitle = {Review of Scientific Instruments},
      shortjournal = {Review of Scientific Instruments},
      volume = {77},
      number = {10},
      pages = {103101},
      issn = {0034-6748},
      doi = {10/dzq7fk},
      url = {https://aip.scitation.org/doi/full/10.1063/1.2356852},
      urldate = {2019-10-01}
    }
    

12. Optical Trapping and Light-Induced Agglomeration of Gold Nanoparticle Aggregates. Y. Zhang, C. Gu, A. M. Schwartzberg, S. Chen, and J. Z. Zhang, Physical Review B 73(16), 165405 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: This paper demonstrates the optical trapping of micron-sized gold nanoparticle aggregates (GNAs) with a TEM00 mode laser at 532nm and reports the observation of an unusual light-induced agglomeration phenomenon that occurs besides the trapping of the GNAs. The observed agglomerate has a 60–100μm donut-shaped metal microstructure with the rate of formation dependent on the laser power used. Citrate capped gold nanoparticles also show light-induced agglomeration, yielding different sized microstructures from those produced with GNAs. While the observed trapping can be explained by a model including the optical radiation and radiometric forces, the light-induced agglomeration cannot be explained by these two forces alone as the size of the agglomerate is much greater than the waist of the Gaussian beam used in the optical trapping. We attribute the additional cause of the light-induced agglomeration to ion detachment from the surface of the nanoparticles (aggregates) due to light illumination or heating. This is supported by the observation of reversible electrical conductivity changes of the solution of the nanoparticles (aggregates) upon laser illumination or direct heating. Light-induced agglomeration can be useful in the design and fabrication of microstructures from nanomaterials for various device applications.

     BibTeX: @article{zhangOpticalTrappingLightinduced2006,
      title = {Optical Trapping and Light-Induced Agglomeration of Gold Nanoparticle Aggregates},
      author = {Zhang, Yi and Gu, Claire and Schwartzberg, Adam M. and Chen, Shaowei and Zhang, Jin Z.},
      date = {2006-04-06},
      journaltitle = {Physical Review B},
      shortjournal = {Phys. Rev. B},
      volume = {73},
      number = {16},
      pages = {165405},
      doi = {10/bpw2d7},
      url = {https://link.aps.org/doi/10.1103/PhysRevB.73.165405},
      urldate = {2019-10-01}
    }
    

2005

1. Adiabatic Quantum Computing with Phase Modulated Laser Pulses. D. Goswami, Journal of Physics A: Mathematical and General 38(38), L615–L626 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: Implementation of quantum logical gates for multilevel systems is demonstrated through decoherence control under the quantum adiabatic method using simple phase modulated laser pulses. We make use of selective population inversion and Hamiltonian evolution with time to achieve such goals robustly instead of the standard unitary transformation language.

    BibTeX: @article{goswamiAdiabaticQuantumComputing2005,
     title = {Adiabatic Quantum Computing with Phase Modulated Laser Pulses},
     author = {Goswami, Debabrata},
     date = {2005-09-23},
     journaltitle = {Journal of Physics A: Mathematical and General},
     shortjournal = {J. Phys. A: Math. Gen.},
     volume = {38},
     number = {38},
     pages = {L615-L626},
     issn = {0305-4470, 1361-6447},
     doi = {10/cf95fb},
     url = {http://stacks.iop.org/0305-4470/38/i=38/a=L02?key=crossref.595c46dd082aae283e104e33a2aafff9},
     urldate = {2019-08-14}
   }
   

2. Multiphoton Coherent Control in Complex Systems. D. Goswami, Journal of Optics B: Quantum and Semiclassical Optics 7(10), S265–S269 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: Control of multiphoton transitions is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion while the even terms lead to self-induced transparency. The results hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse width.

    BibTeX: @article{goswamiMultiphotonCoherentControl2005,
     title = {Multiphoton Coherent Control in Complex Systems},
     author = {Goswami, Debabrata},
     date = {2005-09},
     journaltitle = {Journal of Optics B: Quantum and Semiclassical Optics},
     shortjournal = {J. Opt. B: Quantum Semiclass. Opt.},
     volume = {7},
     number = {10},
     pages = {S265--S269},
     issn = {1464-4266},
     doi = {10.1088/1464-4266/7/10/009},
     url = {https://doi.org/10.1088%2F1464-4266%2F7%2F10%2F009},
     urldate = {2019-08-14}
   }
   

3. Quantum Computation with Ultrafast Laser Pulse Shaping. D. Goswami, Resonance 10(6), 8–14 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: Quantum computing exploits the quantum mechanical nature of matter to exist in multiple possible states simultaneously. Building up on the digital binary logic of bits, quantum computing is built on the basis of interacting two-level quantum systems or ‘qubits’ that follow the laws of quantum mechanics. Addressability of the quantum system and its fragility to fidelity are the major issues of concern, which if addressed appropriately, will enable this new approach to revolutionize the present form of computing.

    BibTeX: @article{goswamiQuantumComputationUltrafast2005,
     title = {Quantum Computation with Ultrafast Laser Pulse Shaping},
     author = {Goswami, Debabrata},
     date = {2005-06-01},
     journaltitle = {Resonance},
     shortjournal = {Reson},
     volume = {10},
     number = {6},
     pages = {8--14},
     issn = {0973-712X},
     doi = {10/c3f36s},
     url = {https://doi.org/10.1007/BF02895790},
     urldate = {2019-08-14}
   }
   

4. Heterodimers of Nanoparticles: Formation at a Liquid−Liquid Interface and Particle-Specific Surface Modification by Functional Molecules. H. Gu, Z. Yang, J. Gao, C. K. Chang, and B. Xu, Journal of the American Chemical Society 127(1), 34–35 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: On the basis of a fundamental property of nanoparticles, the self-assembling at a liquid−liquid interface to form “colloidosomes”, a heterogeneous reaction takes place on the exposed surface of the nanoparticles to produce the heterodimers of two distinct nanospheres, which can be modified by two different functional molecules in a particle-specific manner.

    BibTeX: @article{guHeterodimersNanoparticlesFormation2005,
     title = {Heterodimers of {{Nanoparticles}}:\, {{Formation}} at a {{Liquid}}−{{Liquid Interface}} and {{Particle-Specific Surface Modification}} by {{Functional Molecules}}},
     shorttitle = {Heterodimers of {{Nanoparticles}}},
     author = {Gu, Hongwei and Yang, Zhimou and Gao, Jinhao and Chang, C. K. and Xu, Bing},
     date = {2005-01-01},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {127},
     number = {1},
     pages = {34--35},
     issn = {0002-7863},
     doi = {10/dxqtsd},
     url = {https://doi.org/10.1021/ja045220h},
     urldate = {2019-10-01}
   }
   

5. Expanding the Optical Trapping Range of Gold Nanoparticles. P. M. Hansen, V. K. Bhatia, N. Harrit, and L. Oddershede, Nano Letters 5(10), 1937–1942 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate stable three-dimensional (3D) single-beam optical trapping of gold nanoparticles with diameters between 18 and 254 nm. Three-dimensional power spectral analysis reveals that, for nanoparticles with diameters less than 100 nm, the trap stiffness is proportional to the volume of the particle. For larger particles, the trap stiffness still increases with size, however, less steeply. Finally, we provide numbers for the largest forces exertable on gold nanoparticles.

    BibTeX: @article{hansenExpandingOpticalTrapping2005,
     title = {Expanding the {{Optical Trapping Range}} of {{Gold Nanoparticles}}},
     author = {Hansen, Poul Martin and Bhatia, Vikram Kjøller and Harrit, Niels and Oddershede, Lene},
     date = {2005-10-01},
     journaltitle = {Nano Letters},
     shortjournal = {Nano Lett.},
     volume = {5},
     number = {10},
     pages = {1937--1942},
     issn = {1530-6984},
     doi = {10.1021/nl051289r},
     url = {https://doi.org/10.1021/nl051289r},
     urldate = {2019-10-01}
   }
   

6. Novel Optical and Statistical Methods Reveal Colloid–Wall Interactions Inconsistent with DLVO and Lifshitz Theories. P. M. Hansen, J. K. Dreyer, J. Ferkinghoff-Borg, and L. Oddershede, Journal of Colloid and Interface Science 287(2), 561–571 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: We present an experimental method based on video microscopy to perform nanometer scale position detection of a micrometer bead in the direction along the propagation of the detection light. Using the same bead for calibration and detection significantly improves the in depth resolution in comparison to video microscopy methods from literature. This method is used together with an optical trap to measure interaction potentials between a glass surface and colloids made of polystyrene or silica at different electrolyte concentrations. The results are confirmed by an independent method where the optical trap is used in connection with a quadrant photodiode. Also, we present a maximum likelihood analysis method which considerably improves the spatial resolution of interaction potentials by optimizing the underlying potential function to fit all observed position distributions. The measured interaction potentials agree well with DLVO theory for small electrolyte concentrations; however, for larger electrolyte concentrations the potentials differ qualitatively from both DLVO and Lifshitz theory.

    BibTeX: @article{hansenNovelOpticalStatistical2005,
     title = {Novel Optical and Statistical Methods Reveal Colloid–Wall Interactions Inconsistent with {{DLVO}} and {{Lifshitz}} Theories},
     author = {Hansen, Poul Martin and Dreyer, Jakob Kisbye and Ferkinghoff-Borg, Jesper and Oddershede, Lene},
     date = {2005-07-15},
     journaltitle = {Journal of Colloid and Interface Science},
     shortjournal = {Journal of Colloid and Interface Science},
     volume = {287},
     number = {2},
     pages = {561--571},
     issn = {0021-9797},
     doi = {10/dnc43n},
     url = {http://www.sciencedirect.com/science/article/pii/S0021979705001104},
     urldate = {2019-10-01}
   }
   

7. Core-Modified Expanded Porphyrins with Large Third-Order Nonlinear Optical Response. H. Rath, J. Sankar, V. PrabhuRaja, T. K. Chandrashekar, A. Nag, and D. Goswami, Journal of the American Chemical Society 127(33), 11608–11609 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: The third-order nonlinear optical response through measurement of two-photon absorption cross-sections (TPACS) for aromatic core-modified expanded porphyrin analogues by a femtosecond open aperture Z-scan method is reported. The values reported here are among the largest known so far in the literature for any organic molecules.

    BibTeX: @article{rathCoreModifiedExpandedPorphyrins2005,
     title = {Core-{{Modified Expanded Porphyrins}} with {{Large Third-Order Nonlinear Optical Response}}},
     author = {Rath, Harapriya and Sankar, Jeyaraman and PrabhuRaja, Viswanathan and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata},
     date = {2005-08-24},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {127},
     number = {33},
     pages = {11608--11609},
     issn = {0002-7863},
     doi = {10/c2tqsv},
     url = {https://doi.org/10.1021/ja0537575},
     urldate = {2019-08-14}
   }
   

8. Polarization-Induced Modulation of a Femtosecond Nonlinear Process. A. Srivastava and D. Goswami, Physics Letters A 341(5), 523–526 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: We present experimental evidence of laser-induced polarization preference for the highly nonlinear phenomenon of supercontinuum generation. Such results have been arrived through the choice of isotropic and anisotropic materials interacting with femtosecond laser pulses of changing ellipticity. Experimental evidence of additional polarization effects is also present in anisotropic materials. Laser polarization emerges as an important control parameter that exhibits counterintuitive dependence in generating the corresponding high-order nonlinear phenomenon.

    BibTeX: @article{srivastavaPolarizationinducedModulationFemtosecond2005,
     title = {Polarization-Induced Modulation of a Femtosecond Nonlinear Process},
     author = {Srivastava, Alok and Goswami, Debabrata},
     date = {2005-06-27},
     journaltitle = {Physics Letters A},
     shortjournal = {Physics Letters A},
     volume = {341},
     number = {5},
     pages = {523--526},
     issn = {0375-9601},
     doi = {10/crsvpk},
     url = {http://www.sciencedirect.com/science/article/pii/S0375960105006584},
     urldate = {2019-08-14}
   }
   

2004

1. Power Spectrum Analysis for Optical Tweezers. K. Berg-Sørensen and H. Flyvbjerg, Review of Scientific Instruments 75(3), 594–612 (2004) [PDF] [BibTeX]

    BibTeX: @article{berg-sorensenPowerSpectrumAnalysis2004,
     title = {Power Spectrum Analysis for Optical Tweezers},
     author = {Berg-Sørensen, Kirstine and Flyvbjerg, Henrik},
     date = {2004-02-18},
     journaltitle = {Review of Scientific Instruments},
     shortjournal = {Review of Scientific Instruments},
     volume = {75},
     number = {3},
     pages = {594--612},
     issn = {0034-6748},
     doi = {10/cbss66},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.1645654},
     urldate = {2019-10-01}
   }
   

2. Directed Assembly and Rupture Mechanics of Colloidal Aggregates. J. P. Pantina and E. M. Furst, Langmuir 20(10), 3940–3946 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: The macroscopic rheological behavior of colloidal gels arises from the micromechanical properties of the gel backbone, which are governed by nanoscale particle interactions. These colloidal interactions have been commonly understood in terms of the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. Recent work has shown, however, that nonidealities, such as surface roughness and charge nonuniformity, may cause the particle interactions to significantly deviate from DLVO predictions at near-contact separations. Here we present novel techniques for directing the assembly of colloidal aggregates that mimic the gel backbone, based on optical micromanipulation of multiple particles using laser tweezers. This also provides an in situ method for measuring near-contact interactions via single-bond rupture forces. We find that PMMA particles aggregated in the presence of nonorganic salts exhibit interparticle bond strengths more than 10 times greater than those predicted by DLVO theory. However, good agreement is found with DLVO predictions when the anionic surfactant sodium dodecyl sulfate (SDS) is used as the flocculant.

    BibTeX: @article{pantinaDirectedAssemblyRupture2004,
     title = {Directed {{Assembly}} and {{Rupture Mechanics}} of {{Colloidal Aggregates}}},
     author = {Pantina, John P. and Furst, Eric M.},
     date = {2004-05-01},
     journaltitle = {Langmuir},
     shortjournal = {Langmuir},
     volume = {20},
     number = {10},
     pages = {3940--3946},
     issn = {0743-7463},
     doi = {10/btmtnz},
     url = {https://doi.org/10.1021/la0364338},
     urldate = {2019-10-01}
   }
   

3. Equilibrium Cluster Formation in Concentrated Protein Solutions and Colloids. A. Stradner, H. Sedgwick, F. Cardinaux, W. C. K. Poon, S. U. Egelhaaf, and P. Schurtenberger, Nature 432(7016), 492–495 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: Controlling interparticle interactions, aggregation and cluster formation is of central importance in a number of areas, ranging from cluster formation in various disease processes to protein crystallography and the production of photonic crystals. Recent developments in the description of the interaction of colloidal particles with short-range attractive potentials have led to interesting findings including metastable liquid–liquid phase separation and the formation of dynamically arrested states (such as the existence of attractive and repulsive glasses, and transient gels)1,2,3,4,5,6,7. The emerging glass paradigm has been successfully applied to complex soft-matter systems, such as colloid–polymer systems8 and concentrated protein solutions9. However, intriguing problems like the frequent occurrence of cluster phases remain10,11,12,13. Here we report small-angle scattering and confocal microscopy investigations of two model systems: protein solutions and colloid–polymer mixtures. We demonstrate that in both systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters. We discuss the relevance of this finding for nucleation processes during protein crystallization, protein or DNA self-assembly and the previously observed formation of cluster and gel phases in colloidal suspensions12,13,14,15,16,17.

    BibTeX: @article{stradnerEquilibriumClusterFormation2004,
     title = {Equilibrium Cluster Formation in Concentrated Protein Solutions and Colloids},
     author = {Stradner, Anna and Sedgwick, Helen and Cardinaux, Frédéric and Poon, Wilson C. K. and Egelhaaf, Stefan U. and Schurtenberger, Peter},
     date = {2004-11},
     journaltitle = {Nature},
     shortjournal = {Nature},
     volume = {432},
     number = {7016},
     pages = {492--495},
     issn = {1476-4687},
     doi = {10/dgtd9p},
     url = {https://www.nature.com/articles/nature03109},
     urldate = {2019-10-01}
   }
   

4. Anomalous Diffusion in Living Yeast Cells. I. M. Tolić-Nørrelykke, E.-L. Munteanu, G. Thon, L. Oddershede, and K. Berg-Sørensen, Physical Review Letters 93(7), 078102 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: The viscoelastic properties of the cytoplasm of living yeast cells were investigated by studying the motion of lipid granules naturally occurring in the cytoplasm. A large frequency range of observation was obtained by a combination of video-based and laser-based tracking methods. At time scales from 10−4 to 102 s, the granules typically perform subdiffusive motion with characteristics different from previous measurements in living cells. This subdiffusive behavior is thought to be due to the presence of polymer networks and membranous structures in the cytoplasm. Consistent with this hypothesis, we observe that the motion becomes less subdiffusive upon actin disruption.

    BibTeX: @article{tolic-norrelykkeAnomalousDiffusionLiving2004,
     title = {Anomalous {{Diffusion}} in {{Living Yeast Cells}}},
     author = {Tolić-Nørrelykke, Iva Marija and Munteanu, Emilia-Laura and Thon, Genevieve and Oddershede, Lene and Berg-Sørensen, Kirstine},
     date = {2004-08-13},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {93},
     number = {7},
     pages = {078102},
     doi = {10/d7hp3v},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.93.078102},
     urldate = {2019-10-01}
   }
   

5. MatLab Program for Precision Calibration of Optical Tweezers. I. M. Tolić-Nørrelykke, K. Berg-Sørensen, and H. Flyvbjerg, Computer Physics Communications 159(3), 225–240 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: Optical tweezers are used as force transducers in many types of experiments. The force they exert in a given experiment is known only after a calibration. Computer codes that calibrate optical tweezers with high precision and reliability in the (x,y)-plane orthogonal to the laser beam axis were written in MatLab (MathWorks Inc.) and are presented here. The calibration is based on the power spectrum of the Brownian motion of a dielectric bead trapped in the tweezers. Precision is achieved by accounting for a number of factors that affect this power spectrum. First, cross-talk between channels in 2D position measurements is tested for, and eliminated if detected. Then, the Lorentzian power spectrum that results from the Einstein–Ornstein–Uhlenbeck theory, is fitted to the low-frequency part of the experimental spectrum in order to obtain an initial guess for parameters to be fitted. Finally, a more complete theory is fitted, a theory that optionally accounts for the frequency dependence of the hydrodynamic drag force and hydrodynamic interaction with a nearby cover slip, for effects of finite sampling frequency (aliasing), for effects of anti-aliasing filters in the data acquisition electronics, and for unintended “virtual” filtering caused by the position detection system. Each of these effects can be left out or included as the user prefers, with user-defined parameters. Several tests are applied to the experimental data during calibration to ensure that the data comply with the theory used for their interpretation: Independence of x- and y-coordinates, Hooke’s law, exponential distribution of power spectral values, uncorrelated Gaussian scatter of residual values. Results are given with statistical errors and covariance matrix. Program summary Title of program: tweezercalib Catalogue identifier: ADTV Program obtainable from: CPC Program Library, Queen’s University of Belfast, N. Ireland. Program Summary URL: http://cpc.cs.qub.ac.uk/summaries/ADTV Computer for which the program is designed and others on which it has been tested: General computer running MatLab (MathWorks Inc.). Programming language used: MatLab (MathWorks Inc.). Uses “Optimization Toolbox” and “Statistics Toolbox”. Memory required to execute with typical data: Of order 4 times the size of the data file. High speed storage required: None No. of lines in distributed program, including test data, etc.: 133183 No. of bytes in distributed program, including test data, etc.: 1043674 Distribution format: tar gzip file Nature of physical problem: Calibrate optical tweezers with precision by fitting theory to experimental power spectrum of position of bead doing Brownian motion in incompressible fluid, possibly near microscope cover slip, while trapped in optical tweezers. Thereby determine spring constant of optical trap and conversion factor for arbitrary-units-to-nanometers for detection system. Method of solution: Elimination of cross-talk between quadrant photo-diode’s output channels for positions (optional). Check that distribution of recorded positions agrees with Boltzmann distribution of bead in harmonic trap. Data compression and noise reduction by blocking method applied to power spectrum. Full accounting for hydrodynamic effects: Frequency-dependent drag force and interaction with nearby cover slip (optional). Full accounting for electronic filters (optional), for “virtual filtering” caused by detection system (optional). Full accounting for aliasing caused by finite sampling rate (optional). Standard non-linear least-squares fitting. Statistical support for fit is given, with several plots suitable for inspection of consistency and quality of data and fit. Restrictions on the complexity of the problem: Data should be positions of bead doing Brownian motion while held by optical tweezers. For high precision in final results, data should be time series measured over a long time, with sufficiently high experimental sampling rate: The sampling rate should be well above the characteristic frequency of the trap, the so-called corner frequency. Thus, the sampling frequency should typically be larger than 10 kHz. The Fast Fourier Transform applied requires the time series to contain 2n data points, and long measurement time is obtained with n>12–15. Finally, the optics should be set to ensure a harmonic trapping potential in the range of positions visited by the bead. The fitting procedure checks for harmonic potential. Typical running time: (Tens of) minutes Unusual features of the program: None References: The theoretical underpinnings for the procedure are found in [K. Berg-Sørensen, H. Flyvbjerg, Rev. Sci. Instrum. 75 (3) (2004) 594].

    BibTeX: @article{tolic-norrelykkeMatLabProgramPrecision2004,
     title = {{{MatLab}} Program for Precision Calibration of Optical Tweezers},
     author = {Tolić-Nørrelykke, Iva Marija and Berg-Sørensen, Kirstine and Flyvbjerg, Henrik},
     date = {2004-06-01},
     journaltitle = {Computer Physics Communications},
     shortjournal = {Computer Physics Communications},
     volume = {159},
     number = {3},
     pages = {225--240},
     issn = {0010-4655},
     doi = {10/fgkfzg},
     url = {http://www.sciencedirect.com/science/article/pii/S0010465504001043},
     urldate = {2019-10-01}
   }
   

2003

1. Gelation in Model Colloid−Polymer Mixtures. J. Bergenholtz, W. C. K. Poon, and M. Fuchs, Langmuir 19(10), 4493–4503 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Mode coupling theory (MCT) is used to model gel formation in mixtures of colloidal particles and nonadsorbing polymer. The polymer induces an effective, short-range attraction among the colloids, which is modeled by a depletion attraction of the Asakura−Oosawa form. This enables the MCT to be solved analytically for dilute systems, leading to a prediction, free of adjustable parameters, of the location of the gel boundary in the phase diagram. For concentrated systems, a simple mapping is suggested that makes a previous theory for Yukawa interactions applicable to colloid−polymer mixtures. The results are compared against Monte Carlo simulations and experiments on model systems. Excellent agreement is observed at high colloid concentrations, where the theory predicts melting of glassy structures on addition of small amounts of polymer. Further addition of polymer causes gelation, in semiquantitative accord with experimental data at moderate to high colloid concentrations. However, at lower concentrations the theory is unable to capture the onset of transient gelation.

    BibTeX: @article{bergenholtzGelationModelColloid2003,
     title = {Gelation in {{Model Colloid}}−{{Polymer Mixtures}}},
     author = {Bergenholtz, J. and Poon, W. C. K. and Fuchs, M.},
     date = {2003-05-01},
     journaltitle = {Langmuir},
     shortjournal = {Langmuir},
     volume = {19},
     number = {10},
     pages = {4493--4503},
     issn = {0743-7463},
     doi = {10/bdsbxs},
     url = {https://doi.org/10.1021/la0340089},
     urldate = {2019-10-01}
   }
   

2. Optical Computing. D. Goswami, Resonance 8(6), 56–71 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Optics has been used in computing for a number of years but the main emphasis has been and continues to be to link portions of computers, for communications, or more intrinsically in devices that have some optical application or component (optical pattern recognition, etc). Optical digital computers are still some years away, however a number of devices that can ultimately lead to real optical computers have already been manufactured, including optical logic gates, optical switches, optical interconnections, and optical memory. The most likely near-term optical computer will really be a hybrid composed of traditional architectural design along with some portions that can perform some functional operations in optical mode.

    BibTeX: @article{goswamiOpticalComputing2003,
     title = {Optical Computing},
     author = {Goswami, Debabrata},
     date = {2003-06-01},
     journaltitle = {Resonance},
     shortjournal = {Reson},
     volume = {8},
     number = {6},
     pages = {56--71},
     issn = {0973-712X},
     doi = {10/d5qtw5},
     url = {https://doi.org/10.1007/BF02837869},
     urldate = {2019-08-14}
   }
   

3. Optical Pulse Shaping Approaches to Coherent Control. D. Goswami, Physics Reports 374(6), 385–481 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: The last part of the twentieth century has experienced a huge resurge of activity in the field of coherent light–matter interaction, more so in attempting to exert control over such interactions. Birth of coherent control was originally spurred by the theoretical understanding of the quantum interferences that lead to energy randomization and experimental developments in ultrafast laser spectroscopy. The theoretical predictions on control of reaction channels or energy randomization processes are still more dramatic than the experimental demonstrations, though this gap between the two is consistently reducing over the recent years with realistic theoretical models and technological developments. Experimental demonstrations of arbitrary optical pulse shaping have made some of the previously impracticable theoretical predictions possible to implement. Starting with the simple laser modulation schemes to provide proof-of-the-principle demonstrations, feedback loop pulse shaping systems have been developed that can actively manipulate some atomic and molecular processes. This tremendous experimental boost of optical pulse shaping developments has prospects and implications into many more new directions, such as quantum computing and terabit/sec data communications. This review captures certain aspects and impacts of optical pulse shaping into the fast developing areas of coherent control and other related fields. Currently available reviews focus on one or the other detailed aspects of coherent control, and the reader will be referred to such details as and when necessary for issues that are dealt in brief here. We will focus on the current issues including control of intramolecular dynamics and make connections to the future concepts, such as, quantum computation, biomedical applications, etc.

    BibTeX: @article{goswamiOpticalPulseShaping2003,
     title = {Optical Pulse Shaping Approaches to Coherent Control},
     author = {Goswami, Debabrata},
     date = {2003-02-01},
     journaltitle = {Physics Reports},
     shortjournal = {Physics Reports},
     volume = {374},
     number = {6},
     pages = {385--481},
     issn = {0370-1573},
     doi = {10/fwwrc5},
     url = {http://www.sciencedirect.com/science/article/pii/S0370157302004805},
     urldate = {2019-08-14}
   }
   

4. Control of Supercontinuum Generation with Polarization of Incident Laser Pulses. A. Srivastava and D. Goswami, Applied Physics B 77(2), 325–328 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Supercontinuum generation is dependent on the polarization state of the incident laser. The polarization of the generated supercontinuum is the same as that of the incident laser. The magnitude of the generated supercontinuum depends on the polarization of the incident laser and increases as the polarization changes from circular to linear, irrespective of the nature of the sample, be it isotropic, anisotropic, or chiral. In all samples, the polarization dependence indicates a preference for the linear component of the incident laser beam. The anisotropic sample shows an additional difference in the generated supercontinuum for the two perpendicular directions of the incident laser polarization.

    BibTeX: @article{srivastavaControlSupercontinuumGeneration2003,
     title = {Control of Supercontinuum Generation with Polarization of Incident Laser Pulses},
     author = {Srivastava, A. and Goswami, D.},
     date = {2003-09-01},
     journaltitle = {Applied Physics B},
     shortjournal = {Appl Phys B},
     volume = {77},
     number = {2},
     pages = {325--328},
     issn = {1432-0649},
     doi = {10/bhqfj6},
     url = {https://doi.org/10.1007/s00340-003-1243-2},
     urldate = {2019-08-14}
   }
   

2002

1. Decoherence Control in Quantum Computing with Simple Chirped Pulses. D. Goswami, Pramana 59(2), 235–242 (2002) [Abstract] [PDF] [BibTeX]

   Abstract: We show how the use of optimally shaped pulses to guide the time evolution of a system (‘coherent control’) can be an effective approach towards quantum computation logic. We demonstrate this with selective control of decoherence for a multilevel system with a simple linearly chirped pulse. We use a multiphoton density-matrix approach to explore the effects of ultrafast shaped pulses for two-level systems that do not have a single photon resonance, and show that many multiphoton results are surprisingly similar to the single-photon results. Finally, we choose two specific chirped pulses: one that always generates inversion and the other that always generates self-induced transparency to demonstrate an ensemble CNOT gate.

    BibTeX: @article{goswamiDecoherenceControlQuantum2002,
     title = {Decoherence Control in Quantum Computing with Simple Chirped Pulses},
     author = {Goswami, Debabrata},
     date = {2002-08-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {59},
     number = {2},
     pages = {235--242},
     issn = {0973-7111},
     doi = {10/bv363m},
     url = {https://doi.org/10.1007/s12043-002-0113-5},
     urldate = {2019-08-14}
   }
   

2. Erratum: Laser Phase Modulation Approaches towards Ensemble Quantum Computing [Phys. Rev. Lett.0031–9007PRLTAO \textbf88 , 177901 (2002)]. D. Goswami, Physical Review Letters 89(27), 279901 (2002) [PDF] [BibTeX]

    BibTeX: @article{goswamiErratumLaserPhase2002,
     title = {Erratum: {{Laser Phase Modulation Approaches}} towards {{Ensemble Quantum Computing}} [{{Phys}}. {{Rev}}. {{Lett}}.0031–{{9007PRLTAO}} {\textbf{88}} , 177901 (2002)]},
     shorttitle = {Erratum},
     author = {Goswami, Debabrata},
     date = {2002-12-18},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {89},
     number = {27},
     pages = {279901},
     issn = {0031-9007, 1079-7114},
     doi = {10/chtkbd},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.89.279901},
     urldate = {2019-08-14}
   }
   

3. Laser Phase Modulation Approaches towards Ensemble Quantum Computing. D. Goswami, Physical Review Letters 88(17), 177901 (2002) [Abstract] [PDF] [BibTeX]

   Abstract: Selective control of decoherence is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion, while the even terms lead to self-induced transparency. These results also hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse width. Such results form the basis of a robustly implementable CNOT gate.

    BibTeX: @article{goswamiLaserPhaseModulation2002,
     title = {Laser {{Phase Modulation Approaches}} towards {{Ensemble Quantum Computing}}},
     author = {Goswami, Debabrata},
     date = {2002-04-15},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {88},
     number = {17},
     pages = {177901},
     doi = {10/c339br},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.88.177901},
     urldate = {2019-08-14}
   }
   

4. Prospects of Ultrafast Pulse Shaping. A. Sharan and D. Goswami, Current Science 82(1), 30–37 (2002) [Abstract] [PDF] [BibTeX]

   Abstract: Availability of femtosecond solid-state lasers around the world has spurred a lot of technological activity in the femtosecond timescale and has also given us a tool to probe and gain more insight into the fundamentals of physics, chemistry and biology. An eventual prospect of controlling and manipulating some of the hitherto impossible tasks, can perhaps now be dreamt of. In this review we give a brief account of some of the promising techniques for ultrafast laser pulse shaping and then list some of the exciting prospects.

    BibTeX: @article{sharanProspectsUltrafastPulse2002,
     title = {Prospects of Ultrafast Pulse Shaping},
     author = {Sharan, Alok and Goswami, Debabrata},
     date = {2002},
     journaltitle = {Current Science},
     volume = {82},
     number = {1},
     eprint = {24105924},
     eprinttype = {jstor},
     pages = {30--37},
     issn = {0011-3891},
     url = {https://www.jstor.org/stable/24105924},
     urldate = {2019-08-14}
   }
   

2001

1. Fast-Frequency-Hopping Modulation and Detection Demonstration. M. R. Fetterman, J. C. Davis, H.-S. Tan, W. Yang, D. Goswami, J.-K. Rhee, and W. S. Warren, JOSA B 18(9), 1372–1376 (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate fast-frequency-hopping modulation that exploits the unique features of acousto-optic-modulator based laser pulse shaping and the spectrally and temporally resolved upconversion technique (STRUT) pulse-characterization method. These pulses have been specifically designed so that they can be characterized by the STRUT, without any processing of the STRUT data set. We present examples of complex fast-frequency-hopping laser pulses that have been generated and characterized by our pulse-shaping system and STRUT. We discuss the theoretical limitations on the data rate that can be obtained with such a technique.

    BibTeX: @article{fettermanFastfrequencyhoppingModulationDetection2001,
     title = {Fast-Frequency-Hopping Modulation and Detection Demonstration},
     author = {Fetterman, M. R. and Davis, J. C. and Tan, H.-S. and Yang, W. and Goswami, D. and Rhee, J.-K. and Warren, W. S.},
     date = {2001-09-01},
     journaltitle = {JOSA B},
     shortjournal = {J. Opt. Soc. Am. B, JOSAB},
     volume = {18},
     number = {9},
     pages = {1372--1376},
     issn = {1520-8540},
     doi = {10/bqpmmt},
     url = {https://www.osapublishing.org/josab/abstract.cfm?uri=josab-18-9-1372},
     urldate = {2019-08-14}
   }
   

2. Coherent Control of Multiphoton Transitions with Femtosecond Pulse Shaping. S. A. Hosseini and D. Goswami, Physical Review A 64(3), 033410 (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We explore the effects of ultrafast shaped pulses for two-level systems that do not have a single-photon resonance, by developing a multiphoton density-matrix approach. We take advantage of the fact that the dynamics of the intermediate virtual states are absent within our laser pulse time scales. Under these conditions, the multiphoton results are similar to those for a single photon, and it is possible to extend the single-photon coherent control ideas to develop multiphoton coherent control.

    BibTeX: @article{hosseiniCoherentControlMultiphoton2001,
     title = {Coherent Control of Multiphoton Transitions with Femtosecond Pulse Shaping},
     author = {Hosseini, S. Abbas and Goswami, Debabrata},
     date = {2001-08-09},
     journaltitle = {Physical Review A},
     shortjournal = {Phys. Rev. A},
     volume = {64},
     number = {3},
     pages = {033410},
     doi = {10/ffjx3v},
     url = {https://link.aps.org/doi/10.1103/PhysRevA.64.033410},
     urldate = {2019-08-14}
   }
   

3. High-Ratio Electro-optical Data Compression for Massive Accessing Networks Using AOM-based Ultrafast Pulse Shaping. W. Yang, M. R. Fetterman, D. Goswami, and W. S. Warren, Journal of Optical Communications 22(1), 15–18 (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate the compression of a 3.5 Mbit/s electronic data packet into an optical data packet with 700-Gbit/s effective data rate. The compressed optical data packet can be subsequently decompressed in the optical domain using lump dispersion devices. Combined with high speed optical add-drops [1-5], this high ratio data compression technique enables thousands of electronic end-users to share the bandwidthabundant optical channel directly and simultaneously.

    BibTeX: @article{yangHighratioElectroopticalData2001,
     title = {High-Ratio {{Electro-optical Data Compression}} for {{Massive Accessing Networks Using AOM-based Ultrafast Pulse Shaping}}},
     author = {Yang, Weiguo and Fetterman, Matthew R. and Goswami, Debabrata and Warren, Warren S.},
     date = {2001},
     journaltitle = {Journal of Optical Communications},
     volume = {22},
     number = {1},
     pages = {15--18},
     issn = {2191-6322},
     doi = {10/gf6c93},
     url = {https://www.degruyter.com/dg/viewarticle/j$002fjoc.2001.22.1$002fjoc.2001.22.1.15$002fjoc.2001.22.1.15.xml},
     urldate = {2019-08-14}
   }
   

2000

1. Driving Wave Packet Recurrences with Optimally Modulated Laser Pulses. B. M. Goodson, D. Goswami, H. Rabitz, and W. S. Warren, The Journal of Chemical Physics 112(11), 5081–5090 (2000) [Abstract] [PDF] [BibTeX]

   Abstract: In the weak-field limit, laser pulses optimized to induce vibrational wave packet recurrences in excited state potentials were calculated for Morse oscillators and for a real system [the X\mkern1mu1Σ+ and A\mkern1mu3Π(1) states of IBr]. The performance of the optimized pulses was studied via simulated wave packet propagation. Such optimal light fields may be computationally generated given only the form of the electronic potential surfaces, knowledge of the particular ground state supplying population, and simple molecular constants. Thus it should be possible to use the modulation of light fields experimentally optimized to achieve recurrences in order to obtain substantial information regarding previously uncharacterized potential surfaces in both diatomic and polyatomic molecules. Moreover, it should be possible to generalize this approach to the strong-field limit.

    BibTeX: @article{goodsonDrivingWavePacket2000,
     title = {Driving Wave Packet Recurrences with Optimally Modulated Laser Pulses},
     author = {Goodson, Boyd M. and Goswami, Debabrata and Rabitz, Herschel and Warren, Warren S.},
     date = {2000-03-03},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {112},
     number = {11},
     pages = {5081--5090},
     issn = {0021-9606},
     doi = {10/cgpwmf},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.481062},
     urldate = {2019-08-14}
   }
   

2. Suppression of Supercontinuum Generation with Circularly Polarized Light. A. S. Sandhu, S. Banerjee, and D. Goswami, Optics Communications 181(1), 101–107 (2000) [Abstract] [PDF] [BibTeX]

   Abstract: Controlling a nonlinear process such as supercontinuum generation (SG) with the polarization-state of laser is an important demonstration of laser selectivity. We show that the threshold for SG and the total amount of supercontinuum generated depends on incident laser polarization for isotropic samples. Irrespective of the nature of the samples chosen, SG efficiency decreases as the incident laser polarization changes from linear to circular and thus, provides the first experimental demonstration of the suppression of SG with circularly polarized light. The ratio of the overall SG between the linear and circular polarization (i.e., measure of suppression) undergoes an intensity dependent decrease from large initial values to asymptotic limits, irrespective of samples.

    BibTeX: @article{sandhuSuppressionSupercontinuumGeneration2000,
     title = {Suppression of Supercontinuum Generation with Circularly Polarized Light},
     author = {Sandhu, Arvinder S and Banerjee, Sudeep and Goswami, Debabrata},
     date = {2000-07-01},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {181},
     number = {1},
     pages = {101--107},
     issn = {0030-4018},
     doi = {10/brwfhq},
     url = {http://www.sciencedirect.com/science/article/pii/S0030401800007525},
     urldate = {2019-08-14}
   }
   

1999

1. Propagation of Complex Laser Pulses in Optically Dense Media. M. R. Fetterman, J. C. Davis, D. Goswami, W. Yang, and W. S. Warren, Physical Review Letters 82(20), 3984–3987 (1999) [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast laser pulses with complex envelopes (amplitude and frequency modulated) are used to excite an optically dense column of rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation in the Rb vapor are all shown to depend strongly on the laser pulse shape. Pulses that produce adiabatic passage in the optically thin limit exhibit more complex behavior in optically thick samples, including an unexpected dependence on the sign of the frequency sweep. Numerical solutions of the Maxwell-Bloch equations are shown to account for our results.

    BibTeX: @article{fettermanPropagationComplexLaser1999,
     title = {Propagation of {{Complex Laser Pulses}} in {{Optically Dense Media}}},
     author = {Fetterman, M. R. and Davis, J. C. and Goswami, D. and Yang, W. and Warren, W. S.},
     date = {1999-05-17},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {82},
     number = {20},
     pages = {3984--3987},
     doi = {10/dgk8pv},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.82.3984},
     urldate = {2019-08-14}
   }
   

2. Real-Time Adaptive Amplitude Feedback in an AOM-based Ultrafast Optical Pulse Shaping System. Weiguo Yang, Feng Huang, M. R. Fetterman, J. C. Davis, D. Goswami, and W. S. Warren, IEEE Photonics Technology Letters 11(12), 1665–1667 (1999) [Abstract] [BibTeX]

   Abstract: We demonstrate real-time adaptive amplitude feedback in an AOM-based ultrafast optical pulse shaping system operating at /spl lambda/=1550 nm wavelength for optical communication applications. At the optimized feedback depth, a simple negative feedback algorithm converges in fewer than 10 iterations to within 5% of the target shape. This technique may be very useful for many applications including spectrum-sliced WDM.

    BibTeX: @article{weiguoyangRealtimeAdaptiveAmplitude1999,
     title = {Real-Time Adaptive Amplitude Feedback in an {{AOM-based}} Ultrafast Optical Pulse Shaping System},
     author = {{Weiguo Yang} and {Feng Huang} and Fetterman, M. R. and Davis, J. C. and Goswami, D. and Warren, W. S.},
     date = {1999-12},
     journaltitle = {IEEE Photonics Technology Letters},
     volume = {11},
     number = {12},
     pages = {1665--1667},
     issn = {1041-1135},
     doi = {10/dvrf7c}
   }
   

1998

1. Ultrafast Pulse Shaping: Amplification and Characterization. M. R. Fetterman, D. Goswami, D. Keusters, W. Yang, J.-K. Rhee, and W. S. Warren, Optics Express 3(10), 366–375 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate high-resolution amplified pulse shaping using an acousto-optic modulator (AOM) at a center-wavelength of 795nm. The output pulses have energy of 200μJ/pulse and a transform-limited pulsewidth of 150fs. A spectral modulation of over 40 features is achieved in a single pulse. We characterize the pulses using the STRUT (Spectrally and Temporally Resolved Upconversion Technique). Using predistortion techniques, we demonstrate that the pulses can be shaped in amplitude and phase. We create a complex pulse shape with hyperbolic secant amplitude and hyperbolic tangent frequency sweep, which is useful for applications in adiabatic rapid passage experiments.

    BibTeX: @article{fettermanUltrafastPulseShaping1998,
     title = {Ultrafast Pulse Shaping: Amplification and Characterization},
     shorttitle = {Ultrafast Pulse Shaping},
     author = {Fetterman, M. R. and Goswami, D. and Keusters, D. and Yang, W. and Rhee, J.-K. and Warren, W. S.},
     date = {1998-11-09},
     journaltitle = {Optics Express},
     shortjournal = {Opt. Express, OE},
     volume = {3},
     number = {10},
     pages = {366--375},
     issn = {1094-4087},
     doi = {10/czfxs8},
     url = {https://www.osapublishing.org/oe/abstract.cfm?uri=oe-3-10-366},
     urldate = {2019-08-14}
   }
   

2. Interference Model for Back-Focal-Plane Displacement Detection in Optical Tweezers. F. Gittes and C. F. Schmidt, Optics Letters 23(1), 7–9 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: The lateral position of an optically trapped object in a microscope can be monitored with a quadrant photodiode to within nanometers or better by measurement of intensity shifts in the back focal plane of the lens that is collimating the outgoing laser light. This detection is largely independent of the position of the trap in the field of view. We provide a model for the essential mechanism of this type of detection, giving a simple, closed-form analytic solution with simplifying assumptions. We identify intensity shifts as first-order far-field interference between the outgoing laser beam and scattered light from the trapped particle, where the latter is phase advanced owing to the Gouy phase anomaly. This interference also reflects momentum transfer to the particle, giving the spring constant of the trap. Our response formula is compared with the results of experiments.

    BibTeX: @article{gittesInterferenceModelBackfocalplane1998,
     title = {Interference Model for Back-Focal-Plane Displacement Detection in Optical Tweezers},
     author = {Gittes, Frederick and Schmidt, Christoph F.},
     date = {1998-01-01},
     journaltitle = {Optics Letters},
     shortjournal = {Opt. Lett., OL},
     volume = {23},
     number = {1},
     pages = {7--9},
     issn = {1539-4794},
     doi = {10/bjwpvd},
     url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-23-1-7},
     urldate = {2019-10-01}
   }
   

3. Laser Enhanced NMR Spectroscopy, Revisited. W. S. Warren, D. Goswami, and S. Mayr, Molecular Physics 93(3), 371–375 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: Experimental investigations of the effects of moderately powerful (10–20 W cm-2) offresonant continuous lasers on NMR spectra provide no evidence for the B (3) field recently proposed, or for any other mechanism which depends on the light polarization. Observed 1H and 13C line shifts with argon-ion laser irradiation for the molecule p -methoxyphenyliminocamphor mostly can be explained by heating effects. Residual shifts due to other mechanisms appear to be at most 0·1 Hz (5% of the linewidth). One mechanism which could account for residual shifts of this magnitude is differences between NMR frequencies in the excited (triplet) and ground electronic states, although our data have insufficient resolution to make definitive claims. However, it seems unlikely that this effect can be made sufficiently large to give practical resolution enhancements without massive heating.

    BibTeX: @article{warrenLaserEnhancedNMR1998,
     title = {Laser Enhanced {{NMR}} Spectroscopy, Revisited},
     author = {Warren, W. S. and Goswami, Debabrata and Mayr, Suzanne},
     date = {1998-02-01},
     journaltitle = {Molecular Physics},
     volume = {93},
     number = {3},
     pages = {371--375},
     issn = {0026-8976},
     doi = {10/c692sm},
     url = {https://doi.org/10.1080/002689798169041},
     urldate = {2019-08-14}
   }
   

4. Rapid Ultrafine-Tunable Optical Delay Line at the 1.55-Μm Wavelength. W. Yang, D. Keusters, D. Goswami, and W. S. Warren, Optics Letters 23(23), 1843–1845 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: A fast, ultrafine-tunable delay line at 1550 nm is demonstrated by use of acousto-optic pulse shaping. Delays of up to 30 ps can be achieved without any optical readjustment. The delay is linear to the rf center frequency applied to the acousto-optic modulator and is fully electronic. It takes only 3 µs to switch between different time slots, irrespective of the time separation in the tuning range of 30 ps; for a smaller tuning range the tuning speed can be faster. The tuning resolution and range depend on the choice of system parameters. The pulse energy can be regulated by rf power.

    BibTeX: @article{yangRapidUltrafinetunableOptical1998,
     title = {Rapid Ultrafine-Tunable Optical Delay Line at the 1.55-Μm Wavelength},
     author = {Yang, Weiguo and Keusters, Dorine and Goswami, Debabrata and Warren, Warren S.},
     date = {1998-12-01},
     journaltitle = {Optics Letters},
     shortjournal = {Opt. Lett., OL},
     volume = {23},
     number = {23},
     pages = {1843--1845},
     issn = {1539-4794},
     doi = {10/fq4dfs},
     url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-23-23-1843},
     urldate = {2019-08-14}
   }
   

1994

1. Effects of Pulses with Simple Phase and Frequency Modulations. D. Goswami and W. S. Warren, Physical Review A 50(6), 5190–5196 (1994) [Abstract] [PDF] [BibTeX]

   Abstract: The effects of pulse shapes with simple phase and frequency modulation (phase proportional to amplitude or intensity, frequency proportional to intensity) are explored numerically. Many such shapes can be generated by combining self-phase-modulation with modern laser pulse-shaping capabilities (which are more flexible for amplitude modulation than for frequency modulation). Even though all of these wave forms begin and end at the same frequency (and hence violate the mathematical conditions for adiabatic inversion), we show that they can generate adiabatic population inversion or suppress intramolecular energy redistribution.

    BibTeX: @article{goswamiEffectsPulsesSimple1994,
     title = {Effects of Pulses with Simple Phase and Frequency Modulations},
     author = {Goswami, Debabrata and Warren, Warren S.},
     date = {1994-12-01},
     journaltitle = {Physical Review A},
     shortjournal = {Phys. Rev. A},
     volume = {50},
     number = {6},
     pages = {5190--5196},
     doi = {10/bnhs43},
     url = {https://link.aps.org/doi/10.1103/PhysRevA.50.5190},
     urldate = {2019-08-14}
   }
   

2. Femtosecond Laser Pulse Shaping by Use of Microsecond Radio-Frequency Pulses. C. W. Hillegas, J. X. Tull, D. Goswami, D. Strickland, and W. S. Warren, Optics Letters 19(10), 737–739 (1994) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate a new pulse-shaping technique, using an acousto-optic modulator as a spatial modulator in a zero-dispersion delay line. Compared with existing techniques, this approach simplifies optical alignment and dramatically improves update rates. It should also improve flexibility for generating complex waveforms.

    BibTeX: @article{hillegasFemtosecondLaserPulse1994,
     title = {Femtosecond Laser Pulse Shaping by Use of Microsecond Radio-Frequency Pulses},
     author = {Hillegas, C. W. and Tull, J. X. and Goswami, D. and Strickland, D. and Warren, W. S.},
     date = {1994-05-15},
     journaltitle = {Optics Letters},
     shortjournal = {Opt. Lett., OL},
     volume = {19},
     number = {10},
     pages = {737--739},
     issn = {1539-4794},
     doi = {10/bgs6mn},
     url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-19-10-737},
     urldate = {2019-08-14}
   }
   

3. Adiabatic Population Transfer with Frequency‐swept Laser Pulses. J. S. Melinger, S. R. Gandhi, A. Hariharan, D. Goswami, and W. S. Warren, The Journal of Chemical Physics 101(8), 6439–6454 (1994) [Abstract] [PDF] [BibTeX]

   Abstract: We present detailed experimental and theoretical results on population transfer with frequency‐swept picosecond laser pulses. Here, we demonstrate that intense frequency‐swept pulses, when applied in the adiabatic limit, lead to both more efficient and more selective excitation than do unmodulated laser pulses. The experimental work is performed on quasi‐two‐level systems (pentacene/p‐terphenyl crystal and Na vapor), quasi‐three‐level systems (Na vapor), and on more complex multilevel systems (I2 vapor). We discuss the different characteristics of adiabatic population transfer in both few‐level, and multilevel cases, and, in particular, present computer calculations to explore the effects of molecular rotations in multilevel adiabatic population transfer.

    BibTeX: @article{melingerAdiabaticPopulationTransfer1994,
     title = {Adiabatic Population Transfer with Frequency‐swept Laser Pulses},
     author = {Melinger, J. S. and Gandhi, Suketu R. and Hariharan, A. and Goswami, D. and Warren, W. S.},
     date = {1994-10-15},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {101},
     number = {8},
     pages = {6439--6454},
     issn = {0021-9606},
     doi = {10/dbhhsg},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.468368},
     urldate = {2019-08-14}
   }
   

1993

1. Control of Chemical Dynamics by Restricting Intramolecular Vibrational Relaxation. D. Goswami and W. S. Warren, The Journal of Chemical Physics 99(6), 4509–4517 (1993) [Abstract] [PDF] [BibTeX]

   Abstract: We address the issue of localization of bond energy in a molecule by stopping intramolecular vibrational relaxation (IVR). We show through model calculations that appropriate frequency sweeps permit selective locking over a well‐defined range of resonance frequencies, with little excitation outside that range. We also propose a modified version of an adiabatic half passage experiment that will perform photon locking without complications from inhomogeneities or partial excitation of other transitions for a bright state coupled to a finite number of dark states.

    BibTeX: @article{goswamiControlChemicalDynamics1993,
     title = {Control of Chemical Dynamics by Restricting Intramolecular Vibrational Relaxation},
     author = {Goswami, Debabrata and Warren, Warren S.},
     date = {1993-09-15},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {99},
     number = {6},
     pages = {4509--4517},
     issn = {0021-9606},
     doi = {10/bjh64b},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.466050},
     urldate = {2019-08-14}
   }
   

1992

1. Laser-Enhanced NMR Spectroscopy. W. S. Warren, S. Mayr, D. Goswami, and A. P. West, Science 255(5052), 1683–1685 (1992) [Abstract] [PDF] [BibTeX]

   Abstract: Experimental studies show that optical irradiation far from any absorption bands can shift the resonances in a nuclear magnetic resonance (NMR) spectrum without significant heating. This effect may lead to increased dispersion in NMR studies of complex molecules.

    BibTeX: @article{warrenLaserenhancedNMRSpectroscopy1992,
     title = {Laser-Enhanced {{NMR}} Spectroscopy},
     author = {Warren, W. S. and Mayr, S. and Goswami, D. and West, A. P.},
     date = {1992-03-27},
     journaltitle = {Science},
     volume = {255},
     number = {5052},
     eprint = {1553555},
     eprinttype = {pmid},
     pages = {1683--1685},
     issn = {0036-8075, 1095-9203},
     doi = {10/fr8pjn},
     url = {https://science.sciencemag.org/content/255/5052/1683},
     urldate = {2019-08-14}
   }
   

1991

1. Fluorescence Quenching of Few Aromatic Amines by Chlorinated Methanes. D. Goswami, R. S. Sarpal, and S. K. Dogra, Bulletin of the Chemical Society of Japan 64(10), 3137–3141 (1991) [Abstract] [PDF] [BibTeX]

   Abstract: Fluorescence quenching of few aromatic amines; aniline (AB), 1-naphthylamine (1-AN), 2-naphthylamine (2-AN), 2,3-naphthalenediamine (2,3-DAN), 9-phenanthrenamine (9-AP), 1-pyrenamine (1-APy), 2-chrysenamine (2-AC), 6-chrysenamine (6-AC), and 3-fluoranthenamine (3-AF) by dichloromethane, chloroform, and carbon tetrachloride has been studied in cyclohexane and acetonitrile. The quenching rate constants (kq) have been determined in both the solvents and these values are nearly independent of the solvent polarity. The values of kq are nearly equal to diffusion-controlled limits (kdiff) for CHCl3 and CCl4 in both the solvents, whereas for CH2Cl2 it is three to four order of magnitude less than kdiff. For a given amine, kq increases with the increase in electron affinity of the quencher, whereas for a given quencher (dichloromethane) kq increases with the increase in singlet state energy of fluorophore. The results obtained are explained in terms of a quenching mechanism involving an intermediate donor–acceptor (DA)* complex formed between the excited aromatic amine and quencher.

    BibTeX: @article{goswamiFluorescenceQuenchingFew1991,
     title = {Fluorescence {{Quenching}} of {{Few Aromatic Amines}} by {{Chlorinated Methanes}}},
     author = {Goswami, Debabrata and Sarpal, Ranjit S. and Dogra, Sneh K.},
     date = {1991-10-01},
     journaltitle = {Bulletin of the Chemical Society of Japan},
     shortjournal = {BCSJ},
     volume = {64},
     number = {10},
     pages = {3137--3141},
     issn = {0009-2673},
     doi = {10/cd4jj6},
     url = {https://www.journal.csj.jp/doi/abs/10.1246/bcsj.64.3137},
     urldate = {2019-08-14}
   }
   

Conference Proceedings

2029-2020

1. Diluting Convective Effects in Femtosecond Laser Induced Thermal Lens Measurements with Thermally Active Constituents. S. Chakraborty, A. K. Mishra, A. K. Rawat, and D. Goswami, in Frontiers in Optics + Laser Science 2022 (FIO, LS) (2022), Paper JW5A.25 (Optica Publishing Group, 2022), p. JW5A.25 [Abstract] [PDF] [BibTeX]

   Abstract: We report Thermal Lens measurements on the binary liquid mixtures of Methanol and Phenol with femtosecond pulse excitations. The photothermal response is found to be strongly dependent on relative concentrations and the constituents’ molecular properties.

    BibTeX: @inproceedings{chakrabortyDilutingConvectiveEffects2022,
     title = {Diluting {{Convective Effects}} in {{Femtosecond Laser Induced Thermal Lens Measurements}} with {{Thermally Active Constituents}}},
     booktitle = {Frontiers in {{Optics}} + {{Laser Science}} 2022 ({{FIO}}, {{LS}}) (2022), Paper {{JW5A}}.25},
     author = {Chakraborty, Subhajit and Mishra, Amit Kumar and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2022-10-17},
     pages = {JW5A.25},
     publisher = {{Optica Publishing Group}},
     url = {https://opg.optica.org/abstract.cfm?uri=FiO-2022-JW5A.25},
     urldate = {2022-12-31},
     eventtitle = {Frontiers in {{Optics}}}
   }
   

2. Understanding the Photothermal Response of CBNP Nanofluids Using Thermal Lens Spectroscopic Techniques. S. Chakraborty, A. K. Mishra, A. K. Rawat, and D. Goswami, in Frontiers in Optics + Laser Science 2021 (2021), Paper JTu1A.99 (Optica Publishing Group, 2021), p. JTu1A.99 [Abstract] [PDF] [BibTeX]

   Abstract: We performed a dual beam Z-Scan experiment to examine the thermal lensing effects in CBNP nanofluids. The photothermal characteristics and heat dissipation dynamics were observed for these nanofluids at different levels of their linear absorption.

    BibTeX: @inproceedings{chakrabortyUnderstandingPhotothermalResponse2021,
     title = {Understanding the {{Photothermal Response}} of {{CBNP Nanofluids Using Thermal Lens Spectroscopic Techniques}}},
     booktitle = {Frontiers in {{Optics}} + {{Laser Science}} 2021 (2021), Paper {{JTu1A}}.99},
     author = {Chakraborty, Subhajit and Mishra, Amit Kumar and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2021-11-01},
     pages = {JTu1A.99},
     publisher = {{Optica Publishing Group}},
     doi = {10.1364/FIO.2021.JTu1A.99},
     url = {https://opg.optica.org/abstract.cfm?uri=LS-2021-JTu1A.99},
     urldate = {2022-12-31},
     eventtitle = {Laser {{Science}}}
   }
   

3. Femtosecond Optical Tweezers for in Situ Tracking of Optically Directed Self-Assembly of Nanoclusters. D. Goswami, in (2020) [PDF] [BibTeX]

    BibTeX: @inproceedings{goswamiFemtosecondOpticalTweezers2020,
     title = {Femtosecond Optical Tweezers for in Situ Tracking of Optically Directed Self-Assembly of Nanoclusters},
     author = {Goswami, Debabrata},
     date = {2020-04-29},
     doi = {10.1021/scimeetings.0c03994},
     url = {https://www.morressier.com/article/5e735fe7cde2b641284aa286},
     urldate = {2020-07-11},
     eventtitle = {{{ACS Spring}} 2020 {{National Meeting}} \& {{Expo}}}
   }
   

4. Interplay of Thermal and Nonlinear Processes for Stable Optical Tweezers. D. Goswami, in Optical Trapping and Optical Micromanipulation XIX (SPIE, 2022), 12198, pp. 82–89 [Abstract] [PDF] [BibTeX]

   Abstract: Single-beam optical tweezers that use continuous wave (CW) lasers for trapping microscopic particles can be understood in terms of force-balancing light pressure from a tightly focused laser beam. High-repetition-rate femtosecond lasers for single-beam optical trapping research have matured as a technique and have garnered increasing interest. There are important differences between the theoretical models for femtosecond laser tweezers and the CW tweezers, e.g., in the sensitive detection of background-free two-photon fluorescence. The instantaneous trapping potential is due to the high peak power of each laser pulse, while the sustained stable trapping regime is a consequence of the high repetition rate of successive pulses. Simulating real-time scenarios for predicting optical trapping behavior continues to be a challenging problem. However, the capability and usefulness of optical tweezers setups with both CW and pulsed lasers are well established. For a tightly focused beam as used in an optical tweezer, cumulative heating can occur despite the minimal absorption cross-section of the trapping medium or the trapped particle, which reaches its maximum value near the focus. A temperature gradient from the laser focal spot is thus generated outwards from the laser focus in the medium, creating a refractive index gradient across the focusing region. The refractive index attains its minimum value at the focus, gradually increasing as a function of increasing distance from it. Since the trapping force and potential depend on the refractive index of the medium, the thermal effect impacts the force and potential of the trapped particle significantly. With CW lasers, computational evidence of temperature rise at the focus of optical tweezers has been posited, which, unfortunately, is not a feasible approach for ultrafast lasers, given their inherent computational complexities. A better understanding of high photon-flux induced processes and a working model of the single-beam optical tweezers that could address both CW and pulsed lasers would be ideal for elucidating the effects of this inherent thermal gradient of the optical tweezers. We demonstrate a framework that includes all possible nonlinear effects arising from high photon flux interactions and validate this with experimental results. Our approach allows a coherent and consistent treatment for both CW and ultrafast cases. We have the purely thermal nonlinear effects for the CW laser case, while for the ultrafast laser case, we include both the thermal and the Kerr type nonlinearities. Such a source-sensitive model is amenable to high throughput computations when coupled with a suitable paradigm for modeling experimental conditions as well.

    BibTeX: @inproceedings{goswamiInterplayThermalNonlinear2022,
     title = {Interplay of Thermal and Nonlinear Processes for Stable Optical Tweezers},
     booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIX}}},
     author = {Goswami, Debabrata},
     date = {2022-10-03},
     volume = {12198},
     pages = {82--89},
     publisher = {{SPIE}},
     doi = {10.1117/12.2633345},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/12198/121980D/Interplay-of-thermal-and-nonlinear-processes-for-stable-optical-tweezers/10.1117/12.2633345.full},
     urldate = {2022-12-31},
     eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIX}}}
   }
   

5. Reproducible High Performance Computing without Redundancy with Nix. R. Goswami, R. S., A. Goswami, S. Goswami, and D. Goswami, in 2022 Seventh International Conference on Parallel, Distributed and Grid Computing (PDGC) (2022), pp. 238–242 [Abstract] [BibTeX]

   Abstract: High performance computing (HPC) clusters are typically managed in a restrictive manner; the large user base makes cluster administrators unwilling to allow privilege escalation. Here we discuss existing methods of package management, including those which have been developed with scalability in mind, and enumerate the drawbacks and advantages of each management methodology. We contrast the paradigms of containerization via docker, virtualization via KVM, pod-infrastructures via Kubernetes, and specialized HPC packaging systems via Spack and identify key areas of neglect. We demonstrate how functional programming due to reliance on immutable states has been leveraged for deterministic package management via the nix-language expressions. We show its associated ecosystem is a prime candidate for HPC package management. We further develop guidelines and identify bottlenecks in the existing structure and present the methodology by which the nix ecosystem should be developed further as an optimal tool for HPC package management. We assert that the caveats of the nix ecosystem can easily mitigated by considerations relevant only to HPC systems, without compromising on functional methodology and features of the nix-language. We show that benefits of adoption in terms of generating reproducible derivations in a secure manner allow for workflows to be scaled across heterogeneous clusters. In particular, from the implementation hurdles faced during the compilation and running of the d-SEAMS scientific software engine, distributed as a nix-derivation on an HPC cluster, we identify communication protocols for working with SLURM and TORQUE user resource allocation queues. These protocols are heuristically defined and described in terms of the reference implementation required for queue-efficient nix builds.

    BibTeX: @inproceedings{goswamiReproducibleHighPerformance2022,
     title = {Reproducible {{High Performance Computing}} without {{Redundancy}} with {{Nix}}},
     booktitle = {2022 {{Seventh International Conference}} on {{Parallel}}, {{Distributed}} and {{Grid Computing}} ({{PDGC}})},
     author = {Goswami, Rohit and S., Ruhila and Goswami, Amrita and Goswami, Sonaly and Goswami, Debabrata},
     date = {2022-11},
     pages = {238--242},
     issn = {2573-3079},
     doi = {10.1109/PDGC56933.2022.10053342},
     eventtitle = {2022 {{Seventh International Conference}} on {{Parallel}}, {{Distributed}} and {{Grid Computing}} ({{PDGC}})}
   }
   

6. Semi-Supervised Approaches to Ultrafast Pulse Shaping. R. Goswami, A. Goswami, and D. Goswami, in ICOL-2019, K. Singh, A. K. Gupta, S. Khare, N. Dixit, and K. Pant, eds., Springer Proceedings in Physics (Springer, 2021), pp. 747–749 [Abstract] [PDF] [BibTeX]

   Abstract: Spatiotemporal control aspects of pulsed laser experiments rely on the ability to modulate the shape of the generated pulses efficiently. Drawing from current state-of-the-art theoretical aspects of computational simulations to reduce the sim-to-real bottlenecks, we devise a novel schematic for the generation of on-the-fly calibrated pulse trains with more accountability than existing techniques under the domain of optimal control theory. The techniques presented further diminish the divide between experiment and theory.

    BibTeX: @inproceedings{goswamiSemiSupervisedApproachesUltrafast2021,
     title = {Semi-{{Supervised Approaches}} to {{Ultrafast Pulse Shaping}}},
     booktitle = {{{ICOL-2019}}},
     author = {Goswami, Rohit and Goswami, Amrita and Goswami, Debabrata},
     editor = {Singh, Kehar and Gupta, A. K. and Khare, Sudhir and Dixit, Nimish and Pant, Kamal},
     date = {2021},
     series = {Springer {{Proceedings}} in {{Physics}}},
     pages = {747--749},
     publisher = {{Springer}},
     location = {{Singapore}},
     doi = {10.1007/978-981-15-9259-1_172},
     url = {10.1007/978-981-15-9259-1_172},
     isbn = {9789811592591}
   }
   

7. Sensing the Insensible Using Optical Schemes: Converting the Maze Problem into a Quantum Search Problem. D. Goswami, in Image Sensing Technologies: Materials, Devices, Systems, and Applications VII (International Society for Optics and Photonics, 2020), 11388, p. 113880L [Abstract] [PDF] [BibTeX]

   Abstract: Many large image processing and data processing scenarios can soon develop into maze problems requiring, say, finding the longest possible path, which are unresponsive, intractable, and challenging to analyze! Such maze problems, of which the traveling salesman decision problem is a special case, are of the Non-determinate Polynomial (NPcomplete) class of problems that are often impossible to solve with finite time and storage. We propose a novel methodology to approach this class of NP-complete problems. We convert a suitably formulated maze problem into a Quantum Search Problem (QSP), and the desired solutions are then sought using the iterative Grover’s Search Algorithm. Thus, we reformulate the entire class of such NP-problems into QSPs. Our current solution deals with two-dimensional perfect mazes with no closed loops. We encode all possible individual paths from the starting point of the maze into a quantum register. A quantum fitness operator applied to the register encodes each qubit with its fitness value. We propose the design of an optical oracle that marks all entities above a certain fitness value and uses the Grover search algorithm to find the optimal marked state in an iterative manner.

    BibTeX: @inproceedings{goswamiSensingInsensibleUsing2020,
     ids = {goswamiSensingInsensibleUsing2020a},
     title = {Sensing the Insensible Using Optical Schemes: Converting the Maze Problem into a Quantum Search Problem},
     shorttitle = {Sensing the Insensible Using Optical Schemes},
     booktitle = {Image {{Sensing Technologies}}: {{Materials}}, {{Devices}}, {{Systems}}, and {{Applications VII}}},
     author = {Goswami, Debabrata},
     date = {2020-04-23},
     volume = {11388},
     pages = {113880L},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10.1117/12.2563658},
     url = {10.1117/12.2563658},
     urldate = {2020-07-11},
     eventtitle = {Image {{Sensing Technologies}}: {{Materials}}, {{Devices}}, {{Systems}}, and {{Applications VII}}}
   }
   

8. Ultrafast Insights for Predictive Fragrance Compounding. D. Goswami, R. Goswami, A. Kumar Rawat, and D. Chakrabarty, in (2020) [PDF] [BibTeX]

    BibTeX: @inproceedings{goswamiUltrafastInsightsPredictive2020,
     title = {Ultrafast Insights for Predictive Fragrance Compounding},
     author = {Goswami, Debabrata and Goswami, Rohit and Kumar Rawat, Ashwini and Chakrabarty, Debojit},
     date = {2020-04-29},
     doi = {10.1021/scimeetings.0c03998},
     url = {https://www.morressier.com/article/5e73d6ce139645f83c2299c8},
     urldate = {2020-07-11},
     eventtitle = {{{ACS Spring}} 2020 {{National Meeting}} \& {{Expo}}}
   }
   

9. Using Femtosecond Coherent Oscillations to Unravel Dynamics of Complex Systems. D. Goswami, in ICOL-2019, K. Singh, A. K. Gupta, S. Khare, N. Dixit, and K. Pant, eds., Springer Proceedings in Physics (Springer, 2021), pp. 59–61 [Abstract] [PDF] [BibTeX]

   Abstract: Vibronic transitions of a molecular system in solution upon probing with ultrashort laser pulses (<40 fs), often creates coherent oscillations. These are either in the ground or excited state or in both the ground and excited states. Such vibrational coherence or coherent oscillation produced in the ground or excited states are often highly solvent dependent as these are characteristic of confinement and microheterogeneity in liquids.

    BibTeX: @inproceedings{goswamiUsingFemtosecondCoherent2021,
     title = {Using {{Femtosecond Coherent Oscillations}} to {{Unravel Dynamics}} of {{Complex Systems}}},
     booktitle = {{{ICOL-2019}}},
     author = {Goswami, Debabrata},
     editor = {Singh, Kehar and Gupta, A. K. and Khare, Sudhir and Dixit, Nimish and Pant, Kamal},
     date = {2021},
     series = {Springer {{Proceedings}} in {{Physics}}},
     pages = {59--61},
     publisher = {{Springer}},
     location = {{Singapore}},
     doi = {10/gjmht8},
     url = {10.1007/978-981-15-9259-1_14},
     isbn = {9789811592591}
   }
   

10. Modification of the Expression of L1-Norm of Coherence. M. Hazra and D. Goswami, in Quantum 2.0 Conference and Exhibition (2022), Paper QW2A.3 (Optica Publishing Group, 2022), p. QW2A.3 [Abstract] [PDF] [BibTeX]

    Abstract: Though a well-verified approach of quantifying quantum coherence is l1-norm, this is not normalized for a multi-qubit (multi-level) system. We propose a modification to show that the altered expression normalizes a multi-qubit (multi-level) system coherence with numerical studies.

     BibTeX: @inproceedings{hazraModificationExpressionL1norm2022,
      title = {Modification of the Expression of L1-Norm of Coherence},
      booktitle = {Quantum 2.0 {{Conference}} and {{Exhibition}} (2022), Paper {{QW2A}}.3},
      author = {Hazra, Manis and Goswami, Debabrata},
      date = {2022-06-13},
      pages = {QW2A.3},
      publisher = {{Optica Publishing Group}},
      doi = {10.1364/QUANTUM.2022.QW2A.3},
      url = {https://opg.optica.org/abstract.cfm?uri=QUANTUM-2022-QW2A.3},
      urldate = {2022-12-31},
      eventtitle = {Quantum 2.0}
    }
    

11. Advantage of Femtosecond Optical Tweezers. A. Singh, D. Kumar, K. K. Singh, and D. Goswami, in Frontiers in Optics + Laser Science 2022 (FIO, LS) (2022), Paper JW5A.26 (Optica Publishing Group, 2022), p. JW5A.26 [Abstract] [PDF] [BibTeX]

    Abstract: To highlight the advantage of femtosecond optical tweezers over conventional tweezers, we trapped 1µm diameter polystyrene beads suspended in water using a Ti:Sapphire laser.

     BibTeX: @inproceedings{singhAdvantageFemtosecondOptical2022,
      title = {Advantage of {{Femtosecond Optical Tweezers}}},
      booktitle = {Frontiers in {{Optics}} + {{Laser Science}} 2022 ({{FIO}}, {{LS}}) (2022), Paper {{JW5A}}.26},
      author = {Singh, Ajitesh and Kumar, Deepak and Singh, Krishna Kant and Goswami, Debabrata},
      date = {2022-10-17},
      pages = {JW5A.26},
      publisher = {{Optica Publishing Group}},
      url = {https://opg.optica.org/abstract.cfm?uri=FiO-2022-JW5A.26},
      urldate = {2022-12-31},
      eventtitle = {Frontiers in {{Optics}}}
    }
    

2019-2010

1. Thermal-Lens Spectroscopy in Binary Liquids Mixtures. I. Bhattacharyya, P. Kumar, and D. Goswami, in Frontiers in Optics 2010/Laser Science XXVI (2010), Paper FWX1 (Optical Society of America, 2010), p. FWX1 [Abstract] [PDF] [BibTeX]

   Abstract: Using femtosecond pump-probe thermal-lens (TL) spectroscopy, experiments in binary-mixtures are presented where trends in TL are modulated by physical and molecular properties. Deviations of experimental results from phenomenological models indicate possible underestimation of molecular interactions.

    BibTeX: @inproceedings{bhattacharyyaThermalLensSpectroscopyBinary2010,
     title = {Thermal-{{Lens}} Spectroscopy in Binary Liquids Mixtures},
     booktitle = {Frontiers in {{Optics}} 2010/{{Laser Science XXVI}} (2010), Paper {{FWX1}}},
     author = {Bhattacharyya, Indrajit and Kumar, Pardeep and Goswami, Debabrata},
     date = {2010-10-24},
     pages = {FWX1},
     publisher = {{Optical Society of America}},
     doi = {10/gf6c8z},
     url = {https://www.osapublishing.org/abstract.cfm?uri=FiO-2010-FWX1},
     urldate = {2019-08-14},
     eventtitle = {Frontiers in {{Optics}}}
   }
   

2. Insignificance of Relative Time Delay between Photons for a Ultrafast Two-Photon Process. A. Bose and D. Goswami, in 2012 International Conference on Fiber Optics and Photonics (PHOTONICS) (2012), pp. 1–3 [Abstract] [PDF] [BibTeX]

   Abstract: Exploring the possibility of temporally resolving dynamics in an ideal two-photon process (TPP) indicates that the existence of one-photon physical intermediate states is not a prerequisite for TPP. This study also sheds light on the phase dependence of TPP.

    BibTeX: @inproceedings{boseInsignificanceRelativeTime2012,
     title = {Insignificance of Relative Time Delay between Photons for a Ultrafast Two-Photon Process},
     booktitle = {2012 {{International Conference}} on {{Fiber Optics}} and {{Photonics}} ({{PHOTONICS}})},
     author = {Bose, A. and Goswami, D.},
     date = {2012-12},
     pages = {1--3},
     url = {http://pc.cd/pNhctalK},
     eventtitle = {2012 {{International Conference}} on {{Fiber Optics}} and {{Photonics}} ({{PHOTONICS}})}
   }
   

3. Sensing the Molecular Properties in Methanol and Its Binary Mixtures Using Time-Resolved Thermal Lens Spectrometer. S. Chakraborty, A. K. Rawat, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–3 [Abstract] [BibTeX]

   Abstract: Mode Mismatched Pump-Probe spectroscopic method was employed to examine the thermally induced nonlinear optical properties of methanol and its binary mixtures. The heat transfer mechanism in methanol and its binary mixtures with carbon tetrachloride (CCl4) at different concentrations of methanol is investigated. Methanol has the highest Thermal Lens (TL) signal, and CCl4 does not have any TL signal at all. However, the presence of CCl4 modulates the TL signal of the binary mixture. The time-domain shift in TL signal is observed for different concentrations of methanol, which indicates the unusual molecular behavior in the binary mixture.

    BibTeX: @inproceedings{chakrabortySensingMolecularProperties2019,
     title = {Sensing the {{Molecular Properties}} in {{Methanol}} and Its {{Binary Mixtures}} Using {{Time-Resolved Thermal Lens Spectrometer}}},
     booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Chakraborty, Subhajit and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2019-12},
     pages = {1--3},
     issn = {null},
     doi = {10.1109/WRAP47485.2019.9013697},
     eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

4. Control of Femtosecond Laser Driven Retro-Diels-Alder-like Reaction of Dicyclopentadiene. D. K. Das, T. Goswami, and D. Goswami, in Photonics 2010: Tenth International Conference on Fiber Optics and Photonics (International Society for Optics and Photonics, 2011), 8173, p. 81730O [Abstract] [PDF] [BibTeX]

   Abstract: Using femtosecond time resolved degenerate pump-probe mass spectrometry coupled with simple linearly chirped frequency modulated pulse, we elucidate that the dynamics of retro-Diels-Alder reaction of diclopentadiene (DCPD) to cyclopentadiene (CPD) in supersonic molecular beam occurs in ultrafast time scale. Negatively chirped pulse enhances the ion yield of CPD, as compared to positively chirped pulse. This indicates that by changing the frequency (chirp) of the laser pulse we can control the ion yield of a chemical reaction.

    BibTeX: @inproceedings{dasControlFemtosecondLaser2011,
     title = {Control of Femtosecond Laser Driven Retro-{{Diels-Alder-like}} Reaction of Dicyclopentadiene},
     booktitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Das, Dipak Kumar and Goswami, Tapas and Goswami, Debabrata},
     date = {2011-08-23},
     volume = {8173},
     pages = {81730O},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/dsc8s7},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8173/81730O/Control-of-femtosecond-laser-driven-retro-Diels-Alder-like-reaction/10.1117/12.897909.short},
     urldate = {2019-08-13},
     eventtitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}}
   }
   

5. Direct Observation of Diatoms Pair Formation in Aqueous Solution Under Laser Scanning Fluorescence Microscopy. D. Das and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. Tu2B.3 [Abstract] [PDF] [BibTeX]

   Abstract: We show important applications of our imaging technique in visualizing the morphology as well as division of diatoms in aqueous solution. The technique involves the efficient detection of the auto-fluorescence from chloroplast and shell structure through laser scanning confocal microscopy.

    BibTeX: @inproceedings{dasDirectObservationDiatoms2016,
     title = {Direct {{Observation}} of {{Diatoms Pair Formation}} in {{Aqueous Solution Under Laser Scanning Fluorescence Microscopy}}},
     booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Das, Dhiman and Goswami, Debabrata},
     date = {2016},
     pages = {Tu2B.3},
     publisher = {{OSA}},
     location = {{Kharagpur}},
     doi = {10/gf5mrq},
     url = {https://my.pcloud.com/publink/show?code=XZrNxr7ZTM0YMQbaakBFrDr1GOUzFXGBIn6V},
     urldate = {2019-08-01},
     eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
     isbn = {978-1-943580-22-4}
   }
   

6. Sensing near the Liquid:Liquid Interface Remotely via Ultrafast Pump Probe Study. D. K. Das, K. Makhal, and D. Goswami, in 2015 Workshop on Recent Advances in Photonics (WRAP) (2015), pp. 1–4 [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast pump-probe technique has been invoked to understand the liquid:liquid interface by using a cyanine dye dissolved in dimethyl sulfoxide (DMSO), interfaced with neat diethyl-ether (Et2O). We show that the dynamics of the dye gets slow down on moving from the bulk dye solution in DMSO towards the interface with neat-diethyl ether. Hence we get an alternate picture of interface by looking at the time constants. Four time constants were used for fitting the experimental data which are assigned to be coherent artifact, vibrational cooling, intermediate state time and finally ground state recovery time. The drastic change in signal was observed at a distance of 0.1 mm from the interface. The decreasing time constants from bulk to near interfaced solution strongly suggests involvement of heterogeneity in the system because of the penetration of diethyl ether through the interface into the DMSO layer where the dye is dissolved, which strongly affects the dynamics at near the interface of the DMSO with neat-diethyl ether layer (at 0.1 mm distance from the interface).

    BibTeX: @inproceedings{dasSensingLiquidLiquid2015,
     title = {Sensing near the Liquid:Liquid Interface Remotely via Ultrafast Pump Probe Study},
     shorttitle = {Sensing near the Liquid},
     booktitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Das, D. K. and Makhal, K. and Goswami, D.},
     date = {2015-12},
     pages = {1--4},
     doi = {10/gf5msb},
     url = {https://my.pcloud.com/publink/show?code=XZfAxr7ZEoKkOTQY1W73Rb0uatplJzuKxRvV},
     eventtitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

7. Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De, D. Roy, and D. Goswami, in Multiphoton Microscopy in the Biomedical Sciences X (International Society for Optics and Photonics, 2010), 7569, p. 756929 [Abstract] [PDF] [BibTeX]

   Abstract: The broad spectral window of an ultra-short laser pulse and the broad overlapping multiphoton absorption spectra of common fluorophores restrict selective excitation of one fluorophore in presence of others during multiphoton fluorescence microscopy. Also spatial resolution, limited by the fundamental diffraction limit, is governed by the beam profile. Here we show our recent work on selective fluorescence suppression using a femtosecond pulse-pair excitation which is equivalent to amplitude shaping using a pulse shaper. In addition, prospects of laser beam shaping in imaging are also briefly discussed.

    BibTeX: @inproceedings{deSpatiotemporalControlMultiphoton2010,
     title = {Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
     booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2010-02-26},
     volume = {7569},
     pages = {756929},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/c529hw},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7569/756929/Spatio-temporal-control-in-multiphoton-fluorescence-laser-scanning-microscopy/10.1117/12.838287.short},
     urldate = {2019-08-14},
     eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}}
   }
   

8. Towards Stable Trapping of Single Macromolecules in Solution. A. K. De, D. Roy, and D. Goswami, in Optical Trapping and Optical Micromanipulation VII (International Society for Optics and Photonics, 2010), 7762, p. 776203 [Abstract] [PDF] [BibTeX]

   Abstract: The implementation of high instantaneous peak power of a femtosecond laser pulse at moderate time-averaged power (~10 mW) to trap latex nanoparticles, which is otherwise impossible with continuous wave illumination at similar power level, has recently been shown [De, A. K., Roy, D., Dutta, A. and Goswami, D. "Stable optical trapping of latex nanoparticles with ultrashort pulsed illumination", Appd. Opt., 48, G33 (2009)]. However, direct measurement of the instantaneous trapping force/stiffness due to a single pulse has been unsuccessful due to the fleeting existence (~100 fs) of the laser pulse compared with the much slower time scale associated with the available trapping force/stiffness calibration techniques, as discussed in this proceeding article. We also demonstrate trapping of quantum dots having dimension similar to macromolecules.

    BibTeX: @inproceedings{deStableTrappingSingle2010,
     title = {Towards Stable Trapping of Single Macromolecules in Solution},
     booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2010-08-27},
     volume = {7762},
     pages = {776203},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/ckqvtz},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7762/776203/Towards-stable-trapping-of-single-macromolecules-in-solution/10.1117/12.862364.short},
     urldate = {2019-08-14},
     eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}}
   }
   

9. Manifesting the Effects of Thermal Nonlinearity in Optical Trapping for Rayleigh Regime. T. Gaur, S. N. Bandyopadhyay, and D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (IEEE, 2019), pp. 1–5 [Abstract] [PDF] [BibTeX]

   Abstract: Since long the thermal effects have not been much explored in the optical trapping theory, in this paper, we are establishing the effects of optically induced thermal nonlinearity in the medium of optical trapping in the Rayleigh regime for both continuous wave and a pulsed laser. For a single beam, optical tweezers with high numerical aperture (N.A.) objectives are used as a routine. In such a tight focusing scenario, both optical nonlinearity and thermal effects may prevail in the cases of continuous wave (C.W.) and pulsed laser-mediated optical trapping events. In this paper we will introduce the effects sequentially, starting from optical nonlinearity and methods to implement this effect and subsequently introduce the thermal nonlinearity in the medium. The effects are significantly different when compared between CW and pulsed optical tweezers and will be discussed in detail in this paper.

    BibTeX: @inproceedings{gaurManifestingEffectsThermal2019,
     title = {Manifesting the {{Effects}} of {{Thermal Nonlinearity}} in {{Optical Trapping}} for {{Rayleigh Regime}}},
     booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     author = {Gaur, Tushar and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2019-03},
     pages = {1--5},
     publisher = {{IEEE}},
     location = {{New Delhi, India}},
     doi = {10/gf5mqf},
     url = {https://my.pcloud.com/publink/show?code=XZqaxr7ZmnVNxAn4Y4mRbGS3d4A7FjmCWEv7},
     urldate = {2019-08-01},
     eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     isbn = {978-90-825987-5-9}
   }
   

10. Demonstrating a Nano Viscometer Using Femtosecond Laser Induced Photo-Thermal Effect. D. Goswami, in 2015 Workshop on Recent Advances in Photonics (WRAP) (2015), pp. 1–4 [Abstract] [PDF] [BibTeX]

    Abstract: We present a new method to utilize photo-thermal effect at nano-volume dimension, to measure viscosity, which could be useful to eventually correlate to in-vivo conditions. We present our measurements using high repetition rate low average power femtosecond laser induced conditions under which the photo-thermal effect is highly influence by the convective mode of heat transfer. This is especially important in absorbing liquids. This is unlike the typical photo-thermal conditions not involving such ultrashort pulses. Typical thermal processes involve only conductive mode of heat transfer and are phenomenological in nature. Inclusion of convective mode results in some additional molecular characteristics to the thermal process. We measure the traditional thermal lens studies with femtosecond pulse train through geometric beam divergence of a collimated laser beam co-propagating with the focused heating laser beam. The refractive index gradient in the sample due to the focused heating laser creates a thermal lens, which is measured. On the other hand, the same heat gradient from the focusing heating laser beam generates a change in local viscosity in the medium, which changes the trapped stiffness of an optically trapped microsphere in its vicinity. We use co-propagating femtosecond train of laser pulses of wavelength 1560 nm and 780 nm for these experiments. From the bulk thermal studies, we show that use of water as sample provides us the advantage to use conductive mode of heat transfer even with femtosecond pulse train excitation.

     BibTeX: @inproceedings{goswamiDemonstratingNanoViscometer2015,
      title = {Demonstrating a Nano Viscometer Using Femtosecond Laser Induced Photo-Thermal Effect},
      booktitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Goswami, D.},
      date = {2015-12},
      pages = {1--4},
      doi = {10/gf5msc},
      url = {https://my.pcloud.com/publink/show?code=XZUGxr7ZadBLrqnQAXVhW2jQ8UVesyuCjpny},
      eventtitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

11. Femtosecond Laser Induced Spatiotemporal Control for Remote Sensing and Computation at Nanoscale. D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (IEEE, 2019), pp. 1–1 [PDF] [BibTeX]

     BibTeX: @inproceedings{goswamiFemtosecondLaserInduced2019,
      title = {Femtosecond {{Laser Induced Spatiotemporal Control}} for {{Remote Sensing}} and {{Computation}} at {{Nanoscale}}},
      booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
      author = {Goswami, Debabrata},
      date = {2019-03},
      pages = {1--1},
      publisher = {{IEEE}},
      location = {{New Delhi, India}},
      doi = {10/gf5mp6},
      url = {https://my.pcloud.com/publink/show?code=XZyvxr7ZOeecG9i7bDyhB3UKkH2KEbJ5Bd87},
      urldate = {2019-08-01},
      eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
      isbn = {978-90-825987-5-9}
    }
    

12. Femtosecond Spatiotemporal Control with Multiple Knobs. D. Goswami, in CLEO/QELS: 2010 Laser Science to Photonic Applications (2010), pp. 1–2 [Abstract] [BibTeX]

    Abstract: For controlling non-resonant molecular fragmentation process, simultaneous effect of chirp and polarization of a femtosecond pulse is mutually independent. For multiphoton fluorescence microscopy and optical tweezers with high-repetition-rate lasers, inter-pulse separation and polarization is important.

     BibTeX: @inproceedings{goswamiFemtosecondSpatiotemporalControl2010,
      title = {Femtosecond Spatiotemporal Control with Multiple Knobs},
      booktitle = {{{CLEO}}/{{QELS}}: 2010 {{Laser Science}} to {{Photonic Applications}}},
      author = {Goswami, D.},
      date = {2010-05},
      pages = {1--2},
      doi = {10/gf6c82},
      eventtitle = {{{CLEO}}/{{QELS}}: 2010 {{Laser Science}} to {{Photonic Applications}}}
    }
    

13. Fluorescence Advantages with Microscopic Spatiotemporal Control. D. Goswami, D. Roy, and A. K. De, in Design and Quality for Biomedical Technologies VI (International Society for Optics and Photonics, 2013), 8573, p. 857302 [Abstract] [PDF] [BibTeX]

    Abstract: We present a clever design concept of using femtosecond laser pulses in microscopy by selective excitation or de-excitation of one fluorophore over the other overlapping one. Using either a simple pair of femtosecond pulses with variable delay or using a train of laser pulses at 20-50 Giga-Hertz excitation, we show controlled fluorescence excitation or suppression of one of the fluorophores with respect to the other through wave-packet interference, an effect that prevails even after the fluorophore coherence timescale. Such an approach can be used both under the single-photon excitation as well as in the multi-photon excitation conditions resulting in effective higher spatial resolution. Such high spatial resolution advantage with broadband-pulsed excitation is of immense benefit to multi-photon microscopy and can also be an effective detection scheme for trapped nanoparticles with near-infrared light. Such sub-diffraction limit trapping of nanoparticles is challenging and a two-photon fluorescence diagnostics allows a direct observation of a single nanoparticle in a femtosecond high-repetition rate laser trap, which promises new directions to spectroscopy at the single molecule level in solution. The gigantic peak power of femtosecond laser pulses at high repetition rate, even at low average powers, provide huge instantaneous gradient force that most effectively result in a stable optical trap for spatial control at sub-diffraction limit. Such studies have also enabled us to explore simultaneous control of internal and external degrees of freedom that require coupling of various control parameters to result in spatiotemporal control, which promises to be a versatile tool for the microscopic world.

     BibTeX: @inproceedings{goswamiFluorescenceAdvantagesMicroscopic2013,
      title = {Fluorescence Advantages with Microscopic Spatiotemporal Control},
      booktitle = {Design and {{Quality}} for {{Biomedical Technologies VI}}},
      author = {Goswami, Debabrata and Roy, Debjit and De, Arijit K.},
      date = {2013-03-13},
      volume = {8573},
      pages = {857302},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5npw},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8573/857302/Fluorescence-advantages-with-microscopic-spatiotemporal-control/10.1117/12.2009500.short},
      urldate = {2019-08-02},
      eventtitle = {Design and {{Quality}} for {{Biomedical Technologies VI}}}
    }
    

14. Highly Nonlinear Femtosecond Processes in Liquid Phase: Water Cluster Raman Spectra and Microheterogeneity Induced Coherent Oscillations. D. Goswami, in 12th International Conference on Fiber Optics and Photonics (OSA, 2014), p. T4C.2 [Abstract] [PDF] [BibTeX]

    Abstract: Stokes region of water supercontinuum shows explicit water-cluster Raman features arising at high laser intensities. Near-infrared degenerate pump-probe of a cyanine dye shows coherent oscillations only in binary liquid mixtures at sub-40 femtosecond resolution.

     BibTeX: @inproceedings{goswamiHighlyNonlinearFemtosecond2014,
      title = {Highly {{Nonlinear Femtosecond Processes}} in {{Liquid Phase}}: {{Water Cluster Raman Spectra}} and {{Microheterogeneity Induced Coherent Oscillations}}},
      shorttitle = {Highly {{Nonlinear Femtosecond Processes}} in {{Liquid Phase}}},
      booktitle = {12th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Goswami, Debabrata},
      date = {2014},
      pages = {T4C.2},
      publisher = {{OSA}},
      location = {{Kharagpur}},
      doi = {10/gf5ms5},
      url = {https://my.pcloud.com/publink/show?code=XZDGxr7ZuCkX5dqDlQ4Cww6kKhi4up5N58Wy},
      urldate = {2019-08-01},
      eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
      isbn = {978-1-55752-882-7}
    }
    

15. Measurement Constraints in Laser Based Thermal Lens Experiments. D. Goswami and P. Kumar, in International Conference on Optics and Photonics 2015 (International Society for Optics and Photonics, 2015), 9654, p. 965406 [Abstract] [PDF] [BibTeX]

    Abstract: Importance of various measurement schemes in studying thermal lens (TL) signal for laser based TL experiments is explored. We show that two different measurement schemes can result in two contrasting outcomes. In one experiment, two measurement schemes show diverging results for TL signal measurements, which gives a convoluted result and in the other experiment, the two measurement schemes give a converging result.

     BibTeX: @inproceedings{goswamiMeasurementConstraintsLaser2015,
      title = {Measurement Constraints in Laser Based Thermal Lens Experiments},
      booktitle = {International {{Conference}} on {{Optics}} and {{Photonics}} 2015},
      author = {Goswami, Debabrata and Kumar, Pardeep},
      date = {2015-06-15},
      volume = {9654},
      pages = {965406},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5msn},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9654/965406/Measurement-constraints-in-laser-based-thermal-lens-experiments/10.1117/12.2192167.short},
      urldate = {2019-08-01},
      eventtitle = {International {{Conference}} on {{Optics}} and {{Photonics}} 2015}
    }
    

16. Quantum Distributed Computing with Shaped Laser Pulses. R. Goswami and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. W4C.3 [Abstract] [BibTeX]

    Abstract: Shaped laser pulses can control decoherence under quantum adiabatic method of logic operations to result in a possible scalable quantum computer by distributing the computing load on a set of optically adiabatic quantum computing nodes.

     BibTeX: @inproceedings{goswamiQuantumDistributedComputing2016,
      title = {Quantum {{Distributed Computing}} with {{Shaped Laser Pulses}}},
      booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Goswami, Rohit and Goswami, Debabrata},
      date = {2016},
      pages = {W4C.3},
      publisher = {{OSA}},
      location = {{Kanpur}},
      doi = {10/gf5mrr},
      eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
      isbn = {978-1-943580-22-4}
    }
    

17. Qubit Network Barriers to Deep Learning. R. Goswami, A. Goswami, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–3 [Abstract] [BibTeX]

    Abstract: The popularity of artificial neural networks (ANNs) of great depth and Quantum computing have led to many speculations as to their convergence. We enumerate barriers to utilizing qubit networks for deep learning architectures. We also describe the criteria for an effective usage of qubit networks and then assert that the bottleneck in their implementation is a lack of quantum algorithms for utilizing the topology of a deep neural network.

     BibTeX: @inproceedings{goswamiQubitNetworkBarriers2019,
      title = {Qubit {{Network Barriers}} to {{Deep Learning}}},
      booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Goswami, Rohit and Goswami, Amrita and Goswami, Debabrata},
      date = {2019-12},
      pages = {1--3},
      issn = {null},
      doi = {10.1109/WRAP47485.2019.9013687},
      eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

18. Sensitive Detection of Phase Separation with Femtosecond Thermal Lens Spectroscopy. S. Goswami, S. Singhal, A. Banerjee, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–2 [Abstract] [BibTeX]

    Abstract: Femtosecond Thermal Lens Spectroscopy (FTLS) has been developed to a level of sensitivity that can have molecule specific response due to convection as demonstrated experimentally and theoretically. Within this framework, we show here that it is possible to use this technique for sensitive detection of liquid versus gas phase. Experimental demonstration is made with a single beam FTLS experiment of traces of iodine in pentane mixture in liquid versus its vapor phase.

     BibTeX: @inproceedings{goswamiSensitiveDetectionPhase2019,
      title = {Sensitive {{Detection}} of {{Phase Separation}} with {{Femtosecond Thermal Lens Spectroscopy}}},
      booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Goswami, Sonaly and Singhal, Sumit and Banerjee, Arup and Goswami, Debabrata},
      date = {2019-12},
      pages = {1--2},
      issn = {null},
      doi = {10.1109/WRAP47485.2019.9013833},
      eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

19. Space Filling Curves: Heuristics For Semi Classical Lasing Computations. R. Goswami, A. Goswami, and D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (IEEE, 2019), pp. 1–4 [Abstract] [PDF] [BibTeX]

    Abstract: For semi classical lasing, the FDTD (finite difference time domain) formulation including nonlinearities is often used. We determine the computational efficiency of such schemes quantitatively and present a hueristic based on space filling curves to minimize complexity. The sparse matrix kernel is shown to be optimized by the utilization of Bi-directional Incremental Compressed Row Storage (BICRS). Extensions to high performance clusters and parallelization are also derived.

     BibTeX: @inproceedings{goswamiSpaceFillingCurves2019,
      title = {Space {{Filling Curves}}: {{Heuristics For Semi Classical Lasing Computations}}},
      shorttitle = {Space {{Filling Curves}}},
      booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
      author = {Goswami, Rohit and Goswami, Amrita and Goswami, Debabrata},
      date = {2019-03},
      pages = {1--4},
      publisher = {{IEEE}},
      location = {{New Delhi, India}},
      doi = {10/gf5mqk},
      url = {https://my.pcloud.com/publink/show?code=XZ8vxr7ZHFxXSXuD2J4ntMcQoyPGXFodmegy},
      urldate = {2019-08-01},
      eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
      isbn = {978-90-825987-5-9}
    }
    

20. Structured Interferometry Features in Femtosecond Supercontinuum: Towards Better Understanding of Supercontinuum for Bio Applications. D. Goswami, S. Dinda, and S. N. Bandyopadhyay, in Optical Biopsy XV: Toward Real-Time Spectroscopic Imaging and Diagnosis (International Society for Optics and Photonics, 2017), 10060, p. 1006019 [Abstract] [PDF] [BibTeX]

    Abstract: We report structured interferometry features in femtosecond supercontinuum generated with power near to supercontinuum generation threshold. We argue that these structures arise from the coherent superposition of supercontinuum generated from different sources of supercontinuum as pulse split into two daughter pulses. Increase in input pulse energy creates several more temporal pulse fragments and disrupts interference resulting in the typical feature of continuous broad supercontinuum. Such an understanding of supercontinuum generation process is critical to the use of supercontinuum as the light source for use in understanding the time dynamics and imaging of bio systems.

     BibTeX: @inproceedings{goswamiStructuredInterferometryFeatures2017,
      title = {Structured Interferometry Features in Femtosecond Supercontinuum: Towards Better Understanding of Supercontinuum for Bio Applications},
      shorttitle = {Structured Interferometry Features in Femtosecond Supercontinuum},
      booktitle = {Optical {{Biopsy XV}}: {{Toward Real-Time Spectroscopic Imaging}} and {{Diagnosis}}},
      author = {Goswami, Debabrata and Dinda, Sirshendu and Bandyopadhyay, Soumendra N.},
      date = {2017-02-17},
      volume = {10060},
      pages = {1006019},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5mrd},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10060/1006019/Structured-interferometry-features-in-femtosecond-supercontinuum--towards-better-understanding/10.1117/12.2253561.short},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Biopsy XV}}: {{Toward Real-Time Spectroscopic Imaging}} and {{Diagnosis}}}
    }
    

21. Visualizing Colloidal Aggregation with Femtosecond Optical Tweezers. D. Goswami, in Optical Trapping and Optical Micromanipulation XVI (International Society for Optics and Photonics, 2019), 11083, p. 110832C [Abstract] [PDF] [BibTeX]

    Abstract: Optical tweezers manipulate microscopic objects using forces arising from the subtle interplay of optical scattering and gradient forces of highly focused laser beams. Unlike conventional backscatter signal for optical tweezers, the twophoton fluorescence (TPF) trapping signal from femtosecond optical tweezers (FOTs) shows a slow counterintuitive decay, when the trapped particles are not entirely within the laser-illuminated volume. A change in the corner frequency of FOT is also noted with the TPF technique. These observations are evident even at low average powers. The high peak powers trap not only single microspheres but also encourage optically directed self-assembly. We use TPF signatures of trapped particles to show the existence of a directed self-assembly process and elucidate the structural dynamics during the process of cluster formation.

     BibTeX: @inproceedings{goswamiVisualizingColloidalAggregation2019,
      title = {Visualizing Colloidal Aggregation with Femtosecond Optical Tweezers},
      booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XVI}}},
      author = {Goswami, Debabrata},
      date = {2019-09-09},
      volume = {11083},
      pages = {110832C},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf874x},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11083/110832C/Visualizing-colloidal-aggregation-with-femtosecond-optical-tweezers/10.1117/12.2528518.short},
      urldate = {2019-10-02},
      eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XVI}}}
    }
    

22. Spectrally Resolved Femtosecond Photon Echo Spectroscopy of Astaxanthin. A. Kumar, S. K. K. Kumar, A. Gupta, and D. Goswami, in Photonics 2010: Tenth International Conference on Fiber Optics and Photonics (International Society for Optics and Photonics, 2011), 8173, p. 817325 [Abstract] [PDF] [BibTeX]

    Abstract: We have studied the coherence and population dynamics of Astaxanthin solution in methanol and acetonitrile by spectrally resolving their photon echo signals. Our experiments indicate that methanol has a much stronger interaction with the ultrafast dynamics of Astaxanthin in comparison to that of acetonitrile.

     BibTeX: @inproceedings{kumarSpectrallyResolvedFemtosecond2011,
      title = {Spectrally Resolved Femtosecond Photon Echo Spectroscopy of Astaxanthin},
      booktitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Kumar, Ajitesh and Kumar, S. K. Karthick and Gupta, Aditya and Goswami, Debabrata},
      date = {2011-08-23},
      volume = {8173},
      pages = {817325},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/fs3jxj},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8173/817325/Spectrally-resolved-femtosecond-photon-echo-spectroscopy-of-astaxanthin/10.1117/12.899781.short},
      urldate = {2019-08-02},
      eventtitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}}
    }
    

23. Thermal-Lens Spectroscopy in Binary Liquids Mixtures: Effect of Isotope Substitution. P. Kumar, I. Bhattacharyya, and D. Goswami, in Frontiers in Optics 2011/Laser Science XXVII (2011), Paper JTuA25 (Optical Society of America, 2011), p. JTuA25 [Abstract] [PDF] [BibTeX]

    Abstract: Using femtosecond pump-probe thermal lens (TL) spectroscopy, we show that the effect of isotope substitution can be monitored through a modulation of TL signals in binary liquids showing the important of molecular properties on TL.

     BibTeX: @inproceedings{kumarThermalLensSpectroscopyBinary2011,
      title = {Thermal-{{Lens Spectroscopy}} in {{Binary Liquids Mixtures}}: {{Effect}} of {{Isotope Substitution}}},
      shorttitle = {Thermal-{{Lens Spectroscopy}} in {{Binary Liquids Mixtures}}},
      booktitle = {Frontiers in {{Optics}} 2011/{{Laser Science XXVII}} (2011), Paper {{JTuA25}}},
      author = {Kumar, Pardeep and Bhattacharyya, Indrajit and Goswami, Debabrata},
      date = {2011-10-16},
      pages = {JTuA25},
      publisher = {{Optical Society of America}},
      doi = {10/gf5nqg},
      url = {https://www.osapublishing.org/abstract.cfm?uri=FiO-2011-JTuA25},
      urldate = {2019-08-02},
      eventtitle = {Frontiers in {{Optics}}}
    }
    

24. Reverse Saturable Absorption Followed by Anomalous Saturable Absorption in Rhodamine-700. K. Makhal, S. Maurya, and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. Tu5D.2 [Abstract] [PDF] [BibTeX]

    Abstract: Anomalous SA (saturable absorption) in presence of reverse saturable absorption (RSA) in Rhodamine-700 is reported employing Z-scan with 100 ns, 250 Hz pulses in methanol. SA is observed only at a particular intensity range otherwise RSA survives.

     BibTeX: @inproceedings{makhalReverseSaturableAbsorption2016,
      title = {Reverse {{Saturable Absorption}} Followed by {{Anomalous Saturable Absorption}} in {{Rhodamine-700}}},
      booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Makhal, Krishnandu and Maurya, Sidharth and Goswami, Debabrata},
      date = {2016},
      pages = {Tu5D.2},
      publisher = {{OSA}},
      location = {{Kharagpur}},
      doi = {10/gf5mrp},
      url = {https://www.osapublishing.org/abstract.cfm?URI=Photonics-2016-Tu5D.2},
      urldate = {2019-08-01},
      eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
      isbn = {978-1-943580-22-4}
    }
    

25. Study of Self Defocusing in Liquids Using Single Beam Z-scan with High Repetition Rate Laser Pulses. S. K. Maurya, S. Singhal, and D. Goswami, in International Conference on Fibre Optics and Photonics (OSA, 2012), p. TPo.44 [Abstract] [PDF] [BibTeX]

    Abstract: We report the behavior of nonlinear refraction property of solvent using femtosecond high repetition rate laser pulses with close aperture z scan technique. Self defocusing due to HRR pulses highly depend on viscosity and density of the systems.

     BibTeX: @inproceedings{mauryaStudySelfDefocusing2012,
      title = {Study of Self Defocusing in Liquids Using Single Beam {{Z-scan}} with {{High}} Repetition Rate Laser Pulses},
      booktitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
      author = {Maurya, Sandeep Kumar and Singhal, Sumit and Goswami, Debabrata},
      date = {2012},
      pages = {TPo.44},
      publisher = {{OSA}},
      location = {{Chennai}},
      doi = {10/gf5nqb},
      url = {https://www.osapublishing.org/abstract.cfm?URI=Photonics-2012-TPo.44},
      urldate = {2019-08-02},
      eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}}
    }
    

26. Calibration of Femtosecond Optical Tweezers as a Sensitive Thermometer. D. Mondal and D. Goswami, in Optical Trapping and Optical Micromanipulation XII (International Society for Optics and Photonics, 2015), 9548, p. 95481N [Abstract] [PDF] [BibTeX]

    Abstract: We present cumulative perturbation effects of femtosecond laser pulses on an optical tweezer. Our experiments involve a dual wavelength high repetition rate femtosecond laser, one at the non-heating wavelength of 780 nm while the other at 1560 nm to cause heating in the trapped volume under low power (100-800 μW) conditions. The 1560 nm high repetition rate laser acts as a resonant excitation source for the vibrational combination band of the hydroxyl group (OH) of water, which helps create the local heating effortlessly within the trapping volume. With such an experimental system, we are the first to observe direct effect of temperature on the corner frequency deduced from power spectrum. We can, thus, control and measure temperature precisely at the optical trap. This observation has lead us to calculate viscosity as well as temperature in the vicinity of the trapping zone. These experimental results also support the well-known fact that the nature of Brownian motion is the response of the optically trapped bead from the temperature change of surroundings. Temperature rise near the trapping zone can significantly change the viscosity of the medium. However, we notice that though the temperature and viscosity are changing as per our corner frequency calculations, the trap stiffness remains the same throughout our experiments within the temperature range of about 20 K.

     BibTeX: @inproceedings{mondalCalibrationFemtosecondOptical2015,
      title = {Calibration of Femtosecond Optical Tweezers as a Sensitive Thermometer},
      booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XII}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2015-08-25},
      volume = {9548},
      pages = {95481N},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5msk},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9548/95481N/Calibration-of-femtosecond-optical-tweezers-as-a-sensitive-thermometer/10.1117/12.2187097.short},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XII}}}
    }
    

27. Controlling the Effect on Solvent by Resonant Excitation in Femtosecond Optical Tweezer. D. Mondal and D. Goswami, in Optics in the Life Sciences (OSA, 2015), p. OtT4E.3 [Abstract] [PDF] [BibTeX]

    Abstract: Observation of direct effect of temperature rise in water around optical trap center is presented. Irradiation of IR laser with low power during pulsed 780 nm trapping significantly changes solvent viscosity keeping trap stiffness unaffected.

     BibTeX: @inproceedings{mondalControllingEffectSolvent2015,
      title = {Controlling the Effect on Solvent by Resonant Excitation in Femtosecond Optical Tweezer},
      booktitle = {Optics in the {{Life Sciences}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2015},
      pages = {OtT4E.3},
      publisher = {{OSA}},
      location = {{Vancouver}},
      doi = {10/gf5msw},
      url = {https://www.osapublishing.org/abstract.cfm?URI=OTA-2015-OtT4E.3},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping Applications}}},
      isbn = {978-1-55752-954-1}
    }
    

28. Elucidating Two Photon FRET and Its Application through Femtosecond Optical Tweezers. D. Mondal, D. Roy, S. Dinda, A. Singh, and D. Goswami, in Advanced Photonics 2016 (IPR, NOMA, Sensors, Networks, SPPCom, SOF) (OSA, 2016), p. NoTu2D.4 [Abstract] [PDF] [BibTeX]

    Abstract: We have observed two photon fluorescence resonance energy transfer (FRET) from optically trapped bead coated with multiple dyes. The fluorescence obtained from trapped particles is useful to measure biomechanical property of that confined system.

     BibTeX: @inproceedings{mondalElucidatingTwoPhoton2016,
      title = {Elucidating {{Two Photon FRET}} and Its Application through Femtosecond Optical Tweezers},
      booktitle = {Advanced {{Photonics}} 2016 ({{IPR}}, {{NOMA}}, {{Sensors}}, {{Networks}}, {{SPPCom}}, {{SOF}})},
      author = {Mondal, Dipankar and Roy, Debjit and Dinda, Sirshendu and Singh, Ajitesh and Goswami, Debabrata},
      date = {2016},
      pages = {NoTu2D.4},
      publisher = {{OSA}},
      location = {{Vancouver}},
      doi = {10/gf5mr4},
      url = {https://www.osapublishing.org/abstract.cfm?URI=NOMA-2016-NoTu2D.4},
      urldate = {2019-08-01},
      eventtitle = {Novel {{Optical Materials}} and {{Applications}}},
      isbn = {978-1-943580-14-9}
    }
    

29. Femtosecond Optical Tweezers as Sensitive Nano-Thermometer. D. Mondal and D. Goswami, in Frontiers in Optics 2016 (OSA, 2016), p. JTh2A.117 [Abstract] [PDF] [BibTeX]

    Abstract: Nano-volume temperature rise around optical trap is measured by exploiting non radiative relaxation in solvents. Co-propagating 1560 nm femtosecond laser pulses change solvent temperature and viscosity while trap-stiffness is unaffected during 780 nm trapping.

     BibTeX: @inproceedings{mondalFemtosecondOpticalTweezers2016,
      title = {Femtosecond Optical Tweezers as Sensitive Nano-Thermometer},
      booktitle = {Frontiers in {{Optics}} 2016},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016},
      pages = {JTh2A.117},
      publisher = {{OSA}},
      location = {{Rochester, New York}},
      doi = {10/gf5mrv},
      url = {https://www.osapublishing.org/abstract.cfm?URI=FiO-2016-JTh2A.117},
      urldate = {2019-08-01},
      eventtitle = {Frontiers in {{Optics}}},
      isbn = {978-1-943580-19-4}
    }
    

30. Microrheology Study of Aqueous Suspensions of Laponite Using Femtosecond Optical Tweezers. D. Mondal, A. Jha, Y. M. Joshi, and D. Goswami, in Optics in the Life Sciences Congress (2017), Paper OtW2E.1 (Optical Society of America, 2017), p. OtW2E.1 [Abstract] [PDF] [BibTeX]

    Abstract: We have observed microrheological aging dynamics of Laponite® suspensions using femtosecond optical tweezers (FOTs). Our on the fly calibration in time domain has been used to probe microscopic structural changes in the complex fluid.

     BibTeX: @inproceedings{mondalMicrorheologyStudyAqueous2017,
      title = {Microrheology {{Study}} of {{Aqueous Suspensions}} of {{Laponite}} Using {{Femtosecond Optical Tweezers}}},
      booktitle = {Optics in the {{Life Sciences Congress}} (2017), Paper {{OtW2E}}.1},
      author = {Mondal, Dipankar and Jha, Anushka and Joshi, Yogesh M. and Goswami, Debabrata},
      date = {2017-04-02},
      pages = {OtW2E.1},
      publisher = {{Optical Society of America}},
      doi = {10/gf5mrb},
      url = {https://www.osapublishing.org/abstract.cfm?uri=OTA-2017-OtW2E.1},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping Applications}}}
    }
    

31. In Situ Temperature Control and Measurement with Femtosecond Optical Tweezers: Offering Biomedical Application. D. Mondal and D. Goswami, in Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XV (International Society for Optics and Photonics, 2017), 10068, p. 100681T [Abstract] [PDF] [BibTeX]

    Abstract: We present here the control and measurement of temperature rise using femtosecond optical tweezers at near infrared (NIR) region. Based on our theoretical development, we have designed our experimental techniques. The high temporal sensitivity of position autocorrelation and equipartition theorem is simultaneously applied to elucidate temperature control and high precision measurement around focal volume. Experimentally we have made the benign NIR wavelength to induce local heating by adding very low fluorescent dye molecule with low average power. Local temperature control in aqueous solution exciting within optically absorbing window of the low quantum yield molecules can be possible due to non-radiative relaxation via thermal emission. The stochastic nature of Brownian particle has enough information of its surroundings. We have mapped the nano-dimension beam waist environment by probing the fluctuation of trapped particle. We have observed up to 30K temperature rise from room temperature at sub micro molar concentration. The gradient of temperature is as sharp as the fluence of pulsed laser focused by high numerical aperture objective. Thus, pulsed laser radiation always allows finer surgical techniques involving minimal thermal injuries. Our new techniques with multiphoton absorbing non-fluorescent dye can further be used to selective phototherapeutic diagnosis of cancer cells due to peak power dependent nonlinear phenomenon (NLO).

     BibTeX: @inproceedings{mondalSituTemperatureControl2017,
      title = {In Situ Temperature Control and Measurement with Femtosecond Optical Tweezers: Offering Biomedical Application},
      shorttitle = {In Situ Temperature Control and Measurement with Femtosecond Optical Tweezers},
      booktitle = {Imaging, {{Manipulation}}, and {{Analysis}} of {{Biomolecules}}, {{Cells}}, and {{Tissues XV}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2017-02-16},
      volume = {10068},
      pages = {100681T},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5mrg},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10068/100681T/In-situ-temperature-control-and-measurement-with-femtosecond-optical-tweezers/10.1117/12.2251892.short},
      urldate = {2019-08-01},
      eventtitle = {Imaging, {{Manipulation}}, and {{Analysis}} of {{Biomolecules}}, {{Cells}}, and {{Tissues XV}}}
    }
    

32. Spatiotemporal Control of Energy Transfer in Optically Trapped Systems. D. Mondal, D. Roy, and D. Goswami, in 2015 International Young Scientists Forum on Applied Physics (YSF) (2015), pp. 1–4 [Abstract] [BibTeX]

    Abstract: We demonstrate control over two photon fluorescence (TPF) resonance energy transfer under femtosecond optically tweezed condition. We also extract information about the structure and dynamics of the trapped particles and their clusters as observed from the TPF decay times of the trapped multiple microspheres (0.50 μm size) by varying the polarization of the trapping laser. This micron to nano regime of the energy transfer process has provided us the necessary control over the molecular level energy transfer rate due to the different overlap integral of excitation and emission spectra of the dye that is coated on the surface of 1.0 μm polystyrene particles. Our background free detection method thus provides additional structural information about multiple trapping events.

     BibTeX: @inproceedings{mondalSpatiotemporalControlEnergy2015,
      title = {Spatiotemporal Control of Energy Transfer in Optically Trapped Systems},
      booktitle = {2015 {{International Young Scientists Forum}} on {{Applied Physics}} ({{YSF}})},
      author = {Mondal, D. and Roy, D. and Goswami, D.},
      date = {2015-09},
      pages = {1--4},
      doi = {10/gf5msz},
      eventtitle = {2015 {{International Young Scientists Forum}} on {{Applied Physics}} ({{YSF}})}
    }
    

33. Temperature Control and Measurement with Tunable Femtosecond Optical Tweezers. D. Mondal and D. Goswami, in Optical Trapping and Optical Micromanipulation XIII (International Society for Optics and Photonics, 2016), 9922, p. 992210 [Abstract] [PDF] [BibTeX]

    Abstract: We present the effects of wavelength dependent temperature rise in a femtosecond optical tweezers. Our experiments involve the femtosecond trapping laser tunable from 740-820 nm at low power 25 mW to cause heating in the trapped volume within a homogeneous solution of sub micro-molar concentration of IR dye. The 780 nm high repetition rate laser acts as a resonant excitation source which helps to create the local heating effortlessly within the trapping volume. We have used both position autocorrelation and equipartion theorem to evaluate temperature at different wavelength having different absorption coefficient. Fixing the pulse width in the temporal domain gives constant bandwidth at spatial domain, which makes our system behave as a tunable temperature rise device with high precision. This observation leads us to calculate temperature as well as viscosity within the vicinity of the trapping zone. A mutual energy transfer occurs between the trapped bead and solvents that leads to transfer the thermal energy of solvents into the kinetic energy of the trap bead and vice-versa. Thus hot solvated molecules resulting from resonant and near resonant excitation of trapping wavelength can continuously dissipate heat to the trapped bead which will be reflected on frequency spectrum of Brownian noise exhibited by the bead. Temperature rise near the trapping zone can significantly change the viscosity of the medium. We observe temperature rise profile according to its Gaussian shaped absorption spectrum with different wavelength.

     BibTeX: @inproceedings{mondalTemperatureControlMeasurement2016,
      title = {Temperature Control and Measurement with Tunable Femtosecond Optical Tweezers},
      booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIII}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-09-16},
      volume = {9922},
      pages = {992210},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5mr2},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9922/992210/Temperature-control-and-measurement-with-tunable-femtosecond-optical-tweezers/10.1117/12.2237708.short},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIII}}}
    }
    

34. Thermal Inflection Study of Methanol-Hexane Mixtures Using Time-Resolved Thermal Lens Technique. A. K. Rawat, S. Chakraborty, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–3 [Abstract] [PDF] [BibTeX]

    Abstract: Time-resolved thermal lens (TL) technique is used to measure the heat transfer in pure methanol and its binary mixtures with hexane. We used dual-beam mode mismatched pump-probe scheme where a femtosecond laser beam of 1560 nm was used as a pump beam, and its frequency-doubled 780 nm beam was used as probe beam. TL Signal decreases with increasing concentration of hexane in the binary mixture. On higher concentration of Hexane in binary mixture then we have found convective heat transfer mode was absent. At 40%-60% methanol hexane mixture, we observed a sudden curious jump in TL signal.

     BibTeX: @inproceedings{rawatThermalInflectionStudy2019,
      ids = {rawatThermalInflectionStudy2019a},
      title = {Thermal {{Inflection Study}} of {{Methanol-Hexane Mixtures}} Using {{Time-Resolved Thermal Lens Technique}}},
      booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Rawat, Ashwini Kumar and Chakraborty, Subhajit and Goswami, Debabrata},
      date = {2019-12},
      pages = {1--3},
      issn = {null},
      doi = {10.1109/WRAP47485.2019.9013736},
      url = {10.1109/WRAP47485.2019.9013736},
      eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

35. Polarization Modulated Ultrafast Pulse-Pair Control in Two-Photon Fluorescence Microscopy. D. Roy, A. K. De, and D. Goswami, in Frontiers in Optics 2011/Laser Science XXVII (OSA, 2011), p. JWA3 [Abstract] [PDF] [BibTeX]

    Abstract: Selective fluorescence suppression for two spectrally overlapping fluorophores that undergo simultaneous two-photon absorption from identical femtosecond pulses through precise control in relative timing and polarization of the exciting pulse-pair.

     BibTeX: @inproceedings{royPolarizationModulatedUltrafast2011,
      title = {Polarization Modulated {{Ultrafast Pulse-Pair Control}} in {{Two-Photon Fluorescence Microscopy}}},
      booktitle = {Frontiers in {{Optics}} 2011/{{Laser Science XXVII}}},
      author = {Roy, Debjit and De, Arijit Kumar and Goswami, Debabrata},
      date = {2011},
      pages = {JWA3},
      publisher = {{OSA}},
      location = {{San Jose, California}},
      doi = {10/gf5nqh},
      url = {https://www.osapublishing.org/abstract.cfm?URI=FiO-2011-JWA3},
      urldate = {2019-08-02},
      eventtitle = {Frontiers in {{Optics}}},
      isbn = {978-1-55752-917-6}
    }
    

36. Exploring the Critical Role of Detection Aperture in Thermal Lens Measurements. S. Singhal, I. Bhattacharyya, and D. Goswami, in 2015 Workshop on Recent Advances in Photonics (WRAP) (2015), pp. 1–4 [Abstract] [BibTeX]

    Abstract: The critical role of the detection aperture size on the measurement of thermal lens signals has been explored by using mode-mismatched pump-probe thermal lens spectroscopy in pure methanol. Femtosecond laser pulses at 1560 nm are used to create thermal lens signal, which is simultaneously probed by a collinear 780 nm pulse train through a partially open aperture of different sizes placed after the sample. The trend in the time resolved thermal lens signals reveals that aperture size allowing less than half of the incident probe light is critical in providing accuracy of the thermal lens spectroscopy.

     BibTeX: @inproceedings{singhalExploringCriticalRole2015,
      title = {Exploring the Critical Role of Detection Aperture in Thermal Lens Measurements},
      booktitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Singhal, S. and Bhattacharyya, I. and Goswami, D.},
      date = {2015-12},
      pages = {1--4},
      doi = {10/gf5msd},
      eventtitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

37. Importance of Hydrogen Bonding in Thermal Lens Study of Highly Absorbing Liquids. S. Singhal, P. P. Roy, and D. Goswami, in Frontiers in Optics 2015 (2015), Paper FTu5E.5 (Optical Society of America, 2015), p. FTu5E.5 [Abstract] [PDF] [BibTeX]

    Abstract: Effect of thermal load on highly absorbing hydrogen bonded liquids are explored. We find heat transfer is better facilitated in lesser hydrogen bonded liquids by convection through molecular motion in addition to conduction.

     BibTeX: @inproceedings{singhalImportanceHydrogenBonding2015,
      title = {Importance of {{Hydrogen Bonding}} in {{Thermal Lens Study}} of {{Highly Absorbing Liquids}}},
      booktitle = {Frontiers in {{Optics}} 2015 (2015), Paper {{FTu5E}}.5},
      author = {Singhal, Sumit and Roy, Partha Pratim and Goswami, Debabrata},
      date = {2015-10-18},
      pages = {FTu5E.5},
      publisher = {{Optical Society of America}},
      doi = {10/gf5msf},
      url = {https://www.osapublishing.org/abstract.cfm?uri=FiO-2015-FTu5E.5},
      urldate = {2019-08-01},
      eventtitle = {Frontiers in {{Optics}}}
    }
    

38. Molecular Size and Mass Sensitive Femtosecond Thermal Spectrometer. S. Singhal, S. Goswami, A. Banerjee, and D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (2019), pp. 1–3 [Abstract] [BibTeX]

    Abstract: Though a single ultrashort pulse has inconceivable thermal effect, highly repetitive femtosecond lasers often result in some heating effects. Instead of fretting over the thermal effect, we have used this to develop the time-resolved photothermal lens spectroscopy for molecular sensitivity.

     BibTeX: @inproceedings{singhalMolecularSizeMass2019,
      title = {Molecular {{Size}} and {{Mass Sensitive Femtosecond Thermal Spectrometer}}},
      booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
      author = {Singhal, Sumit and Goswami, Sonaly and Banerjee, A. and Goswami, Debabrata},
      date = {2019-03},
      pages = {1--3},
      doi = {10/gf5mqh},
      eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})}
    }
    

39. Sensitive Dual Beam Thermal Lens Detection of Convection in Methanol. S. Singhal and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. P1A.16 [Abstract] [PDF] [BibTeX]

    Abstract: We show that dual beam mode mismatched thermal lens (TL) technique is more sensitive than the single beam one. Presence of unusual peak inside the dual beam TL signal directly indicates strong convection.

     BibTeX: @inproceedings{singhalSensitiveDualBeam2016,
      title = {Sensitive Dual Beam Thermal Lens Detection of Convection in Methanol},
      booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Singhal, Sumit and Goswami, Debabrata},
      date = {2016},
      pages = {P1A.16},
      publisher = {{OSA}},
      location = {{Kanpur}},
      doi = {10/gf5mrn},
      url = {https://www.osapublishing.org/abstract.cfm?URI=Photonics-2016-P1A.16},
      urldate = {2019-08-01},
      eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
      isbn = {978-1-943580-22-4}
    }
    

40. Study of Starch Using Bright Field and Polarized Light Microscopy. K. K. Singh, Y. Yadav, D. Kumar, A. Singh, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–2 [Abstract] [BibTeX]

    Abstract: Starch is a polymer derived from plants that have various applications. There are various types of starch available like potato, maize, tapioca, and wheat, etc. We have studied and successfully differentiated tapioca and maize starch using polarized light microscopy and bright field techniques with the help of Iodine staining. Starch granules are suspended in aqueous or non-aqueous media for polarized light and bright field microscopy. The botanical source of the starch is identified according to the shape and size of granules, granule surface marking, the position of hilum, iodine staining, and the presence of maltase crosses under polarized light.

     BibTeX: @inproceedings{singhStudyStarchUsing2019,
      title = {Study of {{Starch Using Bright Field}} and {{Polarized Light Microscopy}}},
      booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Singh, Krishna Kant and Yadav, Yogendra and Kumar, Deepak and Singh, Ajitesh and Goswami, Debabrata},
      date = {2019-12},
      pages = {1--2},
      issn = {null},
      doi = {10.1109/WRAP47485.2019.9013741},
      eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

2009-2000

1. Coherent Control in Multiphoton Fluorescence Imaging. A. K. De and D. Goswami, in Multiphoton Microscopy in the Biomedical Sciences IX (International Society for Optics and Photonics, 2009), 7183, p. 71832B [Abstract] [PDF] [BibTeX]

   Abstract: In multiphoton fluorescence laser-scanning microscopy ultrafast laser pulses, i.e. light pulses having pulse-width ≤ 1picosecond (1 ps = 10^-12 s), are commonly used to circumvent the low multiphoton absorption cross-sections of common fluorophores. Starting with a discussion on how amplitude modulation of ultrashort pulse-train enhances the two-photon fluorescence providing deep insight into laser-induced photo-thermal damage, the effect of controlling time lag between phase-locked laser pulses on imaging is described. In addition, the prospects of laser pulse-shaping in signal enhancement (by temporal pulse-compression at the sample) and selective excitation of fluorophores (by manipulating the phase and/or amplitude of different frequency components within the pulse) are discussed with promising future applications lying ahead.

    BibTeX: @inproceedings{deCoherentControlMultiphoton2009,
     title = {Coherent Control in Multiphoton Fluorescence Imaging},
     booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-02-25},
     volume = {7183},
     pages = {71832B},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/d2cztk},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7183/71832B/Coherent-control-in-multiphoton-fluorescence-imaging/10.1117/12.807687.short},
     urldate = {2019-08-14},
     eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}}
   }
   

2. Three-Dimensional Image Formation under Single-Photon Ultra-Short Pulsed Illumination. A. K. De and D. Goswami, in Scanning Microscopy 2009 (International Society for Optics and Photonics, 2009), 7378, p. 737827 [Abstract] [PDF] [BibTeX]

   Abstract: The major thrust of modern day fluorescence laser-scanning microscopy have been towards achieving better and better depth resolution embodied by the invention and subsequent development of confocal and multi-photon microscopic techniques. However, each method bears its own limitations: in having sufficient background fluorescence and photodamage resulting from out-of-focus illumination for the former, while low multi-photon absorption cross-sections of common fluorophores for the latter. Here we show how the intelligent choice of single-photon ultrashort pulsed illumination can circumvent all these shortcomings by exemplifying the tiny spatial stretch of an ultrashort pulse. Besides achieving a novel way of optical sectioning, this new method offers improved signal-to-noise ratio as well as reduced photo-damage which are crucial for live cell imaging under prolonged exposure to light.

    BibTeX: @inproceedings{deThreedimensionalImageFormation2009,
     title = {Three-Dimensional Image Formation under Single-Photon Ultra-Short Pulsed Illumination},
     booktitle = {Scanning {{Microscopy}} 2009},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-05-22},
     volume = {7378},
     pages = {737827},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/b7mtnv},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7378/737827/Three-dimensional-image-formation-under-single-photon-ultra-short-pulsed/10.1117/12.822773.short},
     urldate = {2019-08-14},
     eventtitle = {Scanning {{Microscopy}} 2009}
   }
   

3. Multiphoton Control with Ultrafast Pulse Shaping. D. Goswami and S. A. Hosseini, in Optical Fiber Communication Conference and International Conference on Quantum Information (OSA, 2001), p. PA29 [Abstract] [PDF] [BibTeX]

   Abstract: A multiphoton density-matrix approach explores the effects of ultrafast shaped pulses for two-level systems that do not have a single photon resonance, and show that many multiphoton results are surprisingly similar to the single-photon results. These conditions thus allow extending the single-photon coherent control ideas to develop multiphoton coherent control.

    BibTeX: @inproceedings{goswamiMultiphotonControlUltrafast2001,
     title = {Multiphoton {{Control}} with {{Ultrafast Pulse Shaping}}},
     booktitle = {Optical {{Fiber Communication Conference}} and {{International Conference}} on {{Quantum Information}}},
     author = {Goswami, Debabrata and Hosseini, Syed Abbas},
     date = {2001},
     pages = {PA29},
     publisher = {{OSA}},
     location = {{Rochester, New York}},
     doi = {10/gf6c92},
     url = {https://www.osapublishing.org/abstract.cfm?uri=ICQI-2001-PA29},
     urldate = {2019-08-14},
     eventtitle = {International {{Conference}} on {{Quantum Information}}},
     isbn = {978-1-55752-654-0}
   }
   

4. Nonlinear Optical Response of Carbon Nanotubes Functionalized with a Water Soluble Ink. J. Gupta, given-i=P. C. family=Vijayan given=Prof. C., S. Maurya, and D. Goswami, in (2008) [BibTeX]

    BibTeX: @inproceedings{guptaNonlinearOpticalResponse2008,
     title = {Nonlinear Optical Response of Carbon Nanotubes Functionalized with a Water Soluble Ink},
     author = {Gupta, Jyotsana and family=Vijayan, given=Prof. C., given-i={{Prof}}C and Maurya, Sandeep and Goswami, Debabrata},
     date = {2008-12-01}
   }
   

5. Novel Femtosecond Setup for High Sensitive Absorption Coefficient and Optical Nonlinearities Measurements. S. A. Hosseini, A. Sharan, and D. Goswami, in Nonlinear Optics: Materials, Fundamentals and Applications (2002), Paper MB4 (Optical Society of America, 2002), p. MB4 [Abstract] [PDF] [BibTeX]

   Abstract: We introduce a new method to measure both absorption coefficient and third order optical nonlinearity of materials with high sensitivity in a single experimental setup. A dual-beam pump-probe experiment achieves this goal but shows a counterintuitive coupling.

    BibTeX: @inproceedings{hosseiniNovelFemtosecondSetup2002,
     title = {Novel {{Femtosecond Setup}} for {{High Sensitive Absorption Coefficient}} and {{Optical Nonlinearities Measurements}}},
     booktitle = {Nonlinear {{Optics}}: {{Materials}}, {{Fundamentals}} and {{Applications}} (2002), Paper {{MB4}}},
     author = {Hosseini, S. Abbas and Sharan, A. and Goswami, D.},
     date = {2002-07-29},
     pages = {MB4},
     publisher = {{Optical Society of America}},
     doi = {10/gf6c9t},
     url = {https://www.osapublishing.org/abstract.cfm?uri=NLO-2002-MB4},
     urldate = {2019-08-14},
     eventtitle = {Nonlinear {{Optics}}: {{Materials}}, {{Fundamentals}} and {{Applications}}}
   }
   

6. Time Comb Pulses Through Ultrafast Pulse Shaping. S. K. K. Kumar and D. Goswami, in Controlling Light with Light: Photorefractive Effects, Photosensitivity, Fiber Gratings, Photonic Materials and More (2007), Paper MB61 (Optical Society of America, 2007), p. MB61 [Abstract] [PDF] [BibTeX]

   Abstract: Time-comb of femtosecond pulses at 1560nm is demonstrated by coupling a pulse-shaper in one arm of Mach-Zehnder interferometer. Time comb data for 5-pulses last 80ps. Such pulse-shaping technique is ideal in simultaneous time-wavelength multiplexing and coherent control.

    BibTeX: @inproceedings{kumarTimeCombPulses2007,
     title = {Time {{Comb Pulses Through Ultrafast Pulse Shaping}}},
     booktitle = {Controlling {{Light}} with {{Light}}: {{Photorefractive Effects}}, {{Photosensitivity}}, {{Fiber Gratings}}, {{Photonic Materials}} and {{More}} (2007), Paper {{MB61}}},
     author = {Kumar, S. K. Karthick and Goswami, D.},
     date = {2007-10-14},
     pages = {MB61},
     publisher = {{Optical Society of America}},
     doi = {10/gf6c9f},
     url = {https://www.osapublishing.org/abstract.cfm?uri=PR-2007-MB61},
     urldate = {2019-08-14},
     eventtitle = {Photorefractive {{Effects}}, {{Photosensitivity}}, {{Fiber Gratings}}, {{Photonic Materials}} and {{More}}}
   }
   

7. Nonlinear Optical Properties of Free Standing Films of PbS Quantum Dots in the Nonresonant Femtosecond Regime. P. A. Kurian, C. Vijayan, A. Nag, and D. Goswami, in Z. Gaburro and S. Cabrini, eds. (2007), p. 66390M [Abstract] [PDF] [BibTeX]

   Abstract: Devices based on optical technology for high speed communication networks require materials with large nonlinear optical response in the ultrafast regime. Nonlinear optical materials have also attracted wide attention as potential candidates for the protection of optical sensors and eyes while handling lasers. Optical limiters have a constant transmittance at low input influence and a decrease in transmittance at higher fluences and are based on a variety of mechanisms such as nonlinear refraction, nonlinear scattering, multiphoton absorption and free carrier absorption. As we go from bulk to nanosized materials especially in the strong quantum confinement regime where radius of the nanoparticle is less than the bulk exciton Bohr radius, the optical nonlinearity is enhanced due to quantum confinement effect. This paper is on the ultrafast nonresonant nonlinearity in free standing films of PbS quantum dots stabilized in a synthetic glue matrix by a simple chemical route which provides flexibility of processing in a variety of physical forms. Optical absorption spectrum shows significant blue shift from the bulk absorption onset indicating strong quantum confinement. PbS quantumdots of mean size 3.3nm are characterized by X-ray diffraction and transmission electron microscopy. The mechanism of nonlinear absorption giving rise to optical limiting is probed using open z-scan technique with laser pulses of 150 fs pulse duration at 780 nm and the results are presented in the nonresonant femtosecond regime. Irradiance dependence on nonlinear absorption are discussed.

    BibTeX: @inproceedings{kurianNonlinearOpticalProperties2007,
     title = {Nonlinear Optical Properties of Free Standing Films of {{PbS}} Quantum Dots in the Nonresonant Femtosecond Regime},
     author = {Kurian, Pushpa Ann and Vijayan, C. and Nag, Amit and Goswami, Debabrata},
     editor = {Gaburro, Zeno and Cabrini, Stefano},
     date = {2007-09-13},
     pages = {66390M},
     location = {{San Diego, California, USA}},
     doi = {10/cntz9g},
     url = {http://proceedings.spiedigitallibrary.org/proceeding.aspx?doi=10.1117/12.733034},
     urldate = {2019-08-14},
     eventtitle = {{{NanoScience}} + {{Engineering}}}
   }
   

8. Towards Spatio-Temporal Control in Optical Trapping. D. Roy, A. K. De, and D. Goswami, in Optical Trapping and Optical Micromanipulation VI (International Society for Optics and Photonics, 2009), 7400, p. 74000G [Abstract] [PDF] [BibTeX]

   Abstract: Using both continuous-wave (CW) and high repetition rate femtosecond lasers, we present stable 3-dimensional trapping of 1μm polystyrene microspheres. We also stably trapped 100nm latex nanoparticles using the femtosecond mode-locked laser at a very low average power where the CW lasers cannot trap, demonstrating the significance of the fleeting temporal existence of the femtosecond pulses. Trapping was visualized through dark-field microscopy as well as through a noise free detection using two-photon fluorescence as a diagnostics tool owing to its intrinsic 3- dimensional resolution. Comparison between a Gaussian versus a flat-top Gaussian beam profile demonstrates the importance of laser spatial mode in optical trapping.

    BibTeX: @inproceedings{roySpatiotemporalControlOptical2009,
     title = {Towards Spatio-Temporal Control in Optical Trapping},
     booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VI}}},
     author = {Roy, Debjit and De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-08-20},
     volume = {7400},
     pages = {74000G},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/fpdhxs},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7400/74000G/Towards-spatio-temporal-control-in-optical-trapping/10.1117/12.824372.short},
     urldate = {2019-08-14},
     eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation VI}}}
   }
   

1999-1991

1. Altering Excitation Dynamics in Optically Dense Media Using Shaped Ultrafast Laser Pulses. J. C. Davis, M. R. Fetterman, D. Goswami, Wei Guo Yang, D. Keusters, and W. S. Warren, in Technical Digest. Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference (1999), pp. 107–108 [Abstract] [BibTeX]

   Abstract: Summary form only given. We study the interaction between intense (50 MW peak power), shaped ultrafast laser pulses and optically dense samples of Rb vapor. In particular, we concentrate our attention on laser pulses with a the complex hyperbolic secant envelope, or equivalently, a sech electric field envelope with a tanh frequency sweep. In order to produce and characterize the shaped laser pulses used in our experiments, we exploited several new technologies: amplified, shaped laser pulses were generated using an acousto-optic modulator-based system combined with a chirped-pulse regenerative amplifier. The amplitude and phase of these pulses were then characterized by the STRUT (spectrally and temporally resolved upconversion technique). The STRUT was used to measure the laser pulses both before and after propagating through Rb vapor. Examples of such experimental STRUT images are presented. The complex sech pulse was selected because, in optically thin media, only it and rectangular pulses give complete analytical solutions to the Bloch equations. This shape has been found to generate complete population inversion over a well-defined and amplitude-insensitive bandwidth. In optically dense samples the excited state dynamics are not so straightforward. We have found, both in experiments and theoretically, that the extent and character of the population inversion is related to the frequency sweep of the laser pulses as does the amount of residual excited population after the pulse and any subsequent stimulated emission.

    BibTeX: @inproceedings{davisAlteringExcitationDynamics1999,
     title = {Altering Excitation Dynamics in Optically Dense Media Using Shaped Ultrafast Laser Pulses},
     booktitle = {Technical {{Digest}}. {{Summaries}} of {{Papers Presented}} at the {{Quantum Electronics}} and {{Laser Science Conference}}},
     author = {Davis, J. C. and Fetterman, M. R. and Goswami, D. and {Wei Guo Yang} and Keusters, D. and Warren, W. S.},
     date = {1999-05},
     pages = {107--108},
     doi = {10/cbtw6x},
     eventtitle = {Technical {{Digest}}. {{Summaries}} of {{Papers Presented}} at the {{Quantum Electronics}} and {{Laser Science Conference}}}
   }
   

2. Generation of Amplified Shaped Pulses for Highly Adiabatic Excitation. M. Fetterman, D. Goswami, D. Keusters, J.-K. Rhee, and W. S. Warren, in Ultrafast Phenomena XI, T. Elsaesser, J. G. Fujimoto, D. A. Wiersma, and W. Zinth, eds., Springer Series in Chemical Physics (Springer Berlin Heidelberg, 1998), pp. 24–26 [Abstract] [BibTeX]

   Abstract: Complex amplified pulses, including al ps, 100 µJ tanh-swept sech pulse for adiabatic inversion, are generated experimentally. STRUT detection verifies the modulation and follows the dynamics induced by such pulses in Rb vapor. Applications to production of spin-polarized gases for medical imaging are discussed.

    BibTeX: @inproceedings{fettermanGenerationAmplifiedShaped1998,
     title = {Generation of Amplified Shaped Pulses for Highly Adiabatic Excitation},
     booktitle = {Ultrafast {{Phenomena XI}}},
     author = {Fetterman, Matthew and Goswami, Debabrata and Keusters, Dorine and Rhee, June-Koo and Warren, Warren S.},
     editor = {Elsaesser, Thomas and Fujimoto, James G. and Wiersma, Douwe A. and Zinth, Wolfgang},
     date = {1998},
     series = {Springer {{Series}} in {{Chemical Physics}}},
     pages = {24--26},
     publisher = {{Springer Berlin Heidelberg}},
     isbn = {978-3-642-72289-9}
   }
   

3. Fast and Ultra-Fine Tunable Optical Delay Line at λ = 1.55 Μm Wavelength. W. Yang, D. Keusters, D. Goswami, and W. S. Warren, in (1997) [BibTeX]

    BibTeX: @inproceedings{yangFastUltrafineTunable1997,
     title = {Fast and Ultra-Fine Tunable Optical Delay Line at λ = 1.55 Μm Wavelength},
     author = {Yang, W. and Keusters, D. and Goswami, D. and Warren, W. S.},
     date = {1997-12-15},
     location = {{Princeton University Center for Ultrafast Laser Application}},
     eventtitle = {{{CULA Kick-off Meeting}}}
   }
   

4. Optical-Wavelength-Domain Code Division Multiplexing Using an AOM-based Ultrafast Optical Pulse-Shaping Approach. W. Yang, J. Davis, D. Goswami, M. Fetterman, and W. S. Warren, in All-Optical Networking: Architecture, Control, and Management Issues (International Society for Optics and Photonics, 1998), 3531, pp. 80–86 [Abstract] [PDF] [BibTeX]

   Abstract: Optical wavelength domain code-division multiplexing access (WD-CDMA) using an AOM-based ultrafast optical pulse shaping approach is proposed and demonstrated experimentally at 1550 nm. This new multiplexing technique utilizes wavelength domain codes that are essentially different optical spectral patterns in order to achieve CDMA. In addition to the advantages of the conventional CDMA technique, WD-CDMA can make full use of the entire optical bandwidth without requiring faster optical switches or modulators. This approach also drastically reduces sensitivity to fiber dispersion. Experimentally, we demonstrate an optical spectral encoder using ultrafast optical pulse shaping with 16 wavelength bits over an optical bandwidth of 5 THz. The spectrally-encoded optical pulse generated with the spectral encoder is then decoded with different WD-CDMA codes in the spectral domain. Different code-division channels can thus extract their own bit information while sharing the same spectral-encoded laser pulse as their common carrier. These spectral-encoded pulses are shown using the cross- correlation technique to be confined within a time slot of 15 ps. A larger number of WD bits is also achievable with our system.

    BibTeX: @inproceedings{yangOpticalwavelengthdomainCodeDivision1998,
     title = {Optical-Wavelength-Domain Code Division Multiplexing Using an {{AOM-based}} Ultrafast Optical Pulse-Shaping Approach},
     booktitle = {All-{{Optical Networking}}: {{Architecture}}, {{Control}}, and {{Management Issues}}},
     author = {Yang, Weiguo and Davis, Jennifer and Goswami, Debabrata and Fetterman, Matthew and Warren, Warren S.},
     date = {1998-10-07},
     volume = {3531},
     pages = {80--86},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/chgwnm},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/3531/0000/Optical-wavelength-domain-code-division-multiplexing-using-an-AOM-based/10.1117/12.327047.short},
     urldate = {2019-08-14},
     eventtitle = {All-{{Optical Networking}}: {{Architecture}}, {{Control}}, and {{Management Issues}}}
   }
   

Books and Chapters

2023

1. Chapter 7 - Ultrafast Laser Induced Photothermal Spectroscopy. S. Goswami and D. Goswami, in Photoacoustic and Photothermal Spectroscopy, S. N. Thakur, V. N. Rai, and J. P. Singh, eds. (Elsevier, 2023), pp. 155–184 [Abstract] [PDF] [BibTeX]

   Abstract: Photothermal processes primarily occur in millisecond timescales and are typically not ascribed to femtosecond lasers. However, femtosecond processes that rely on measurements with high repetition rate lasers must contend with cumulative thermal effects, which accumulate ultrafast interaction residuals into millisecond timescales. Consequently, the study of thermal effects with ultrafast lasers galvanized efforts to mitigate the deleterious impact of thermal processes on ultrafast measurements. Remarkably, dissipation dynamics arising from cumulative thermal heating induced by ultrafast lasers are strongly correlated to molecular properties. This correlation has driven the development of ultrafast laser-induced thermal processes for sensitive spectroscopy. We focus on developing the underlying principles of this novel spectroscopic methodology while covering some of its multifaceted applications in this chapter. We pedagogically develop its unique properties compared to other thermal processes, starting from some of the principles of ultrafast lasers and their repetition rates, which are critical in understanding the cumulative thermal load.

    BibTeX: @incollection{goswamiChapterUltrafastLaser2023,
     title = {Chapter 7 - {{Ultrafast}} Laser Induced Photothermal Spectroscopy},
     booktitle = {Photoacoustic and {{Photothermal Spectroscopy}}},
     author = {Goswami, Sonaly and Goswami, Debabrata},
     editor = {Thakur, Surya N. and Rai, Virendra N. and Singh, Jagdish P.},
     date = {2023-01-01},
     pages = {155--184},
     publisher = {{Elsevier}},
     doi = {10.1016/B978-0-323-91732-2.00022-7},
     url = {https://www.sciencedirect.com/science/article/pii/B9780323917322000227},
     urldate = {2023-07-28},
     isbn = {978-0-323-91732-2}
   }
   

2018

1. Solvent Effect on Dual Fluorescence and the Corresponding Excited State Dynamics. D. Goswami, D. K. Das, and K. Makhal, in Reviews in Fluorescence 2017, C. D. Geddes, ed., Reviews in Fluorescence (Springer International Publishing, 2018), pp. 145–160 [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast depopulation dynamics of highly excited states of near-infrared (NIR) tri-carbocyanine dyes is presented in primary alcohols using the femtosecond fluorescence upconversion technique. Pronounced solvent dependence is observed in the dynamics of the highly excited states. Typically, the tri-carbocyanine dyes have strong absorption and fluorescence with a single peak in the NIR region, however, on tuning the excitation wavelength to the visible region, two distinct emission bands are seen with a large peak wavelength difference. Such dual fluorescent peaks correspond to the respective transitions: S2 → S0 for the visible region and S1 → S0 for the NIR region. The exact fluorescent band positions or their intensities strongly depend on the viscosity and polarity of the solvents. The fluorescence decay timescales measured using fluorescence upconversion techniques with femtosecond time resolution also vary significantly as a function of solvent polarity. The faster decay on the ~250 fs and slower decay on the order of picosecond timescale was found which are strongly depending with increasing the chain length of alcohol. Specifically, for example, in the IR144 dye, the faster decay time constant (τ1) increase with the increase in the viscosity and chain length of the alcohol while, in the case of the IR140 dye, we noticed that the τ1 value decreases with increasing viscosity and chain length of alcohols. We invoke the ion-pair formation of IR140 dye with alcohols to explain such behavior.

    BibTeX: @incollection{goswamiSolventEffectDual2018,
     title = {Solvent {{Effect}} on {{Dual Fluorescence}} and the {{Corresponding Excited State Dynamics}}},
     booktitle = {Reviews in {{Fluorescence}} 2017},
     author = {Goswami, Debabrata and Das, Dipak Kumar and Makhal, Krishnandu},
     editor = {Geddes, Chris D.},
     date = {2018},
     series = {Reviews in {{Fluorescence}}},
     pages = {145--160},
     publisher = {{Springer International Publishing}},
     location = {{Cham}},
     doi = {10.1007/978-3-030-01569-5_7},
     url = {https://doi.org/10.1007/978-3-030-01569-5_7},
     urldate = {2019-08-01},
     isbn = {978-3-030-01569-5}
   }
   

2. Femtosecond Laser-Induced Photothermal Effect for Nanoscale Viscometer and Thermometer. D. Mondal, S. Singhal, and D. Goswami, in Selected Topics in Photonics, A. Pradhan and P. K. Krishnamurthy, eds., IITK Directions (Springer Singapore, 2018), pp. 13–17 [Abstract] [PDF] [BibTeX]

   Abstract: A new method of utilizing photothermal effect at nano-volume dimensions to measure viscosity is presented here that can, in turn, provide the surrounding temperature. Our measurements use high repetition rate, low average power, femtosecond laser pulses that induce photothermal effect that is highly influence by the convective mode of heat transfer. This is especially important for absorbing liquids, which is unlike the typical photothermal effects that are due to such ultrashort pulses. Typical thermal processes involve only conductive mode of heat transfer and are phenomenological in nature. Inclusion of convective mode results in additional molecular characteristics of the thermal process. We measure traditional thermal lens with femtosecond pulse train through geometric beam divergence of a collimated laser beam co-propagating with the focused heating laser beam. The refractive index gradient in the sample arising from a focused heating laser creates a thermal lens, which is measured. On the other hand, the same heat gradient from the focusing heating laser beam generates a change in local viscosity in the medium, which changes the trapped stiffness of an optically trapped microsphere in its vicinity. We use co-propagating femtosecond train of laser pulses at 1560 and 780 nm wavelengths for these experiments. We also show from the bulk thermal studies that use of water as sample has the advantage of using conductive mode of heat transfer for femtosecond pulse train excitation.

    BibTeX: @incollection{mondalFemtosecondLaserInducedPhotothermal2018,
     title = {Femtosecond {{Laser-Induced Photothermal Effect}} for {{Nanoscale Viscometer}} and {{Thermometer}}},
     booktitle = {Selected {{Topics}} in {{Photonics}}},
     author = {Mondal, Dipankar and Singhal, Sumit and Goswami, Debabrata},
     editor = {Pradhan, Asima and Krishnamurthy, Pradeep Kumar},
     date = {2018},
     series = {{{IITK Directions}}},
     pages = {13--17},
     publisher = {{Springer Singapore}},
     location = {{Singapore}},
     doi = {10.1007/978-981-10-5010-7_2},
     url = {https://doi.org/10.1007/978-981-10-5010-7_2},
     urldate = {2019-08-01},
     isbn = {978-981-10-5010-7}
   }
   

2014

1. Quantum Distributed Computing Applied to Grover’s Search Algorithm. D. Goswami, in Computing with New Resources: Essays Dedicated to Jozef Gruska on the Occasion of His 80th Birthday, C. S. Calude, R. Freivalds, and I. Kazuo, eds., Lecture Notes in Computer Science (Springer International Publishing, 2014), pp. 192–199 [Abstract] [PDF] [BibTeX]

   Abstract: Grover’s Algorithm finds a unique element in an unsorted stock of NNN-elements in N−−√N\sqrt{N} queries through quantum search. A single-query solution can also be designed, but with an overhead of Nlog2NNlog2⁡NN\log _2 N steps to prepare and post process the query, which is worse than the classical N/2N/2N/2 queries. We show here that by distributing the computing load on a set of quantum computers, we achieve better information theoretic bounds and relaxed space scaling. Howsoever small one quantum computing node is, by virtue of networking and sharing of data, we can virtually work with a sufficiently large qubit space.

    BibTeX: @incollection{goswamiQuantumDistributedComputing2014,
     title = {Quantum {{Distributed Computing Applied}} to {{Grover}}’s {{Search Algorithm}}},
     booktitle = {Computing with {{New Resources}}: {{Essays Dedicated}} to {{Jozef Gruska}} on the {{Occasion}} of {{His}} 80th {{Birthday}}},
     author = {Goswami, Debabrata},
     editor = {Calude, Cristian S. and Freivalds, Rūsiņš and Kazuo, Iwama},
     date = {2014},
     series = {Lecture {{Notes}} in {{Computer Science}}},
     pages = {192--199},
     publisher = {{Springer International Publishing}},
     location = {{Cham}},
     url = {https://my.pcloud.com/publink/show?code=XZMGxr7Zz6GcnHs4eDHBBtjbl9pyEXfvUXhV},
     urldate = {2019-08-02},
     isbn = {978-3-319-13350-8}
   }
   

1. Computing with New Resources: Essays Dedicated to Jozef Gruska on the Occasion of His 80th Birthday. C. S. Calude, R. Freivalds, and I. Kazuo, (Springer, 2014) [Abstract] [BibTeX]

   Abstract: Professor Jozef Gruska is a well known computer scientist for his many and broad results. He was the father of theoretical computer science research in Czechoslovakia and among the first Slovak programmers in the early 1960s. Jozef Gruska introduced the descriptional complexity of grammars, automata, and languages, and is one of the pioneers of parallel (systolic) automata. His other main research interests include parallel systems and automata, as well as quantum information processing, transmission, and cryptography. He is co-founder of four regular series of conferences in informatics and two in quantum information processing and the Founding Chair (1989-96) of the IFIP Specialist Group on Foundations of Computer Science.

    BibTeX: @book{caludeComputingNewResources2014,
     title = {Computing with {{New Resources}}: {{Essays Dedicated}} to {{Jozef Gruska}} on the {{Occasion}} of {{His}} 80th {{Birthday}}},
     shorttitle = {Computing with {{New Resources}}},
     author = {Calude, Cristian S. and Freivalds, Rūsiņš and Kazuo, Iwama},
     date = {2014-12-09},
     eprint = {QLLLBQAAQBAJ},
     eprinttype = {googlebooks},
     publisher = {{Springer}},
     isbn = {978-3-319-13350-8},
     pagetotal = {486}
   }
   

2010

1. Hot Chemistry with Cold Molecules. T. Goswami and D. Goswami, in Laser Pulse Phenomena and Applications (BoD – Books on Demand, 2010), pp. 371–388 [Abstract] [BibTeX]

   Abstract: Pulsed lasers are available in the gas, liquid, and the solid state. These lasers are also enormously versatile in their output characteristics yielding emission from very large energy pulses to very high peak-power pulses. Pulsed lasers are equally versatile in their spectral characteristics. This volume includes an impressive array of current research on pulsed laser phenomena and applications. Laser Pulse Phenomena and Applications covers a wide range of topics from laser powered orbital launchers, and laser rocket engines, to laser-matter interactions, detector and sensor laser technology, laser ablation, and biological applications.

    BibTeX: @incollection{goswamiHotChemistryCold2010,
     title = {Hot {{Chemistry}} with {{Cold Molecules}}},
     booktitle = {Laser {{Pulse Phenomena}} and {{Applications}}},
     author = {Goswami, Tapas and Goswami, Debabrata},
     date = {2010-12-30},
     eprint = {5XSfDwAAQBAJ},
     eprinttype = {googlebooks},
     pages = {371--388},
     publisher = {{BoD – Books on Demand}},
     isbn = {978-953-307-405-4}
   }
   

2008

1. Nano Computing. V. Sahni and D. Goswami, (Tata McGraw-Hill Education, 2008) [Abstract] [BibTeX]

   Abstract: Computing at the nanoscale is set to revolutionize computing and our way of life. Nanocomputing will help technologists to meet the quest to pack power of computing into the smallest possible device without compromising on speed or accuracy. This book will help scientists, researchers and professionals in related disciplines to understand the fundamentals of this upcoming domain.

    BibTeX: @book{sahniNanoComputing2008,
     title = {Nano {{Computing}}},
     author = {Sahni, Vishal and Goswami, Debabrata},
     date = {2008},
     eprint = {2YSWGKtuzzsC},
     eprinttype = {googlebooks},
     publisher = {{Tata McGraw-Hill Education}},
     isbn = {978-0-07-133109-8},
     pagetotal = {193}
   }
   

2007

1. Single Experimental Setup for High Sensitive Absorption Coefficient and Optical Nonlinearities Measurements. D. Goswami, in Lasers and Electro-Optics Research at the Cutting Edge (Nova Publishers, 2007) [Abstract] [BibTeX]

   Abstract: It is expected that ongoing advances in optics will revolutionise the 21st century as they began doing in the last quarter of the 20th. Such fields as communications, materials science, computing and medicine are leaping forward based on developments in optics. This series presents leading edge research on optics and lasers from researchers spanning the globe.

    BibTeX: @incollection{goswamiSingleExperimentalSetup2007,
     title = {Single {{Experimental Setup}} for {{High Sensitive Absorption Coefficient}} and {{Optical Nonlinearities Measurements}}},
     booktitle = {Lasers and {{Electro-optics Research}} at the {{Cutting Edge}}},
     author = {Goswami, Debabrata},
     date = {2007},
     publisher = {{Nova Publishers}},
     isbn = {978-1-60021-194-2}
   }
   

1. Numerical Recipes 3rd Edition: The Art of Scientific Computing. W. H. Press, S. A. Teukolsky, W. T. Vetterling, and B. P. Flannery, (Cambridge University Press, 2007) [Abstract] [BibTeX]

   Abstract: Co-authored by four leading scientists from academia and industry, Numerical Recipes Third Edition starts with basic mathematics and computer science and proceeds to complete, working routines. Widely recognized as the most comprehensive, accessible and practical basis for scientific computing, this new edition incorporates more than 400 Numerical Recipes routines, many of them new or upgraded. The executable C++ code, now printed in color for easy reading, adopts an object-oriented style particularly suited to scientific applications. The whole book is presented in the informal, easy-to-read style that made earlier editions so popular. Please visit www.nr.com or www.cambridge.org/us/numericalrecipes for more details. More information concerning licenses is available at: www.nr.com/licenses New key features: 2 new chapters, 25 new sections, 25% longer than Second Edition Thorough upgrades throughout the text Over 100 completely new routines and upgrades of many more. New Classification and Inference chapter, including Gaussian mixture models, HMMs, hierarchical clustering, Support Vector MachinesNew Computational Geometry chapter covers KD trees, quad- and octrees, Delaunay triangulation, and algorithms for lines, polygons, triangles, and spheres New sections include interior point methods for linear programming, Monte Carlo Markov Chains, spectral and pseudospectral methods for PDEs, and many new statistical distributions An expanded treatment of ODEs with completely new routines Plus comprehensive coverage of linear algebra, interpolation, special functions, random numbers, nonlinear sets of equations, optimization, eigensystems, Fourier methods and wavelets, statistical tests, ODEs and PDEs, integral equations, and inverse theory

    BibTeX: @book{pressNumericalRecipes3rd2007,
     title = {Numerical {{Recipes}} 3rd {{Edition}}: {{The Art}} of {{Scientific Computing}}},
     shorttitle = {Numerical {{Recipes}} 3rd {{Edition}}},
     author = {Press, William H. and Teukolsky, Saul A. and Vetterling, William T. and Flannery, Brian P.},
     date = {2007-09-06},
     eprint = {1aAOdzK3FegC},
     eprinttype = {googlebooks},
     publisher = {{Cambridge University Press}},
     isbn = {978-0-521-88068-8},
     pagetotal = {1195}
   }
   

2006

1. Ultrafast Pulse Shaping Developments for Quantum Computation. S. K. Karthick Kumar and D. Goswami, in Current Topics in Atomic, Molecular and Optical Physics (WORLD SCIENTIFIC, 2006), pp. 133–141 [Abstract] [PDF] [BibTeX]

   Abstract: This paper is geared to provide some logical essence of our work on various aspects quantum computing through optical approach involving the engineering aspects of ultrafast laser pulse modulation and programmability. Such an effort also includes the hunt for an appropriate physical system for quantum information as we present here.

    BibTeX: @incollection{karthickkumarUltrafastPulseShaping2006,
     title = {Ultrafast Pulse Shaping Developments for Quantum Computation},
     booktitle = {Current {{Topics}} in {{Atomic}}, {{Molecular}} and {{Optical Physics}}},
     author = {Karthick Kumar, S. K. and Goswami, Debabrata},
     date = {2006-12-01},
     pages = {133--141},
     publisher = {{WORLD SCIENTIFIC}},
     doi = {10.1142/9789812772510_0010},
     url = {https://www.worldscientific.com/doi/abs/10.1142/9789812772510_0010},
     urldate = {2019-08-14},
     isbn = {978-981-270-379-8},
     volumes = {0}
   }
   

Consolidated List

2023

1. Demonstration of Solute-specific Synergism in Binary Solvents. H. Ali and D. Goswami, Journal of Fluorescence 33(4), 1325–1335 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: The structure and solvation behavior of binary liquid mixtures of Methanol (MeOH) and N, N-Dimethylformamide (DMF) are explored by ascertaining their intermolecular interactions with either Rhodamine-B (RhB) or Rhodamine101 (Rh101) dye through steady-state absorption, emission, and two-photon induced fluorescence. Specifically, in the present investigation, we examine the strong synergistic solvation observed for the combinations of hydrogen bond donating (MeOH) and accepting (DMF) solvent pairs. Solvatochromism causes the solvatochromic probe molecules to sense increased polarity compared to their bulk counterparts. The origin of synergism was explained in terms of solute–solvent and solvent–solvent interactions in binary solvent mixtures interactions, as evidenced by probe dependence. The solvation behavior of the Methanol and DMF binary solvent mixture shows strong probe dependence, with Rh101 showing synergism while RhB does not.

    BibTeX: @article{aliDemonstrationSolutespecificSynergism2023,
     title = {Demonstration of {{Solute-specific Synergism}} in {{Binary Solvents}}},
     author = {Ali, Habib and Goswami, Debabrata},
     date = {2023-07-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {33},
     number = {4},
     pages = {1325--1335},
     issn = {1573-4994},
     doi = {10.1007/s10895-022-03141-8},
     url = {https://doi.org/10.1007/s10895-022-03141-8},
     urldate = {2023-07-28}
   }
   

2. Quality Assessment of the Commercially Available Alcohol-Based Hand Sanitizers with Femtosecond Thermal Lens Spectroscopy. S. Chakraborty, A. K. Rawat, A. K. Mishra, and D. Goswami, PeerJ Analytical Chemistry 5, e25 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: Using femtosecond-pulse-induced thermal lens spectroscopy (FTLS), we report a novel method for the quality measurements of alcohol-based hand sanitizers (ABHS). To sustain its effectiveness, the ABHS must contain the recommended concentration of alcohol content. We diluted the hand sanitizer with water to reduce the quantity of alcohol in the mixture and then performed thermal measurements on it. We performed both dual-beam Z-scan and time-resolved TL measurements to identify the alcoholic content in the ABHS. The thermal lens (TL) signal of the solvent is capable of detecting any relative change in the alcohol content in the mixture. Our technique, therefore, emerges as a sensitive tool for quality testing of alcohol-based hand sanitizers.

    BibTeX: @article{chakrabortyQualityAssessmentCommercially2023,
     title = {Quality Assessment of the Commercially Available Alcohol-Based Hand Sanitizers with Femtosecond Thermal Lens Spectroscopy},
     author = {Chakraborty, Subhajit and Rawat, Ashwini Kumar and Mishra, Amit Kumar and Goswami, Debabrata},
     date = {2023-05-30},
     journaltitle = {PeerJ Analytical Chemistry},
     shortjournal = {PeerJ An. Chem.},
     volume = {5},
     pages = {e25},
     publisher = {{PeerJ Inc.}},
     issn = {2691-6630},
     doi = {10.7717/peerj-achem.25},
     url = {https://peerj.com/articles/achem-25},
     urldate = {2023-07-28}
   }
   

3. Chapter 7 - Ultrafast Laser Induced Photothermal Spectroscopy. S. Goswami and D. Goswami, in Photoacoustic and Photothermal Spectroscopy, S. N. Thakur, V. N. Rai, and J. P. Singh, eds. (Elsevier, 2023), pp. 155–184 [Abstract] [PDF] [BibTeX]

   Abstract: Photothermal processes primarily occur in millisecond timescales and are typically not ascribed to femtosecond lasers. However, femtosecond processes that rely on measurements with high repetition rate lasers must contend with cumulative thermal effects, which accumulate ultrafast interaction residuals into millisecond timescales. Consequently, the study of thermal effects with ultrafast lasers galvanized efforts to mitigate the deleterious impact of thermal processes on ultrafast measurements. Remarkably, dissipation dynamics arising from cumulative thermal heating induced by ultrafast lasers are strongly correlated to molecular properties. This correlation has driven the development of ultrafast laser-induced thermal processes for sensitive spectroscopy. We focus on developing the underlying principles of this novel spectroscopic methodology while covering some of its multifaceted applications in this chapter. We pedagogically develop its unique properties compared to other thermal processes, starting from some of the principles of ultrafast lasers and their repetition rates, which are critical in understanding the cumulative thermal load.

    BibTeX: @incollection{goswamiChapterUltrafastLaser2023,
     title = {Chapter 7 - {{Ultrafast}} Laser Induced Photothermal Spectroscopy},
     booktitle = {Photoacoustic and {{Photothermal Spectroscopy}}},
     author = {Goswami, Sonaly and Goswami, Debabrata},
     editor = {Thakur, Surya N. and Rai, Virendra N. and Singh, Jagdish P.},
     date = {2023-01-01},
     pages = {155--184},
     publisher = {{Elsevier}},
     doi = {10.1016/B978-0-323-91732-2.00022-7},
     url = {https://www.sciencedirect.com/science/article/pii/B9780323917322000227},
     urldate = {2023-07-28},
     isbn = {978-0-323-91732-2}
   }
   

4. Intense Femtosecond Optical Pulse Shaping Approaches to Spatiotemporal Control. D. Goswami, Frontiers in Chemistry 10, (2023) [Abstract] [PDF] [BibTeX]

   Abstract: For studying any event, measurement can never be enough; “control” is required. This means mere passive tracking of the event is insufficient and being able to manipulate it is necessary. To maximize this capability to exert control and manipulate, both spatial and temporal domains need to be jointly accounted for, which has remained an intractable problem at microscopic scales. Simultaneous control of dynamics and position of an observable event requires a holistic combination of spatial and temporal control principles, which gives rise to the field of spatiotemporal control. For this, we present a novel femtosecond pulse-shaping approach. We explain how to achieve spatiotemporal control by spatially manipulating the system through trapping and subsequently or simultaneously exerting temporal control using shaped femtosecond pulses. By leveraging ultrafast femtosecond lasers, the prospect of having temporal control of molecular dynamics increases, and it becomes possible to circumvent the relaxation processes at microscopic timescales. Optical trapping is an exemplary demonstration of spatial control that results in the immobilization of microscopic objects with radiation pressure from a tightly focused laser beam. Conventional single-beam optical tweezers use continuous-wave (CW) lasers for achieving spatial control through photon fluxes, but these lack temporal control knobs. We use a femtosecond high repetition rate (HRR) pulsed laser to bypass this lack of dynamical control in the time domain for optical trapping studies. From a technological viewpoint, the high photon flux requirement of stable optical tweezers necessitates femtosecond pulse shaping at HRR, which has been a barrier until the recent Megahertz pulse shaping developments. Finally, recognizing the theoretical distinction between tweezers with femtosecond pulses and CW lasers is of paramount interest. Non-linear optical (NLO) interactions must be included prima facie to understand pulsed laser tweezers in areas where they excel, like the two-photon-fluorescence-based detection. We show that our theoretical model can holistically address the common drawback of all tweezers. We are able to mitigate the effects of laser-induced heating by balancing this with femtosecond laser-induced NLO effects. An interesting side-product of HRR femtosecond-laser-induced thermal lens is the development of femtosecond thermal lens spectroscopy (FTLS) and its ability to provide sensitive molecular detection.

    BibTeX: @article{goswamiIntenseFemtosecondOptical2023,
     title = {Intense Femtosecond Optical Pulse Shaping Approaches to Spatiotemporal Control},
     author = {Goswami, Debabrata},
     date = {2023},
     journaltitle = {Frontiers in Chemistry},
     volume = {10},
     issn = {2296-2646},
     url = {https://www.frontiersin.org/articles/10.3389/fchem.2022.1006637},
     urldate = {2023-07-28}
   }
   

5. Unified Software Design Patterns for Simulated Annealing. R. Goswami, R. S., A. Goswami, S. Goswami, and D. Goswami, (2023) [Abstract] [PDF] [BibTeX]

   Abstract: Any optimization alogrithm programming interface can be seen as a black-box function with additional free parameters. In this spirit, simulated annealing (SA) can be implemented in pseudo-code within the dimensions of single slide with free parameters relating to the annealing schedule. Such an implementation however, neglects necessarily much of the structure necessary to take advantage of advances in computing resources, and algorithmic breakthroughs. Simulated annealing is often introduced in myriad disciplines, from discrete examples like the Traveling Salesman Problem (TSP) to molecular cluster potential energy exploration or even explorations of a protein’s configurational space. Theoretical guarantees also demand a stricter structure in terms of statistical quantities, which cannot simply be left to the user. We will introduce several standard paradigms and demonstrate how these can be "lifted" into a unified framework using object oriented programming in Python. We demonstrate how clean, interoperable, reproducible programming libraries can be used to access and rapidly iterate on variants of Simulated Annealing in a manner which can be extended to serve as a best practices blueprint or design pattern for a data-driven optimization library.

    BibTeX: @online{goswamiUnifiedSoftwareDesign2023,
     title = {Unified {{Software Design Patterns}} for {{Simulated Annealing}}},
     author = {Goswami, Rohit and S., Ruhila and Goswami, Amrita and Goswami, Sonaly and Goswami, Debabrata},
     date = {2023-02-06},
     eprint = {2302.02811},
     eprinttype = {arxiv},
     eprintclass = {physics},
     url = {http://arxiv.org/abs/2302.02811},
     urldate = {2023-02-10},
     pubstate = {preprint}
   }
   

6. Exploring the Effects of Intermolecular Interactions on the Self-Defocusing of Binary Liquid Mixtures Using Single Beam z-Scan Technique - Asian Journal of Physics. R. K. Gupta, S. Kant, and D. Goswami, Asian Journal of Physics 31, 897–904 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: Self-defocusing (or negative lens effect) study of different sets of binary liquid mixtures having varying polarities has been carried out by employing a high repetition rate (HRR) femtosecond pulsed laser and utilising a single beam close aperture z-scan (CAZS) technique. We determined the change in transmittance values between peak and valley (ΔTp-v) of the CAZS trace for each different binary liquid mixtures at the varying composition of components. We correlated the variation of ΔTp-v values with the composition ratio of components to the change in physical parameters, which in turn affects the intermolecular interactions. Here, the combined effects of polarity differences and different molecular structures having steric hindrance are found to affect intermolecular interactions significantly in binary mixtures which in turn affect the self-defocusing effect.

    BibTeX: @article{guptaExploringEffectsIntermolecular2023,
     title = {Exploring the Effects of Intermolecular Interactions on the Self-Defocusing of Binary Liquid Mixtures Using Single Beam z-Scan Technique - {{Asian Journal}} of {{Physics}}},
     author = {Gupta, Rahul K. and Kant, Surya and Goswami, Debabrata},
     date = {2023-02-20},
     journaltitle = {Asian Journal of Physics},
     volume = {31},
     pages = {897--904},
     url = {https://asianjournalofphysics.com/exploring-the-effects-of-intermolecular-interactions-on-the-self-defocusing-of-binary-liquid-mixtures-using-single-beam-z-scan-technique/},
     urldate = {2023-07-28}
   }
   

7. Quantifying Coherence with Principal Diagonal Elements of Density Matrix. M. Hazra and D. Goswami, (2023) [Abstract] [PDF] [BibTeX]

   Abstract: Being the key resource in quantum physics, the proper quantification of coherence is of utmost importance. Amid complex-looking functionals in quantifying coherence, we set forth a simple and easy-to-evaluate approach: Principal diagonal difference of coherence (C_PDD), which we prove to be non-negative, self-normalized, and monotonic (under any incoherent operation). To validate this theory, we thought of a fictitious two-qubit system (both interacting and non-interacting) and, through the laser pulse-system interaction (semi-classical approach), compare the coherence evolution of C_PDD with the relative entropy of coherence (C_(r.e)) and l_1-norm of coherence (C_(l_1 )), in a pure-state regime. The numerical results show that the response of C_PDD is better than the other two quantifiers. To the best of our knowledge, this letter is the first to show that a set of density-matrix diagonal elements carries complete information on the coherence (or superposition) of any pure quantum state.

    BibTeX: @online{hazraQuantifyingCoherencePrincipal2023,
     title = {Quantifying Coherence with Principal Diagonal Elements of Density Matrix},
     author = {Hazra, Manis and Goswami, Debabrata},
     date = {2023-02-06},
     eprint = {2301.12295},
     eprinttype = {arxiv},
     eprintclass = {quant-ph},
     doi = {10.48550/arXiv.2301.12295},
     url = {http://arxiv.org/abs/2301.12295},
     urldate = {2023-07-28},
     pubstate = {preprint}
   }
   

8. Investigating the pH Dependence of Thermal Signatures in Monohydric and Polyhydric Alcohols Using Time-Resolved Thermal Lens Spectroscopy. A. K. Rawat, S. Chakraborty, A. K. Mishra, and D. Goswami, Optical Materials 137, 113623 (2023) [Abstract] [PDF] [BibTeX]

   Abstract: We study the influence of pH on the thermophysical properties of monohydric and polyhydric alcohols through a femtosecond laser-induced thermal lens (TL) spectroscopic technique. Relative changes in the thermal signatures of monohydric and polyhydric alcohols are identified at different pH levels using both dual-beam Z-scan and time-resolved TL measurements. We found the TL signatures of the alcohols not to be affected in the acidic region, but a significant change is noticed in the alkaline environment. It is observed that in an alkaline environment (pH > 7), the TL signal significantly increases for short-chain (MeOH and EtOH) monohydric alcohols. In contrast, the TL signal for longer chain length monohydric alcohols (HxOH and phenol) and polyhydroxy alcohols (Ethylene glycol & Glycerol) fall enormously. These results depend strongly on the molecular characteristics of solvents and their interaction strength with the solute as a function of changing pH strength. Our results show the influence of pH on the natural drifting and the heat dissipation characteristics of solvent molecules, which prominently participate in changing the TL signatures of samples. This event could be attributed to changes in molecular arrangements by developing solvation shells (through ions-solvents interactions) in the systems. We investigate the influence of various factors, namely, chain length, structure, polarity, and inter or the intra-H-bonding ability of solvent molecules and ion concentration, which effectively alter the solute-solvent interaction strengths at different pH values (especially in an alkaline environment). The findings through our TL measurements explore this event in great detail for the first time. We try to correlate the molecular characteristics and its ions-solvent interaction effects with the thermophysical properties of alcohols.

    BibTeX: @article{rawatInvestigatingPHDependence2023,
     title = {Investigating the {{pH}} Dependence of Thermal Signatures in Monohydric and Polyhydric Alcohols Using Time-Resolved Thermal Lens Spectroscopy},
     author = {Rawat, Ashwini Kumar and Chakraborty, Subhajit and Mishra, Amit Kumar and Goswami, Debabrata},
     date = {2023-03-01},
     journaltitle = {Optical Materials},
     shortjournal = {Optical Materials},
     volume = {137},
     pages = {113623},
     issn = {0925-3467},
     doi = {10.1016/j.optmat.2023.113623},
     url = {https://www.sciencedirect.com/science/article/pii/S0925346723001957},
     urldate = {2023-07-28}
   }
   

2022

1. Electron Transfer, Spectroscopy and Theory: General Discussion. A. Anilkumar, P. Ash, A. R. Chakravarty, P. Comba, S. DeBeer, A. Dey, A. Draksharapu, D. Goswami, S. Itoh, K. Karlin, K. V. Lakshmi, S. Mazumdar, D. Pantazis, D. Parker, L. Que, G. Rajaraman, S. Prasad Rath, C. Sastri, S. S. Gupta, and E. I. Solomon, Faraday Discussions 234(0), 245–263 (2022) [PDF] [BibTeX]

    BibTeX: @article{anilkumarElectronTransferSpectroscopy2022,
     title = {Electron Transfer, Spectroscopy and Theory: General Discussion},
     shorttitle = {Electron Transfer, Spectroscopy and Theory},
     author = {Anilkumar, Anjali and Ash, Philip and R.~Chakravarty, Akhil and Comba, Peter and DeBeer, Serena and Dey, Abhishek and Draksharapu, Apparao and Goswami, Debabrata and Itoh, Shinobu and Karlin, Kenneth and V.~Lakshmi, K. and Mazumdar, Shyamalava and Pantazis, Dimitrios and Parker, David and Que, Lawrence and Rajaraman, Gopalan and Prasad~Rath, Sankar and Sastri, Chivukula and Gupta, Sayam Sen and I.~Solomon, Edward},
     date = {2022},
     journaltitle = {Faraday Discussions},
     volume = {234},
     number = {0},
     pages = {245--263},
     publisher = {{Royal Society of Chemistry}},
     doi = {10.1039/D2FD90013K},
     url = {https://pubs.rsc.org/en/content/articlelanding/2022/fd/d2fd90013k},
     urldate = {2022-12-31}
   }
   

2. Natural and Artificial Enzymes and Medicinal Aspects: General Discussion. P. Ash, A. R. Chakravarty, P. Comba, A. Dey, D. Goswami, C. Martin Jäger, K. Karlin, S. Kundu, S. L. Gatta, R. L. Domene, J.-D. Maréchal, S. Mazumdar, G. Mugesh, D. Pantazis, A. Pordea, P. J. Sadler, V. Schünemann, S. S. Gupta, O. Shoji, E. I. Solomon, P. Walton, and J. A. Wolny, Faraday Discussions 234(0), 367–387 (2022) [PDF] [BibTeX]

    BibTeX: @article{ashNaturalArtificialEnzymes2022,
     title = {Natural and Artificial Enzymes and Medicinal Aspects: General Discussion},
     shorttitle = {Natural and Artificial Enzymes and Medicinal Aspects},
     author = {Ash, Philip and R.~Chakravarty, Akhil and Comba, Peter and Dey, Abhishek and Goswami, Debabrata and Martin~Jäger, Christof and Karlin, Kenneth and Kundu, Subrata and Gatta, Salvatore La and Domene, Rocío López and Maréchal, Jean-Didier and Mazumdar, Shyamalava and Mugesh, Govindasamy and Pantazis, Dimitrios and Pordea, Anca and J.~Sadler, Peter and Schünemann, Volker and Gupta, Sayam Sen and Shoji, Osami and I.~Solomon, Edward and Walton, Paul and A.~Wolny, Juliusz},
     date = {2022},
     journaltitle = {Faraday Discussions},
     volume = {234},
     number = {0},
     pages = {367--387},
     publisher = {{Royal Society of Chemistry}},
     doi = {10.1039/D2FD90014A},
     url = {https://pubs.rsc.org/en/content/articlelanding/2022/fd/d2fd90014a},
     urldate = {2022-12-31}
   }
   

3. Sensing Non-Ideal Microheterogeneity in Binary Mixtures of Dimethyl Sulfoxide and Water. S. N. Bandyopadhyay, A. Singh, K. K. Singh, and D. Goswami, Journal of Optics 24(5), 054001 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: We present a microscopic study of water–dimethyl sulfoxide (DMSO) binary mixtures using optical tweezers and thermal lens techniques. Binary mixtures of DMSO with water show anomalous behavior due to the specific hydrogen bonding ability of DMSO. We use a tightly focused femtosecond laser at a low average power to optically trap microspheres with diameters of 1 micron for use as probes. The binary mixture exhibits various viscosities, depending on its composition ratio, and hence different trapped particle characteristic frequencies (corner frequencies) due to Brownian motion. The power spectrum density method is used to obtain the corner frequency from forward-scattered data. Thus, using low-power optical tweezer experiments, we find that the maximum viscosity occurs at a DMSO mole fraction of 0.276. At higher powers, the propensity for trapping is highly diminished. It may be surprising to note that these viscosity values obtained from the corner frequencies do not exactly match those published in the literature. However, this deviation can be attributed to the thermal behavior of the binary mixture, which affects the Brownian motion and hence the obtained viscosity values. Studies at the microscopic level can thus provide a newer perspective on these already important binary mixtures. Intensity-dependent measurements further confirm the contribution of thermal effects in this study.

    BibTeX: @article{bandyopadhyaySensingNonidealMicroheterogeneity2022,
     title = {Sensing Non-Ideal Microheterogeneity in Binary Mixtures of Dimethyl Sulfoxide and Water},
     author = {Bandyopadhyay, Soumendra Nath and Singh, Ajitesh and Singh, Krishna Kant and Goswami, Debabrata},
     date = {2022-05-01},
     journaltitle = {Journal of Optics},
     shortjournal = {J. Opt.},
     volume = {24},
     number = {5},
     pages = {054001},
     issn = {2040-8978, 2040-8986},
     doi = {10.1088/2040-8986/ac50ff},
     url = {https://iopscience.iop.org/article/10.1088/2040-8986/ac50ff},
     urldate = {2022-12-31}
   }
   

4. Diluting Convective Effects in Femtosecond Laser Induced Thermal Lens Measurements with Thermally Active Constituents. S. Chakraborty, A. K. Mishra, A. K. Rawat, and D. Goswami, in Frontiers in Optics + Laser Science 2022 (FIO, LS) (2022), Paper JW5A.25 (Optica Publishing Group, 2022), p. JW5A.25 [Abstract] [PDF] [BibTeX]

   Abstract: We report Thermal Lens measurements on the binary liquid mixtures of Methanol and Phenol with femtosecond pulse excitations. The photothermal response is found to be strongly dependent on relative concentrations and the constituents’ molecular properties.

    BibTeX: @inproceedings{chakrabortyDilutingConvectiveEffects2022,
     title = {Diluting {{Convective Effects}} in {{Femtosecond Laser Induced Thermal Lens Measurements}} with {{Thermally Active Constituents}}},
     booktitle = {Frontiers in {{Optics}} + {{Laser Science}} 2022 ({{FIO}}, {{LS}}) (2022), Paper {{JW5A}}.25},
     author = {Chakraborty, Subhajit and Mishra, Amit Kumar and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2022-10-17},
     pages = {JW5A.25},
     publisher = {{Optica Publishing Group}},
     url = {https://opg.optica.org/abstract.cfm?uri=FiO-2022-JW5A.25},
     urldate = {2022-12-31},
     eventtitle = {Frontiers in {{Optics}}}
   }
   

5. An Investigation of Evanescent Wave-Induced Fluorescence Spectroscopy for Exploring High Refractive Index Media. S. Chakraborty, Y. Xu, A. Roberts, D. Goswami, and T. A. Smith, Physica Scripta 98(1), 015014 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Evanescent wave-induced fluorescence spectroscopy (EWIFS) is a widely used technique for probing the interfacial behavior of different complex media in investigations of samples in the physical, chemical, and biological sciences. This technique takes advantage of the sharply decaying evanescent field, established following total internal reflection (TIR) at the interface of two media, for spatially identifying the photoluminescence characteristics of the sample. The generation of the evanescent field requires the refractive index of the second medium to be lower than that of the first, so a major disadvantage of this increasingly widely used spectroscopic technique is the inability to exploit the advantages of EWIFS to image a sample with a higher refractive index than the incident substrate medium. A proposed configuration in which a thin, low refractive index intermediate layer is established between the TIR substrate and a high refractive index sample is investigated. We illustrate that this arrangement does not afford the desired advantages of evanescent field-induced fluorescence measurements for investigating high refractive index media.

    BibTeX: @article{chakrabortyInvestigationEvanescentWaveinduced2022,
     title = {An Investigation of Evanescent Wave-Induced Fluorescence Spectroscopy for Exploring High Refractive Index Media},
     author = {Chakraborty, Subhajit and Xu, Yang and Roberts, Ann and Goswami, Debabrata and Smith, Trevor A.},
     date = {2022-12},
     journaltitle = {Physica Scripta},
     shortjournal = {Phys. Scr.},
     volume = {98},
     number = {1},
     pages = {015014},
     publisher = {{IOP Publishing}},
     issn = {1402-4896},
     doi = {10.1088/1402-4896/aca437},
     url = {https://dx.doi.org/10.1088/1402-4896/aca437},
     urldate = {2022-12-31}
   }
   

6. Probing Solvent Dependent Femtosecond Transient Coherent Oscillations to Reveal Interfacial Dynamics. D. K. Das, K. Makhal, and D. Goswami, Journal of Optics 24(6), 063001 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Probing transient states in molecules having vibronic transitions with femtosecond (fs) laser pulses often results in coherent oscillations either in the ground state, the excited states, or both. We find such coherent oscillations are highly solvent-dependent and provide a holistic overview of the pump-probe experiments for ultrafast dye dynamics at interfaces. For molecules dissolved in single solvents, modulations in oscillations occur due to transitions in the sub-vibrational levels of the electronic state. For binary solvents, in particular, these modulations are strongly sensitive to solvent compositions. The changes induced by various solvent compositions are drastic enough to act as a control parameter for dynamical control processes. We demonstrate an end-to-end understanding of ground-state coherent oscillations, vibrational cooling, ground-state recovery processes, and excited-state dynamics through a series of experiments. We further present a methodology for establishing such control using near-infrared dyes to measure the oscillations with fs pump-probe techniques. In the case of immiscible binary solvents, the same method allows us to investigate the liquid–liquid interface. Our control methodology is validated by an experiment using a cyanine dye dissolved in dimethyl sulfoxide, interfaced with neat diethyl-ether. The dye dynamics are retarded on moving from the bulk dye solution towards the interface with the neat diethyl-ether. When sampled along the direction of the vector pointing from the bulk towards the near interface, monotonically decreasing time constants are obtained. This result strongly suggests the importance of microheterogeneity in interfacial dynamics.

    BibTeX: @article{dasProbingSolventDependent2022,
     title = {Probing Solvent Dependent Femtosecond Transient Coherent Oscillations to Reveal Interfacial Dynamics},
     author = {Das, D. K. and Makhal, K. and Goswami, Debabrata},
     date = {2022-05},
     journaltitle = {Journal of Optics},
     shortjournal = {J. Opt.},
     volume = {24},
     number = {6},
     pages = {063001},
     publisher = {{IOP Publishing}},
     issn = {2040-8986},
     doi = {10.1088/2040-8986/ac675b},
     url = {https://dx.doi.org/10.1088/2040-8986/ac675b},
     urldate = {2022-12-31}
   }
   

7. Interplay of Thermal and Nonlinear Processes for Stable Optical Tweezers. D. Goswami, in Optical Trapping and Optical Micromanipulation XIX (SPIE, 2022), 12198, pp. 82–89 [Abstract] [PDF] [BibTeX]

   Abstract: Single-beam optical tweezers that use continuous wave (CW) lasers for trapping microscopic particles can be understood in terms of force-balancing light pressure from a tightly focused laser beam. High-repetition-rate femtosecond lasers for single-beam optical trapping research have matured as a technique and have garnered increasing interest. There are important differences between the theoretical models for femtosecond laser tweezers and the CW tweezers, e.g., in the sensitive detection of background-free two-photon fluorescence. The instantaneous trapping potential is due to the high peak power of each laser pulse, while the sustained stable trapping regime is a consequence of the high repetition rate of successive pulses. Simulating real-time scenarios for predicting optical trapping behavior continues to be a challenging problem. However, the capability and usefulness of optical tweezers setups with both CW and pulsed lasers are well established. For a tightly focused beam as used in an optical tweezer, cumulative heating can occur despite the minimal absorption cross-section of the trapping medium or the trapped particle, which reaches its maximum value near the focus. A temperature gradient from the laser focal spot is thus generated outwards from the laser focus in the medium, creating a refractive index gradient across the focusing region. The refractive index attains its minimum value at the focus, gradually increasing as a function of increasing distance from it. Since the trapping force and potential depend on the refractive index of the medium, the thermal effect impacts the force and potential of the trapped particle significantly. With CW lasers, computational evidence of temperature rise at the focus of optical tweezers has been posited, which, unfortunately, is not a feasible approach for ultrafast lasers, given their inherent computational complexities. A better understanding of high photon-flux induced processes and a working model of the single-beam optical tweezers that could address both CW and pulsed lasers would be ideal for elucidating the effects of this inherent thermal gradient of the optical tweezers. We demonstrate a framework that includes all possible nonlinear effects arising from high photon flux interactions and validate this with experimental results. Our approach allows a coherent and consistent treatment for both CW and ultrafast cases. We have the purely thermal nonlinear effects for the CW laser case, while for the ultrafast laser case, we include both the thermal and the Kerr type nonlinearities. Such a source-sensitive model is amenable to high throughput computations when coupled with a suitable paradigm for modeling experimental conditions as well.

    BibTeX: @inproceedings{goswamiInterplayThermalNonlinear2022,
     title = {Interplay of Thermal and Nonlinear Processes for Stable Optical Tweezers},
     booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIX}}},
     author = {Goswami, Debabrata},
     date = {2022-10-03},
     volume = {12198},
     pages = {82--89},
     publisher = {{SPIE}},
     doi = {10.1117/12.2633345},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/12198/121980D/Interplay-of-thermal-and-nonlinear-processes-for-stable-optical-tweezers/10.1117/12.2633345.full},
     urldate = {2022-12-31},
     eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIX}}}
   }
   

8. Reproducible High Performance Computing without Redundancy with Nix. R. Goswami, R. S., A. Goswami, S. Goswami, and D. Goswami, in 2022 Seventh International Conference on Parallel, Distributed and Grid Computing (PDGC) (2022), pp. 238–242 [Abstract] [BibTeX]

   Abstract: High performance computing (HPC) clusters are typically managed in a restrictive manner; the large user base makes cluster administrators unwilling to allow privilege escalation. Here we discuss existing methods of package management, including those which have been developed with scalability in mind, and enumerate the drawbacks and advantages of each management methodology. We contrast the paradigms of containerization via docker, virtualization via KVM, pod-infrastructures via Kubernetes, and specialized HPC packaging systems via Spack and identify key areas of neglect. We demonstrate how functional programming due to reliance on immutable states has been leveraged for deterministic package management via the nix-language expressions. We show its associated ecosystem is a prime candidate for HPC package management. We further develop guidelines and identify bottlenecks in the existing structure and present the methodology by which the nix ecosystem should be developed further as an optimal tool for HPC package management. We assert that the caveats of the nix ecosystem can easily mitigated by considerations relevant only to HPC systems, without compromising on functional methodology and features of the nix-language. We show that benefits of adoption in terms of generating reproducible derivations in a secure manner allow for workflows to be scaled across heterogeneous clusters. In particular, from the implementation hurdles faced during the compilation and running of the d-SEAMS scientific software engine, distributed as a nix-derivation on an HPC cluster, we identify communication protocols for working with SLURM and TORQUE user resource allocation queues. These protocols are heuristically defined and described in terms of the reference implementation required for queue-efficient nix builds.

    BibTeX: @inproceedings{goswamiReproducibleHighPerformance2022,
     title = {Reproducible {{High Performance Computing}} without {{Redundancy}} with {{Nix}}},
     booktitle = {2022 {{Seventh International Conference}} on {{Parallel}}, {{Distributed}} and {{Grid Computing}} ({{PDGC}})},
     author = {Goswami, Rohit and S., Ruhila and Goswami, Amrita and Goswami, Sonaly and Goswami, Debabrata},
     date = {2022-11},
     pages = {238--242},
     issn = {2573-3079},
     doi = {10.1109/PDGC56933.2022.10053342},
     eventtitle = {2022 {{Seventh International Conference}} on {{Parallel}}, {{Distributed}} and {{Grid Computing}} ({{PDGC}})}
   }
   

9. Investigating the Effects of Intermolecular Interactions on Nonlinear Optical Properties of Binary Mixtures with High Repetition Rate Femtosecond Laser Pulses. R. K. Gupta, S. Verma, S. Singhal, S. Kant, and D. Goswami, PeerJ Physical Chemistry 4, e23 (2022) [Abstract] [PDF] [BibTeX]

   Abstract: Measurements of nonlinear optical (NLO) properties of different binary mixtures having carbon disulfide (CS2) as the common component, namely CS2-acetone, CS2-cyclopentanone, CS2-toluene, and CS2-carbon tetrachloride (CCl4), are carried out by using the z-scan technique. Open-aperture z-scan (OAZS) and close-aperture z-scan (CAZS) experiments are performed to determine the nonlinear absorption coefficient (β) and nonlinear refractive index (n2) of all binary liquid mixtures at various compositions of the components by employing a pulsed, high repetition rate (HRR) femtosecond laser. Also, we were able to use the flowing liquid to measure NLO properties in the CS2-acetone binary mixture to remove the cumulative thermal effects produced due to the pulsed HRR laser light. Nonlinear refractive index (n2) values are found to be influenced by the weak dipole-induced dipole intermolecular interactions between the nonpolar CS2 and polar acetone as well as cyclopentanone of the respective binary mixtures. On the contrary n2 values are not found to be affected by the intermolecular interactions in CS2-toluene and CS2-CCl4 binary mixtures. In comparison, the nonlinear absorption coefficient (β) values are not found to be affected by the same in all different sets of binary mixtures.

    BibTeX: @article{guptaInvestigatingEffectsIntermolecular2022,
     title = {Investigating the Effects of Intermolecular Interactions on Nonlinear Optical Properties of Binary Mixtures with High Repetition Rate Femtosecond Laser Pulses},
     author = {Gupta, Rahul Kumar and Verma, Sachin and Singhal, Sumit and Kant, Surya and Goswami, Debabrata},
     date = {2022-06-07},
     journaltitle = {PeerJ Physical Chemistry},
     shortjournal = {PeerJ Phy. Chem.},
     volume = {4},
     pages = {e23},
     publisher = {{PeerJ Inc.}},
     issn = {2689-7733},
     doi = {10.7717/peerj-pchem.23},
     url = {https://peerj.com/articles/pchem-23},
     urldate = {2022-12-31}
   }
   

10. Modification of the Expression of L1-Norm of Coherence. M. Hazra and D. Goswami, in Quantum 2.0 Conference and Exhibition (2022), Paper QW2A.3 (Optica Publishing Group, 2022), p. QW2A.3 [Abstract] [PDF] [BibTeX]

    Abstract: Though a well-verified approach of quantifying quantum coherence is l1-norm, this is not normalized for a multi-qubit (multi-level) system. We propose a modification to show that the altered expression normalizes a multi-qubit (multi-level) system coherence with numerical studies.

     BibTeX: @inproceedings{hazraModificationExpressionL1norm2022,
      title = {Modification of the Expression of L1-Norm of Coherence},
      booktitle = {Quantum 2.0 {{Conference}} and {{Exhibition}} (2022), Paper {{QW2A}}.3},
      author = {Hazra, Manis and Goswami, Debabrata},
      date = {2022-06-13},
      pages = {QW2A.3},
      publisher = {{Optica Publishing Group}},
      doi = {10.1364/QUANTUM.2022.QW2A.3},
      url = {https://opg.optica.org/abstract.cfm?uri=QUANTUM-2022-QW2A.3},
      urldate = {2022-12-31},
      eventtitle = {Quantum 2.0}
    }
    

11. Achieving Molecular Distinction in Alcohols with Femtosecond Thermal Lens Spectroscopy. A. Kumar Rawat, S. Chakraborty, A. Kumar Mishra, and D. Goswami, Chemical Physics 561, 111596 (2022) [Abstract] [PDF] [BibTeX]

    Abstract: Using thermal lens (TL) spectroscopy, we distinguish monohydric alcohols based on their molecular characteristics and thermophysical properties. We use both dual-beam Z-scan and time-resolved TL measurements to identify thermal signatures of the representative homologous series of aliphatic, cyclic, and aromatic alcohols. While, in aliphatic alcohols, TL signal amplitude depends strongly on the molecular size and chain length; for cyclic and aromatic alcohols, their photophysical characteristics exhibit dominance over the molecular influence of TL signal. The convective properties of short-chain molecules result in a characteristic trend in dual-beam experiments. Methanol displays the lowest steady-state TL signal due to its fast diffusive capabilities. At the same time, phenol shows the most prominent steady-state TL signal owing to its strong H-bonded cluster formation ability through resonant structures. TL measurements successfully distinguish alcohols belonging to the respective homologous series and additionally discern solvents with a similar number of carbon atoms belonging to different homologous series.

     BibTeX: @article{kumarrawatAchievingMolecularDistinction2022,
      title = {Achieving Molecular Distinction in Alcohols with Femtosecond Thermal Lens Spectroscopy},
      author = {Kumar Rawat, Ashwini and Chakraborty, Subhajit and Kumar Mishra, Amit and Goswami, Debabrata},
      date = {2022-09-01},
      journaltitle = {Chemical Physics},
      shortjournal = {Chemical Physics},
      volume = {561},
      pages = {111596},
      issn = {0301-0104},
      doi = {10.1016/j.chemphys.2022.111596},
      url = {https://www.sciencedirect.com/science/article/pii/S0301010422001513},
      urldate = {2022-12-31}
    }
    

12. Poly-Lysinated Nanoscale Carbon Probe for Low Power Two-Photon Bioimaging. S. Kundu, N. Chatterjee, S. Chakraborty, A. Gupta, D. Goswami, and S. K. Misra, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 270, 120778 (2022) [BibTeX]

     BibTeX: @article{kunduPolylysinatedNanoscaleCarbon2022,
      title = {Poly-Lysinated Nanoscale Carbon Probe for Low Power Two-Photon Bioimaging},
      author = {Kundu, Sayan and Chatterjee, Niranjan and Chakraborty, Subhajit and Gupta, Arjit and Goswami, Debabrata and Misra, Santosh K.},
      date = {2022},
      journaltitle = {Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy},
      volume = {270},
      pages = {120778},
      publisher = {{Elsevier}}
    }
    

13. ‪Control of Selective Two-Photon Fluorescence Suppression by One-Color Pulse-Pair Excitation‬. D. Roy, A. K. De, and D. Goswami, Asian Journal of Physics 31(3-5), 475–478 (2022) [Abstract] [PDF] [BibTeX]

    Abstract: For studying the selective excitation of a particular fluorophore in fluorescence microscopy, the effect of the laser pulse chosen is immense. To study the ramifications of this selection, we present a thorough study of one-color stimulated emission depletion of the two-photon fluorescence of selective fluorophores by changing the wavelength and delay between two identical laser pulses.

     BibTeX: @article{royControlSelectiveTwophoton2022,
      title = {‪{{Control}} of Selective Two-Photon Fluorescence Suppression by One-Color Pulse-Pair Excitation‬},
      author = {Roy, Debjit and De, Arijit K. and Goswami, Debabrata},
      date = {2022},
      journaltitle = {Asian Journal of Physics},
      volume = {31},
      number = {3-5},
      pages = {475--478},
      url = {https://scholar.google.com/citations?view_op=view_citation&hl=en&user=OZ651FIAAAAJ&sortby=pubdate&citation_for_view=OZ651FIAAAAJ:jtI9f0ekYq0C},
      urldate = {2022-12-31}
    }
    

14. Advantage of Femtosecond Optical Tweezers. A. Singh, D. Kumar, K. K. Singh, and D. Goswami, in Frontiers in Optics + Laser Science 2022 (FIO, LS) (2022), Paper JW5A.26 (Optica Publishing Group, 2022), p. JW5A.26 [Abstract] [PDF] [BibTeX]

    Abstract: To highlight the advantage of femtosecond optical tweezers over conventional tweezers, we trapped 1µm diameter polystyrene beads suspended in water using a Ti:Sapphire laser.

     BibTeX: @inproceedings{singhAdvantageFemtosecondOptical2022,
      title = {Advantage of {{Femtosecond Optical Tweezers}}},
      booktitle = {Frontiers in {{Optics}} + {{Laser Science}} 2022 ({{FIO}}, {{LS}}) (2022), Paper {{JW5A}}.26},
      author = {Singh, Ajitesh and Kumar, Deepak and Singh, Krishna Kant and Goswami, Debabrata},
      date = {2022-10-17},
      pages = {JW5A.26},
      publisher = {{Optica Publishing Group}},
      url = {https://opg.optica.org/abstract.cfm?uri=FiO-2022-JW5A.26},
      urldate = {2022-12-31},
      eventtitle = {Frontiers in {{Optics}}}
    }
    

2021

1. Understanding the Photothermal Response of CBNP Nanofluids Using Thermal Lens Spectroscopic Techniques. S. Chakraborty, A. K. Mishra, A. K. Rawat, and D. Goswami, in Frontiers in Optics + Laser Science 2021 (2021), Paper JTu1A.99 (Optica Publishing Group, 2021), p. JTu1A.99 [Abstract] [PDF] [BibTeX]

   Abstract: We performed a dual beam Z-Scan experiment to examine the thermal lensing effects in CBNP nanofluids. The photothermal characteristics and heat dissipation dynamics were observed for these nanofluids at different levels of their linear absorption.

    BibTeX: @inproceedings{chakrabortyUnderstandingPhotothermalResponse2021,
     title = {Understanding the {{Photothermal Response}} of {{CBNP Nanofluids Using Thermal Lens Spectroscopic Techniques}}},
     booktitle = {Frontiers in {{Optics}} + {{Laser Science}} 2021 (2021), Paper {{JTu1A}}.99},
     author = {Chakraborty, Subhajit and Mishra, Amit Kumar and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2021-11-01},
     pages = {JTu1A.99},
     publisher = {{Optica Publishing Group}},
     doi = {10.1364/FIO.2021.JTu1A.99},
     url = {https://opg.optica.org/abstract.cfm?uri=LS-2021-JTu1A.99},
     urldate = {2022-12-31},
     eventtitle = {Laser {{Science}}}
   }
   

2. Semi-Supervised Approaches to Ultrafast Pulse Shaping. R. Goswami, A. Goswami, and D. Goswami, in ICOL-2019, K. Singh, A. K. Gupta, S. Khare, N. Dixit, and K. Pant, eds., Springer Proceedings in Physics (Springer, 2021), pp. 747–749 [Abstract] [PDF] [BibTeX]

   Abstract: Spatiotemporal control aspects of pulsed laser experiments rely on the ability to modulate the shape of the generated pulses efficiently. Drawing from current state-of-the-art theoretical aspects of computational simulations to reduce the sim-to-real bottlenecks, we devise a novel schematic for the generation of on-the-fly calibrated pulse trains with more accountability than existing techniques under the domain of optimal control theory. The techniques presented further diminish the divide between experiment and theory.

    BibTeX: @inproceedings{goswamiSemiSupervisedApproachesUltrafast2021,
     title = {Semi-{{Supervised Approaches}} to {{Ultrafast Pulse Shaping}}},
     booktitle = {{{ICOL-2019}}},
     author = {Goswami, Rohit and Goswami, Amrita and Goswami, Debabrata},
     editor = {Singh, Kehar and Gupta, A. K. and Khare, Sudhir and Dixit, Nimish and Pant, Kamal},
     date = {2021},
     series = {Springer {{Proceedings}} in {{Physics}}},
     pages = {747--749},
     publisher = {{Springer}},
     location = {{Singapore}},
     doi = {10.1007/978-981-15-9259-1_172},
     url = {10.1007/978-981-15-9259-1_172},
     isbn = {9789811592591}
   }
   

3. Using Femtosecond Coherent Oscillations to Unravel Dynamics of Complex Systems. D. Goswami, in ICOL-2019, K. Singh, A. K. Gupta, S. Khare, N. Dixit, and K. Pant, eds., Springer Proceedings in Physics (Springer, 2021), pp. 59–61 [Abstract] [PDF] [BibTeX]

   Abstract: Vibronic transitions of a molecular system in solution upon probing with ultrashort laser pulses (<40 fs), often creates coherent oscillations. These are either in the ground or excited state or in both the ground and excited states. Such vibrational coherence or coherent oscillation produced in the ground or excited states are often highly solvent dependent as these are characteristic of confinement and microheterogeneity in liquids.

    BibTeX: @inproceedings{goswamiUsingFemtosecondCoherent2021,
     title = {Using {{Femtosecond Coherent Oscillations}} to {{Unravel Dynamics}} of {{Complex Systems}}},
     booktitle = {{{ICOL-2019}}},
     author = {Goswami, Debabrata},
     editor = {Singh, Kehar and Gupta, A. K. and Khare, Sudhir and Dixit, Nimish and Pant, Kamal},
     date = {2021},
     series = {Springer {{Proceedings}} in {{Physics}}},
     pages = {59--61},
     publisher = {{Springer}},
     location = {{Singapore}},
     doi = {10/gjmht8},
     url = {10.1007/978-981-15-9259-1_14},
     isbn = {9789811592591}
   }
   

4. Unraveling Molecular Interactions in Binary Liquid Mixtures with Time-Resolved Thermal-Lens-Spectroscopy. A. K. Rawat, S. Chakraborty, A. K. Mishra, and D. Goswami, Journal of Molecular Liquids 336, 116322 (2021) [Abstract] [PDF] [BibTeX]

   Abstract: Non-contact localized laser heating-based thermal lensing has emerged as a technique for probing the heat transport in liquids. A mode-mismatched dual-beam pump–probe spectroscopic technique was employed to investigate the photothermal response and modes of heat dissipation in methanol and binary mixtures of methanol with polar (water, methanol (MeOH)) and nonpolar (CCl4) solvents. We recorded the time-resolved thermal lens (TL) signal of a probe beam at 780 nm after heat deposition by a 1560 nm pump beam. For pure solvents, the TL signal was found to be approximately one order of magnitude larger for methanol than for water, DMSO, or CCl4, implying that the energy deposition is larger for methanol than for any of the other solvents. Subsequently, binary mixtures were studied where the TL signal increased with an increase in the volume fraction of methanol. All TL signals are shown to have a physical interpretation in terms of heat conduction and convection. In the case of methanol–water, the observed trend can be rationalized in terms of a strong intermolecular interaction. Convective heat transfer is shown to dominate the overall heat transfer in pure methanol and in binary mixtures for all volume fractions where MeOH is in excess of 50%. No convection is observed for very dilute mixtures with a small amount of methanol; in this case, heat conduction is sufficient to reach equilibration. Interestingly, for binary mixtures of methanol with DMSO or water, a decreasing trend is observed in the concentration range between 90% and 100% volume fraction of methanol. We observe also that the TL signal is modified in case of intermolecular interactions forming large clusters of methanol with the cosolvent. In such cases, heat diffusion is affected. Thus, TL can be seen as a sensitive probe for intermolecular interactions as well.

    BibTeX: @article{rawatUnravelingMolecularInteractions2021,
     title = {Unraveling Molecular Interactions in Binary Liquid Mixtures with Time-Resolved Thermal-Lens-Spectroscopy},
     author = {Rawat, Ashwini Kumar and Chakraborty, Subhajit and Mishra, Amit Kumar and Goswami, Debabrata},
     date = {2021-08-15},
     journaltitle = {Journal of Molecular Liquids},
     shortjournal = {Journal of Molecular Liquids},
     volume = {336},
     pages = {116322},
     issn = {0167-7322},
     doi = {10.1016/j.molliq.2021.116322},
     url = {https://www.sciencedirect.com/science/article/pii/S0167732221010461},
     urldate = {2023-07-28}
   }
   

2020

1. Comparative Study of the Real-Time Optical Trapping in the Rayleigh Regime for Continuous and Pulsed Lasers. S. N. Bandyopadhyay, T. Gaur, and D. Goswami, (2020) [Abstract] [PDF] [BibTeX]

   Abstract: Simulating real-time scenarios to predict optical trapping behavior for continuous wave (CW) as well as femtosecond pulsed lasers is a challenging problem. This is especially so, because, for a tightly focused laser, one must also include optical Kerr effect as well as thermal nonlinearity. We show here the distinct differences between CW and femtosecond pulsed laser mediated optical trapping via their effect in scattering and gradient forces in the Rayleigh regime. In our newly developed model, it will also be easier to predict the stability of the trap in real optical trapping scenario as well as provide information regarding choice of solvents, probes, and optical parameters like laser type, power range, wavelength, etc. as may the cases be.

    BibTeX: @unpublished{bandyopadhyayComparativeStudyRealtime2020,
     title = {Comparative Study of the Real-Time Optical Trapping in the {{Rayleigh}} Regime for Continuous and Pulsed Lasers},
     author = {Bandyopadhyay, Soumendra Nath and Gaur, Tushar and Goswami, Debabrata},
     date = {2020-02-01},
     eprint = {2002.00227},
     eprinttype = {arxiv},
     eprintclass = {physics},
     url = {http://arxiv.org/abs/2002.00227},
     urldate = {2020-02-06}
   }
   

2. Organic-Inorganic Hybrid Halide Perovskites Impregnated with Group 1 and 15 Elements for Solar Cell Application. P. Dey, H. Singh, R. K. Gupta, D. Goswami, and T. Maiti, Journal of Physics and Chemistry of Solids 144, 109518 (2020) [Abstract] [PDF] [BibTeX]

   Abstract: In this report, we explored the substitution of triple cations at B-site of ABX3 perovskite architecture in inorganic-organic hybrid perovskite materials in order to improve its stability over moisture and heat, which is considered as the paramount obstacles for commercialization of perovskite solar cell. In the current investigation we synthesized two novel perovskite materials, Methylammonium potassium bismuth lead iodide [CH3NH3K0.25Bi0.25Pb0.5I3] (MKBPI) and Methylammonium sodium bismuth lead iodide [CH3NH3Na0.25Bi0.25Pb0.5I3] (MNBPI). XRD studies confirmed hexagonal crystal structure with P63/mmc space group for both the perovskites. Antisolvent treatment improved the surface coverage and morphology of the thin films, observed in FESEM. UV–Vis spectra demonstrated high absorption coefficient. Band gap was estimated as 2.09 eV for MKBPI. Fluorescence decay kinetics study revealed charge carrier lifetime on the order of nano second. DSC and TGA measurements confirmed thermal stability of these perovskites up to 280 °C. Further, we carried out detailed degradation study using XRD and UV–Vis spectroscopy of these perovskite thin films kept at ambient atmosphere for two weeks. Remarkably thin films of these perovskites exhibited good absorption even after 14 days.

    BibTeX: @article{deyOrganicinorganicHybridHalide2020,
     title = {Organic-Inorganic Hybrid Halide Perovskites Impregnated with {{Group}} 1 and 15 Elements for Solar Cell Application},
     author = {Dey, Pritam and Singh, Harish and Gupta, Rahul K. and Goswami, Debabrata and Maiti, Tanmoy},
     date = {2020-09-01},
     journaltitle = {Journal of Physics and Chemistry of Solids},
     shortjournal = {Journal of Physics and Chemistry of Solids},
     volume = {144},
     pages = {109518},
     issn = {0022-3697},
     doi = {10.1016/j.jpcs.2020.109518},
     url = {http://www.sciencedirect.com/science/article/pii/S0022369719327763},
     urldate = {2020-07-11}
   }
   

3. Vectorial Imaging Techniques for Insights into the Principles of Optical Tweezers. S. Dinda and D. Goswami, Asian Journal of Physics 28(10-12), 989–1013 (2020) [Abstract] [BibTeX]

   Abstract: Optical tweezers work on the principle that microscopic particles may be immobilized by the application of an intense photon flux, which may be attained under tight focusing conditions. To elucidate the behaviour and mechanism of this tweezing action, herein we perform numerical studies and investigate the intensity distribution at the focusing spot under tight focusing conditions. With a high numerical aperture optical lens, the influence of the incident beam polarization on the intensity distribution of focusing spot is very significant. A linearly polarized incident beam induces an asymmetric focusing spot, which is elongated along the polarization direction of the incident beam. The incident beam profile influences the shape of the focusing spot. We show here how introducing an optical mask in front of the optical lens can induce many impressive results; e.g., incident beam modulated by an amplitude mask induces a sub-diffraction limit focusing spot which is relevant to further studies on optical tweezers. We also demonstrate the effects of considering interfaces of different numerical apertures in an optical setup. Thus, we report on the multiple aspects of light-matter interactions for high numerical aperture lens setups, wherein we show through simulations and experiments, the characteristics of such systems that are of use to the broader optics community.

    BibTeX: @article{dindaVectorialImagingTechniques2020,
     title = {Vectorial Imaging Techniques for Insights into the Principles of Optical Tweezers},
     author = {Dinda, Sirshendu and Goswami, Debabrata},
     date = {2020-05-01},
     journaltitle = {Asian Journal of Physics},
     shortjournal = {Asian J. Phys.},
     volume = {28},
     number = {10-12},
     pages = {989--1013}
   }
   

4. Arthur Ashkin (1922–2020). S. Goswami and D. Goswami, Current Science 120(4), 726–728 (2020) [BibTeX]

    BibTeX: @article{goswamiArthurAshkin19222020,
     title = {Arthur {{Ashkin}} (1922–2020)},
     author = {Goswami, Sonaly and Goswami, Debabrata},
     date = {2020},
     journaltitle = {Current Science},
     volume = {120},
     number = {4},
     pages = {726--728},
     issn = {0028-0836, 1476-4687}
   }
   

5. Femtosecond Optical Tweezers for in Situ Tracking of Optically Directed Self-Assembly of Nanoclusters. D. Goswami, in (2020) [PDF] [BibTeX]

    BibTeX: @inproceedings{goswamiFemtosecondOpticalTweezers2020,
     title = {Femtosecond Optical Tweezers for in Situ Tracking of Optically Directed Self-Assembly of Nanoclusters},
     author = {Goswami, Debabrata},
     date = {2020-04-29},
     doi = {10.1021/scimeetings.0c03994},
     url = {https://www.morressier.com/article/5e735fe7cde2b641284aa286},
     urldate = {2020-07-11},
     eventtitle = {{{ACS Spring}} 2020 {{National Meeting}} \& {{Expo}}}
   }
   

6. Femtosecond Pump-Probe Spectroscopy for Remote Sensing of Liquid-Liquid Interface. D. Goswami, D. K. Das, and K. Makhal, Asian Journal of Physics 29(3 & 4), 313–319 (2020) [Abstract] [BibTeX]

   Abstract: We report results establishing that detection of the liquid-liquid interface is possible through femtosecond pump-probe spectroscopy. In particular, we use femtosecond laser pulses to pump and probe the dynamics of infra-red dye molecules in a liquid pair that can form an interface. We demonstrate that an interface formation can be detected from such femtosecond dynamical study of the dye molecule. The importance of obtaining the molecular description on the relation between the dynamics of solute molecules and solute-solvent interactions arises from the fact that the dynamic and static properties of dye molecules are strongly affected by the surrounding solvent molecules.

    BibTeX: @article{goswamiFemtosecondPumpprobeSpectroscopy2020,
     title = {Femtosecond Pump-Probe Spectroscopy for Remote Sensing of Liquid-Liquid Interface},
     author = {Goswami, Debabrata and Das, Dipak K. and Makhal, Krishnandu},
     date = {2020},
     journaltitle = {Asian Journal of Physics},
     volume = {29},
     pages = {313--319},
     issue = {3\&4}
   }
   

7. Nicolaas Bloembergen (1920–2017): Physicist, Father of Nonlinear Optics. D. Goswami, Resonance 25(12), 1653–1657 (2020) [PDF] [BibTeX]

    BibTeX: @article{goswamiNicolaasBloembergen19202020,
     title = {Nicolaas {{Bloembergen}} (1920–2017): {{Physicist}}, {{Father}} of {{Nonlinear Optics}}},
     shorttitle = {Nicolaas {{Bloembergen}} (1920–2017)},
     author = {Goswami, Debabrata},
     date = {2020-12},
     journaltitle = {Resonance},
     shortjournal = {Reson},
     volume = {25},
     number = {12},
     pages = {1653--1657},
     issn = {0971-8044, 0973-712X},
     doi = {10/gjmhvg},
     url = {http://link.springer.com/10.1007/s12045-020-1086-8},
     urldate = {2021-03-28}
   }
   

8. Sensing the Insensible Using Optical Schemes: Converting the Maze Problem into a Quantum Search Problem. D. Goswami, in Image Sensing Technologies: Materials, Devices, Systems, and Applications VII (International Society for Optics and Photonics, 2020), 11388, p. 113880L [Abstract] [PDF] [BibTeX]

   Abstract: Many large image processing and data processing scenarios can soon develop into maze problems requiring, say, finding the longest possible path, which are unresponsive, intractable, and challenging to analyze! Such maze problems, of which the traveling salesman decision problem is a special case, are of the Non-determinate Polynomial (NPcomplete) class of problems that are often impossible to solve with finite time and storage. We propose a novel methodology to approach this class of NP-complete problems. We convert a suitably formulated maze problem into a Quantum Search Problem (QSP), and the desired solutions are then sought using the iterative Grover’s Search Algorithm. Thus, we reformulate the entire class of such NP-problems into QSPs. Our current solution deals with two-dimensional perfect mazes with no closed loops. We encode all possible individual paths from the starting point of the maze into a quantum register. A quantum fitness operator applied to the register encodes each qubit with its fitness value. We propose the design of an optical oracle that marks all entities above a certain fitness value and uses the Grover search algorithm to find the optimal marked state in an iterative manner.

    BibTeX: @inproceedings{goswamiSensingInsensibleUsing2020,
     ids = {goswamiSensingInsensibleUsing2020a},
     title = {Sensing the Insensible Using Optical Schemes: Converting the Maze Problem into a Quantum Search Problem},
     shorttitle = {Sensing the Insensible Using Optical Schemes},
     booktitle = {Image {{Sensing Technologies}}: {{Materials}}, {{Devices}}, {{Systems}}, and {{Applications VII}}},
     author = {Goswami, Debabrata},
     date = {2020-04-23},
     volume = {11388},
     pages = {113880L},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10.1117/12.2563658},
     url = {10.1117/12.2563658},
     urldate = {2020-07-11},
     eventtitle = {Image {{Sensing Technologies}}: {{Materials}}, {{Devices}}, {{Systems}}, and {{Applications VII}}}
   }
   

9. Ultrafast Insights for Predictive Fragrance Compounding. D. Goswami, R. Goswami, A. Kumar Rawat, and D. Chakrabarty, in (2020) [PDF] [BibTeX]

    BibTeX: @inproceedings{goswamiUltrafastInsightsPredictive2020,
     title = {Ultrafast Insights for Predictive Fragrance Compounding},
     author = {Goswami, Debabrata and Goswami, Rohit and Kumar Rawat, Ashwini and Chakrabarty, Debojit},
     date = {2020-04-29},
     doi = {10.1021/scimeetings.0c03998},
     url = {https://www.morressier.com/article/5e73d6ce139645f83c2299c8},
     urldate = {2020-07-11},
     eventtitle = {{{ACS Spring}} 2020 {{National Meeting}} \& {{Expo}}}
   }
   

10. Two-Photon-Induced Fluorescence Study of Rhodamine-6G Dye in Different Sets of Binary Solvents. R. K. Gupta, S. Kant, A. K. Rawat, and D. Goswami, Journal of Fluorescence (2020) [Abstract] [PDF] [BibTeX]

    Abstract: This study deals with the effects of different sets of binary solvents on the Two-Photon Induced Fluorescence (TPIF), a non-linear process, of the Rhodamine-6G (Rh6G) dye, which is a well-known xanthene dye. This work examines the importance of inter-molecular interactions, which results in the modulation of the TPIF of the Rh6G. In this work, we have investigated three binary solvent mixtures representing varying polarity and intermolecular interactions. Specific solvent mixtures used are methanol-water, methanol-dimethyl formamide, and methanol-chloroform. Since the solvent polarity across these binary solvents differs, there are significant intermolecular interactions in the binary mixture solvents, which modulate the two-photon process of Rh6G when irradiated with high-intensity laser light at 780 nm. In our studies, we find that Rh6G in the MeOH-H2O binary solvent has maximum red-shift and minimum intensity as compared to other pairs of binary liquids when the volume fraction of methanol decreases due to more extensive hydrogen bonding between the two components. Additionally, at 1:1 ratio of binary mixtures, Rh6G is found to have the highest TPEACS value for methanol-chloroform binary solvent and reason for that is related to the formation of weak H-bond networks between proton donor chloroform and proton acceptor methanol.

     BibTeX: @article{guptaTwoPhotonInducedFluorescenceStudy2020,
      ids = {guptaTwoPhotonInducedFluorescenceStudy2020a},
      title = {Two-{{Photon-Induced Fluorescence Study}} of {{Rhodamine-6G Dye}} in {{Different Sets}} of {{Binary Solvents}}},
      author = {Gupta, Rahul Kumar and Kant, Surya and Rawat, Ashwini Kumar and Goswami, Debabrata},
      date = {2020-07-01},
      journaltitle = {Journal of Fluorescence},
      shortjournal = {J Fluoresc},
      issn = {1573-4994},
      doi = {10.1007/s10895-020-02577-0},
      url = {10.1007/s10895-020-02577-0},
      urldate = {2020-07-11}
    }
    

11. Unraveling the Molecular Dependence of Femtosecond Laser-Induced Thermal Lens Spectroscopy in Fluids. S. Singhal and D. Goswami, The Analyst 10.1039.C9AN01082C (2020) [Abstract] [PDF] [BibTeX]

    Abstract: Fluid systems exhibit thermal lens effects due to laser irradiation accompanied by convection and in contrast primarily conductive heat dissipation is observed in solids. , Fluid systems exhibit thermal lens effects due to laser irradiation accompanied by convection and in contrast primarily conductive heat dissipation is observed in solids. The presence of a significant convective mode modifies the temperature gradient in fluids resulting in a deviation of the experimental results from theories that are based on pure conduction. Herein, we present a carefully designed femtosecond laser experiment that keeps the heat generation process constant in order to account for the effect of molecular properties on thermal dissipation. We derive a theoretical model that introduces and characterizes the additional convective heat transfer in thermal lens (TL) spectroscopy which explains our observed experimental results. We measured the TL signal for a series of liquid aliphatic alkanes, ranging from hexane to decane, and their comparison has proven the validity of our model. The influence of convective heat transfer on the TL signal is predicted in terms of the dimensionless Peclet number ( P E ). The lower values of P E for alkanes with longer carbon chains indicate that the convective flow of heat slows down substantially for larger molecules.

     BibTeX: @article{singhalUnravelingMolecularDependence2020,
      title = {Unraveling the Molecular Dependence of Femtosecond Laser-Induced Thermal Lens Spectroscopy in Fluids},
      author = {Singhal, Sumit and Goswami, Debabrata},
      date = {2020},
      journaltitle = {The Analyst},
      shortjournal = {Analyst},
      pages = {10.1039.C9AN01082C},
      issn = {0003-2654, 1364-5528},
      doi = {10/ggfxvz},
      url = {http://xlink.rsc.org/?DOI=C9AN01082C},
      urldate = {2019-12-28}
    }
    

2019

1. Sensing the Molecular Properties in Methanol and Its Binary Mixtures Using Time-Resolved Thermal Lens Spectrometer. S. Chakraborty, A. K. Rawat, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–3 [Abstract] [BibTeX]

   Abstract: Mode Mismatched Pump-Probe spectroscopic method was employed to examine the thermally induced nonlinear optical properties of methanol and its binary mixtures. The heat transfer mechanism in methanol and its binary mixtures with carbon tetrachloride (CCl4) at different concentrations of methanol is investigated. Methanol has the highest Thermal Lens (TL) signal, and CCl4 does not have any TL signal at all. However, the presence of CCl4 modulates the TL signal of the binary mixture. The time-domain shift in TL signal is observed for different concentrations of methanol, which indicates the unusual molecular behavior in the binary mixture.

    BibTeX: @inproceedings{chakrabortySensingMolecularProperties2019,
     title = {Sensing the {{Molecular Properties}} in {{Methanol}} and Its {{Binary Mixtures}} Using {{Time-Resolved Thermal Lens Spectrometer}}},
     booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Chakraborty, Subhajit and Rawat, Ashwini Kumar and Goswami, Debabrata},
     date = {2019-12},
     pages = {1--3},
     issn = {null},
     doi = {10.1109/WRAP47485.2019.9013697},
     eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

2. Rapid Programmable Pulse Shaping of Femtosecond Pulses at the MHz Repetition Rate. S. Dinda, S. N. Bandyopadhyay, and D. Goswami, OSA Continuum 2(4), 1386 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: We have shown experimentally the successful engineering of femtosecond pulse shaping at a 76 MHz repetition rate input pulse with an acousto-optic modulator (AOM). High repetition rate (HRR) femtosecond laser pulse shaping using an AOM in the Fourier plane was incomprehensible because of its intrinsic 100 kHz acoustic update limit. We demonstrate an effective way of pulse selection and a calibration routine (Fourier shift theorem), which enables generation of ∼10 MHz shaped output pulses from the HRR input pulse train. We have generated a temporally shifted rectangular shaped pulse profile by applying modulation on both the phase and amplitude of the ‘sinc’ RF modulation function.

    BibTeX: @article{dindaRapidProgrammablePulse2019,
     title = {Rapid Programmable Pulse Shaping of Femtosecond Pulses at the {{MHz}} Repetition Rate},
     author = {Dinda, Sirshendu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2019-04-15},
     journaltitle = {OSA Continuum},
     shortjournal = {OSA Continuum},
     volume = {2},
     number = {4},
     pages = {1386},
     issn = {2578-7519},
     doi = {10/gf4gtf},
     url = {https://www.osapublishing.org/abstract.cfm?URI=osac-2-4-1386},
     urldate = {2019-06-30}
   }
   

3. Manifesting the Effects of Thermal Nonlinearity in Optical Trapping for Rayleigh Regime. T. Gaur, S. N. Bandyopadhyay, and D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (IEEE, 2019), pp. 1–5 [Abstract] [PDF] [BibTeX]

   Abstract: Since long the thermal effects have not been much explored in the optical trapping theory, in this paper, we are establishing the effects of optically induced thermal nonlinearity in the medium of optical trapping in the Rayleigh regime for both continuous wave and a pulsed laser. For a single beam, optical tweezers with high numerical aperture (N.A.) objectives are used as a routine. In such a tight focusing scenario, both optical nonlinearity and thermal effects may prevail in the cases of continuous wave (C.W.) and pulsed laser-mediated optical trapping events. In this paper we will introduce the effects sequentially, starting from optical nonlinearity and methods to implement this effect and subsequently introduce the thermal nonlinearity in the medium. The effects are significantly different when compared between CW and pulsed optical tweezers and will be discussed in detail in this paper.

    BibTeX: @inproceedings{gaurManifestingEffectsThermal2019,
     title = {Manifesting the {{Effects}} of {{Thermal Nonlinearity}} in {{Optical Trapping}} for {{Rayleigh Regime}}},
     booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     author = {Gaur, Tushar and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2019-03},
     pages = {1--5},
     publisher = {{IEEE}},
     location = {{New Delhi, India}},
     doi = {10/gf5mqf},
     url = {https://my.pcloud.com/publink/show?code=XZqaxr7ZmnVNxAn4Y4mRbGS3d4A7FjmCWEv7},
     urldate = {2019-08-01},
     eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     isbn = {978-90-825987-5-9}
   }
   

4. Femtosecond Laser Induced Spatiotemporal Control for Remote Sensing and Computation at Nanoscale. D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (IEEE, 2019), pp. 1–1 [PDF] [BibTeX]

    BibTeX: @inproceedings{goswamiFemtosecondLaserInduced2019,
     title = {Femtosecond {{Laser Induced Spatiotemporal Control}} for {{Remote Sensing}} and {{Computation}} at {{Nanoscale}}},
     booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     author = {Goswami, Debabrata},
     date = {2019-03},
     pages = {1--1},
     publisher = {{IEEE}},
     location = {{New Delhi, India}},
     doi = {10/gf5mp6},
     url = {https://my.pcloud.com/publink/show?code=XZyvxr7ZOeecG9i7bDyhB3UKkH2KEbJ5Bd87},
     urldate = {2019-08-01},
     eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     isbn = {978-90-825987-5-9}
   }
   

5. Qubit Network Barriers to Deep Learning. R. Goswami, A. Goswami, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–3 [Abstract] [BibTeX]

   Abstract: The popularity of artificial neural networks (ANNs) of great depth and Quantum computing have led to many speculations as to their convergence. We enumerate barriers to utilizing qubit networks for deep learning architectures. We also describe the criteria for an effective usage of qubit networks and then assert that the bottleneck in their implementation is a lack of quantum algorithms for utilizing the topology of a deep neural network.

    BibTeX: @inproceedings{goswamiQubitNetworkBarriers2019,
     title = {Qubit {{Network Barriers}} to {{Deep Learning}}},
     booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Goswami, Rohit and Goswami, Amrita and Goswami, Debabrata},
     date = {2019-12},
     pages = {1--3},
     issn = {null},
     doi = {10.1109/WRAP47485.2019.9013687},
     eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

6. Sensitive Detection of Phase Separation with Femtosecond Thermal Lens Spectroscopy. S. Goswami, S. Singhal, A. Banerjee, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–2 [Abstract] [BibTeX]

   Abstract: Femtosecond Thermal Lens Spectroscopy (FTLS) has been developed to a level of sensitivity that can have molecule specific response due to convection as demonstrated experimentally and theoretically. Within this framework, we show here that it is possible to use this technique for sensitive detection of liquid versus gas phase. Experimental demonstration is made with a single beam FTLS experiment of traces of iodine in pentane mixture in liquid versus its vapor phase.

    BibTeX: @inproceedings{goswamiSensitiveDetectionPhase2019,
     title = {Sensitive {{Detection}} of {{Phase Separation}} with {{Femtosecond Thermal Lens Spectroscopy}}},
     booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Goswami, Sonaly and Singhal, Sumit and Banerjee, Arup and Goswami, Debabrata},
     date = {2019-12},
     pages = {1--2},
     issn = {null},
     doi = {10.1109/WRAP47485.2019.9013833},
     eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

7. Space Filling Curves: Heuristics For Semi Classical Lasing Computations. R. Goswami, A. Goswami, and D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (IEEE, 2019), pp. 1–4 [Abstract] [PDF] [BibTeX]

   Abstract: For semi classical lasing, the FDTD (finite difference time domain) formulation including nonlinearities is often used. We determine the computational efficiency of such schemes quantitatively and present a hueristic based on space filling curves to minimize complexity. The sparse matrix kernel is shown to be optimized by the utilization of Bi-directional Incremental Compressed Row Storage (BICRS). Extensions to high performance clusters and parallelization are also derived.

    BibTeX: @inproceedings{goswamiSpaceFillingCurves2019,
     title = {Space {{Filling Curves}}: {{Heuristics For Semi Classical Lasing Computations}}},
     shorttitle = {Space {{Filling Curves}}},
     booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     author = {Goswami, Rohit and Goswami, Amrita and Goswami, Debabrata},
     date = {2019-03},
     pages = {1--4},
     publisher = {{IEEE}},
     location = {{New Delhi, India}},
     doi = {10/gf5mqk},
     url = {https://my.pcloud.com/publink/show?code=XZ8vxr7ZHFxXSXuD2J4ntMcQoyPGXFodmegy},
     urldate = {2019-08-01},
     eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
     isbn = {978-90-825987-5-9}
   }
   

8. Visualizing Colloidal Aggregation with Femtosecond Optical Tweezers. D. Goswami, in Optical Trapping and Optical Micromanipulation XVI (International Society for Optics and Photonics, 2019), 11083, p. 110832C [Abstract] [PDF] [BibTeX]

   Abstract: Optical tweezers manipulate microscopic objects using forces arising from the subtle interplay of optical scattering and gradient forces of highly focused laser beams. Unlike conventional backscatter signal for optical tweezers, the twophoton fluorescence (TPF) trapping signal from femtosecond optical tweezers (FOTs) shows a slow counterintuitive decay, when the trapped particles are not entirely within the laser-illuminated volume. A change in the corner frequency of FOT is also noted with the TPF technique. These observations are evident even at low average powers. The high peak powers trap not only single microspheres but also encourage optically directed self-assembly. We use TPF signatures of trapped particles to show the existence of a directed self-assembly process and elucidate the structural dynamics during the process of cluster formation.

    BibTeX: @inproceedings{goswamiVisualizingColloidalAggregation2019,
     title = {Visualizing Colloidal Aggregation with Femtosecond Optical Tweezers},
     booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XVI}}},
     author = {Goswami, Debabrata},
     date = {2019-09-09},
     volume = {11083},
     pages = {110832C},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/gf874x},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11083/110832C/Visualizing-colloidal-aggregation-with-femtosecond-optical-tweezers/10.1117/12.2528518.short},
     urldate = {2019-10-02},
     eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XVI}}}
   }
   

9. Excited State Absorption and Relaxation Dynamics in a Series of Heptamethine Dyes under Femtosecond and Nanosecond Excitations. K. Makhal, S. Maurya, and D. Goswami, Physica Scripta 94(9), 095501 (2019) [Abstract] [PDF] [BibTeX]

   Abstract: We show that the near-infrared-absorbing polymethine cyanine dyes exhibit nonlinear absorption (NLA) in the visible region, where they have negligible or very low linear absorption. In chloroform solvent, the studied cyanines were found to be photo-unstable and exhibited photo-degradation under prolonged exposures as compared to methanol and dimethyl sulphoxide solvents, where they were stable. Excitation with femtosecond (fs) pulses in the visible region (400–750 nm) exhibits excited state absorption (ESA) as characterized by positive differential absorption (ΔOD) in transient absorption signal. Non-resonant excitations in the visible region are governed by reverse saturable absorption (RSA) mechanism leading to ESA. Excitation with nanosecond pulses also shows NLA owing to ESA from triplet states as compared to that from singlet states under fs excitations. Single beam Z-scan studies were performed with nanosecond (ns) pulses to evaluate ground (σ gr) and excited state (σ ex) absorption cross-sections, which confirms the mechanism of RSA as σ ex were found to be greater than σ gr. The population relaxation from higher excited singlet states shows ultrafast behavior with multi-exponential decay components. The fast time component decay varies from a few hundreds of fs (τ 1) to some hundreds of picoseconds (τ 2), and the long-time decay is in the ns domain (τ 3).

    BibTeX: @article{makhalExcitedStateAbsorption2019,
     title = {Excited State Absorption and Relaxation Dynamics in a Series of Heptamethine Dyes under Femtosecond and Nanosecond Excitations},
     author = {Makhal, Krishnandu and Maurya, Sidharth and Goswami, Debabrata},
     date = {2019-06},
     journaltitle = {Physica Scripta},
     shortjournal = {Phys. Scr.},
     volume = {94},
     number = {9},
     pages = {095501},
     issn = {1402-4896},
     doi = {10/gf5mpz},
     url = {https://doi.org/10.1088%2F1402-4896%2Fab0064},
     urldate = {2019-08-01}
   }
   

10. Effect of Femtosecond Laser Pulse Repetition Rate on Nonlinear Optical Properties of Organic Liquids. S. K. Maurya, D. Yadav, and D. Goswami, PeerJ Physical Chemistry 1, e1 (2019) [Abstract] [PDF] [BibTeX]

    Abstract: The effect of the repetition rate of femtosecond laser pulses on the two-photon absorption and nonlinear refraction of pure organic liquids is presented using the conventional Z-scan technique. Such a study provides a way to determine the nature of light-matter interaction, explicitly enabling the identification of the linear versus nonlinear regimes. Based on the type of light-matter interaction, we have identified the thermal load dissipation time for the organic liquids. Our experimental results are in good agreement with the theoretically calculated decay time for the dissipation of thermal load.

     BibTeX: @article{mauryaEffectFemtosecondLaser2019,
      title = {Effect of Femtosecond Laser Pulse Repetition Rate on Nonlinear Optical Properties of Organic Liquids},
      author = {Maurya, Sandeep Kumar and Yadav, Dheerendra and Goswami, Debabrata},
      date = {2019-10-15},
      journaltitle = {PeerJ Physical Chemistry},
      volume = {1},
      pages = {e1},
      doi = {10/ggbzhh},
      url = {https://peerj.com/articles/pchem-1},
      urldate = {2019-10-29}
    }
    

11. Elucidating Optical Field Directed Hierarchical Self-Assembly of Homogenous versus Heterogeneous Nanoclusters with Femtosecond Optical Tweezers. D. Mondal, S. N. Bandyopadhyay, and D. Goswami, PLOS ONE 14(10), e0223688 (2019) [Abstract] [PDF] [BibTeX]

    Abstract: Insights into the morphology of nanoclusters would facilitate the design of nano-devices with improved optical, electrical, and magnetic responses. We have utilized optical gradient forces for the directed self-assembly of colloidal clusters using high-repetition-rate femtosecond laser pulses to delineate their structure and dynamics. We have ratified our experiments with theoretical models derived from the Langevin equation and defined the valid ranges of applicability. Our femtosecond optical tweezer-based technique characterizes the in-situ formation of hierarchical self-assembled clusters of homomers as well as heteromers by analyzing the back focal plane displacement signal. This technique is able to efficiently distinguish between nano-particles in heterogeneous clusters and is in accordance with our theory. Herein, we report results from our technique, and also develop a model to describe the mechanism of such processes where corner frequency changes. We show how the corner frequency changes enables us to recognize the structure and dynamics of the coagulation of colloidal homogeneous and heterogeneous clusters in condensed media over a broad range of nanoparticle sizes. The methods described here are advantageous, as the backscatter position-sensitive detection probes the in-situ self-assembly process while other light scattering approaches are leveraged for the characterization of isolated clusters.

     BibTeX: @article{mondalElucidatingOpticalField2019,
      title = {Elucidating Optical Field Directed Hierarchical Self-Assembly of Homogenous versus Heterogeneous Nanoclusters with Femtosecond Optical Tweezers},
      author = {Mondal, Dipankar and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
      date = {2019-10-31},
      journaltitle = {PLOS ONE},
      shortjournal = {PLOS ONE},
      volume = {14},
      number = {10},
      pages = {e0223688},
      issn = {1932-6203},
      doi = {10/ggfxvx},
      url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0223688},
      urldate = {2019-12-28}
    }
    

12. Polarization Induced Control of Optical Trap Potentials in Binary Liquids. D. Mondal, S. Dinda, S. N. Bandyopadhyay, and D. Goswami, Scientific Reports 9(1), 700 (2019) [PDF] [BibTeX]

     BibTeX: @article{mondalPolarizationInducedControl2019,
      title = {Polarization Induced Control of Optical Trap Potentials in Binary Liquids},
      author = {Mondal, Dipankar and Dinda, Sirshendu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
      date = {2019-12},
      journaltitle = {Scientific Reports},
      shortjournal = {Sci Rep},
      volume = {9},
      number = {1},
      pages = {700},
      issn = {2045-2322},
      doi = {10/gf5mqb},
      url = {http://www.nature.com/articles/s41598-018-36856-5},
      urldate = {2019-08-01}
    }
    

13. Thermal Inflection Study of Methanol-Hexane Mixtures Using Time-Resolved Thermal Lens Technique. A. K. Rawat, S. Chakraborty, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–3 [Abstract] [PDF] [BibTeX]

    Abstract: Time-resolved thermal lens (TL) technique is used to measure the heat transfer in pure methanol and its binary mixtures with hexane. We used dual-beam mode mismatched pump-probe scheme where a femtosecond laser beam of 1560 nm was used as a pump beam, and its frequency-doubled 780 nm beam was used as probe beam. TL Signal decreases with increasing concentration of hexane in the binary mixture. On higher concentration of Hexane in binary mixture then we have found convective heat transfer mode was absent. At 40%-60% methanol hexane mixture, we observed a sudden curious jump in TL signal.

     BibTeX: @inproceedings{rawatThermalInflectionStudy2019,
      ids = {rawatThermalInflectionStudy2019a},
      title = {Thermal {{Inflection Study}} of {{Methanol-Hexane Mixtures}} Using {{Time-Resolved Thermal Lens Technique}}},
      booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Rawat, Ashwini Kumar and Chakraborty, Subhajit and Goswami, Debabrata},
      date = {2019-12},
      pages = {1--3},
      issn = {null},
      doi = {10.1109/WRAP47485.2019.9013736},
      url = {10.1109/WRAP47485.2019.9013736},
      eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

14. Molecular Size and Mass Sensitive Femtosecond Thermal Spectrometer. S. Singhal, S. Goswami, A. Banerjee, and D. Goswami, in 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC) (2019), pp. 1–3 [Abstract] [BibTeX]

    Abstract: Though a single ultrashort pulse has inconceivable thermal effect, highly repetitive femtosecond lasers often result in some heating effects. Instead of fretting over the thermal effect, we have used this to develop the time-resolved photothermal lens spectroscopy for molecular sensitivity.

     BibTeX: @inproceedings{singhalMolecularSizeMass2019,
      title = {Molecular {{Size}} and {{Mass Sensitive Femtosecond Thermal Spectrometer}}},
      booktitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})},
      author = {Singhal, Sumit and Goswami, Sonaly and Banerjee, A. and Goswami, Debabrata},
      date = {2019-03},
      pages = {1--3},
      doi = {10/gf5mqh},
      eventtitle = {2019 {{URSI Asia-Pacific Radio Science Conference}} ({{AP-RASC}})}
    }
    

15. Thermal Lens Study of NIR Femtosecond Laser-Induced Convection in Alcohols. S. Singhal and D. Goswami, ACS Omega 4(1), 1889–1896 (2019) [Abstract] [PDF] [BibTeX]

    Abstract: We use time-resolved thermal lens (TL) experiments to examine the convective heat transfer at microscale in the first eight members of the homologous series of primary alcohols. TL measurements enable a direct study of these primary alcohols without adding any chromophore as a function of varying heat loads created via femtosecond laser pulses at 1560 nm. Convective heat transfer leads to the asymmetrical and reduced thermal gradient, which substantially weakens the TL signal. The inflection in the time profile of the TL signal of methanol at higher powers is attributed to the greater molecular convection in methanol compared to other samples. This inflection dies out with a decrease in laser power. Our results demonstrate that the convection is more prominent at higher laser powers in all samples, and it modifies the trend in the steady-state TL signal of different alcohols with pump laser power. Methanol also has the highest steady-state TL among the primary alcohol series at low laser powers. The maxima in the TL signal are shifted systematically from methanol to ethanol and then to propanol as the laser power increases. Semiempirical analysis of time-resolved TL signal by using the latest theoretical TL model enabled us to extract the coefficient of convective heat transfer in methanol at different laser powers. In addition to that, analysis of other members of alcohol series at the highest (7.3 mW) laser power shows that convection is more facile in short-chain alcohols compared to the long-chain alcohols.

     BibTeX: @article{singhalThermalLensStudy2019,
      title = {Thermal {{Lens Study}} of {{NIR Femtosecond Laser-Induced Convection}} in {{Alcohols}}},
      author = {Singhal, Sumit and Goswami, Debabrata},
      date = {2019-01-31},
      journaltitle = {ACS Omega},
      shortjournal = {ACS Omega},
      volume = {4},
      number = {1},
      pages = {1889--1896},
      issn = {2470-1343, 2470-1343},
      doi = {10/gf5mp4},
      url = {http://pubs.acs.org/doi/10.1021/acsomega.8b02956},
      urldate = {2019-08-01}
    }
    

16. Study of Starch Using Bright Field and Polarized Light Microscopy. K. K. Singh, Y. Yadav, D. Kumar, A. Singh, and D. Goswami, in 2019 Workshop on Recent Advances in Photonics (WRAP) (2019), pp. 1–2 [Abstract] [BibTeX]

    Abstract: Starch is a polymer derived from plants that have various applications. There are various types of starch available like potato, maize, tapioca, and wheat, etc. We have studied and successfully differentiated tapioca and maize starch using polarized light microscopy and bright field techniques with the help of Iodine staining. Starch granules are suspended in aqueous or non-aqueous media for polarized light and bright field microscopy. The botanical source of the starch is identified according to the shape and size of granules, granule surface marking, the position of hilum, iodine staining, and the presence of maltase crosses under polarized light.

     BibTeX: @inproceedings{singhStudyStarchUsing2019,
      title = {Study of {{Starch Using Bright Field}} and {{Polarized Light Microscopy}}},
      booktitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Singh, Krishna Kant and Yadav, Yogendra and Kumar, Deepak and Singh, Ajitesh and Goswami, Debabrata},
      date = {2019-12},
      pages = {1--2},
      issn = {null},
      doi = {10.1109/WRAP47485.2019.9013741},
      eventtitle = {2019 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

2018

1. Interactions between Micro-Scale Oil Droplets in Aqueous Surfactant Solution Determined Using Optical Tweezers. A. Chen, S.-W. Li, F.-N. Sang, H.-B. Zeng, and J.-H. Xu, Journal of Colloid and Interface Science 532, 128–135 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: Hypothesis The stability of the emulsions is crucial, which relies on a well-developed understanding of dynamic interaction forces between single dispersed droplets. In the previous studies, many interests focus on the oil droplets of size range of 20–200 µm. However, emulsion droplets with diameter below 10 µm are rarely mentioned, which is the size scale of real emulsion droplets in various applications, such as toners, spacers for liquid crystal displays, and materials in biomedical and biochemical analysis. The micro-scale droplets have many differences on the deformation, internal pressure and hydrodynamic effects. It is necessary to understand the interaction mechanisms between two real size scales of oil droplets for guiding practical production and application. Experiments In this work, tetradecane was chosen as the model oil phase in all experiments. The interaction forces of two tetradecane droplets with the diameter of 5.0 µm in water in the presence of surfactant and salt solution were directly measured using optical tweezers. The force-distance curves were established, and the zeta potential of tetradecane droplets was studied using Zetasizer Nano ZSP. Findings The absolute value of zeta potential of tetradecane droplets was found to decrease with the increase of salt concentration and increase with the increase of surfactant concentration. The repulsive force between two tetradecane droplets was found to decrease with the increase of salt concentration because the electrostatic double-layer force was suppressed gradually with the increase of salt concentration. The “hydrodynamic suction” effect during the process of retraction becomes more pronounced due to the corresponding increase in the hydrodynamic force with the increase of the approaching velocity between the tetradecane droplets. Furthermore, we found the existing model for the measurement of large droplets by atomic force microscope (AFM) is invalid for the measurement of micro-scale droplets by optical tweezers. The deformation of colliding micro-scale droplets can be safely ignored, which is quite different from the large droplets. Our results provide a useful method to study the interaction forces between micro-scale emulsion droplets with pN force resolution, and gives a deep insight of the stabilization mechanism of real size scale of O/W emulsions. These findings have significant implications on the stability of emulsions in many food, cosmetics, medicine, and advanced materials.

    BibTeX: @article{chenInteractionsMicroscaleOil2018,
     title = {Interactions between Micro-Scale Oil Droplets in Aqueous Surfactant Solution Determined Using Optical Tweezers},
     author = {Chen, An and Li, Shao-Wei and Sang, Fu-Ning and Zeng, Hong-Bo and Xu, Jian-Hong},
     date = {2018-12-15},
     journaltitle = {Journal of Colloid and Interface Science},
     shortjournal = {Journal of Colloid and Interface Science},
     volume = {532},
     pages = {128--135},
     issn = {0021-9797},
     doi = {10/gf85zg},
     url = {http://www.sciencedirect.com/science/article/pii/S0021979718308804},
     urldate = {2019-10-01}
   }
   

2. Observing Ground State Vibrational Coherence and Excited State Relaxation Dynamics of a Cyanine Dye in Pure Solvents. D. K. Das, K. Makhal, and D. Goswami, Physical Chemistry Chemical Physics 20(19), 13400–13411 (2018) [PDF] [BibTeX]

    BibTeX: @article{dasObservingGroundState2018,
     title = {Observing Ground State Vibrational Coherence and Excited State Relaxation Dynamics of a Cyanine Dye in Pure Solvents},
     author = {Das, Dipak Kumar and Makhal, Krishnandu and Goswami, Debabrata},
     date = {2018},
     journaltitle = {Physical Chemistry Chemical Physics},
     volume = {20},
     number = {19},
     pages = {13400--13411},
     doi = {10/gf5mqz},
     url = {https://my.pcloud.com/publink/show?code=XZ1Axr7ZxiTGNbfEV1bmLPqho9PtQzSq3qUk},
     urldate = {2019-08-01}
   }
   

3. Solvent Effect on Multiple Emission and Ultrafast Dynamics of Higher Excited States. D. K. Das, K. Makhal, and D. Goswami, Chemical Physics Letters 706, 375–379 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: We present ultrafast-depopulation-dynamics of higher-lying-excited-states using femtosecond fluorescence up-conversion techniques for two near-infrared (NIR) tricarbocyanine dyes (IR144 and IR140) in primary alcohols. With visible excitation wavelengths, such dyes show two distinct emission-bands with large peak wavelength difference: one at the visible region: S2\,→ S0, and the other at NIR region: S1\,→ S0. We show that exact band-positions, intensities, and fluorescence-decay-timescales (τ) depend strongly on viscosity and polarity of solvents. Interestingly, though the faster component of τ increased for IR144 with increasing viscosity and chain-length of alcohols, the reverse was seen for IR140, indicating the possible formation of ion-pair of IR140 with alcohols.

    BibTeX: @article{dasSolventEffectMultiple2018,
     title = {Solvent Effect on Multiple Emission and Ultrafast Dynamics of Higher Excited States},
     author = {Das, Dipak Kumar and Makhal, Krishnandu and Goswami, Debabrata},
     date = {2018-08-16},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {706},
     pages = {375--379},
     issn = {0009-2614},
     doi = {10/gd3phb},
     url = {https://my.pcloud.com/publink/show?code=XZOAxr7ZeXIX0Ahn0DBrmUdo3wS0tyDPhbz7},
     urldate = {2019-08-01}
   }
   

4. Two Photon Spectroscopy Can Serve as a Marker of Protein Denaturation Pathway. D. K. Das, S. I. Islam, N. Samanta, Y. Yadav, D. Goswami, and R. K. Mitra, Journal of Fluorescence 28(3), 855–862 (2018) [PDF] [BibTeX]

    BibTeX: @article{dasTwoPhotonSpectroscopy2018,
     title = {Two {{Photon Spectroscopy Can Serve}} as a {{Marker}} of {{Protein Denaturation Pathway}}},
     author = {Das, Dipak Kumar and Islam, Sk Imadul and Samanta, Nirnay and Yadav, Yogendra and Goswami, Debabrata and Mitra, Rajib Kumar},
     date = {2018-05},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {28},
     number = {3},
     pages = {855--862},
     issn = {1053-0509, 1573-4994},
     doi = {10/gd2g84},
     url = {https://my.pcloud.com/publink/show?code=XZGNxr7ZDvT2qqOXdaJrTjbB8A2tB5nJ8kH7},
     urldate = {2019-08-01}
   }
   

5. Nobel Prize in Physics – 2018. D. Goswami, 9 (2018) [PDF] [BibTeX]

    BibTeX: @article{goswamiNobelPrizePhysics2018,
     title = {Nobel {{Prize}} in {{Physics}} – 2018},
     author = {Goswami, Debabrata},
     date = {2018},
     pages = {9},
     doi = {10/gf5mqq},
     url = {https://my.pcloud.com/publink/show?code=XZ3Gxr7Z2FLRny10VRFK6F48uNi7pYpeSmty}
   }
   

6. Solvent Effect on Dual Fluorescence and the Corresponding Excited State Dynamics. D. Goswami, D. K. Das, and K. Makhal, in Reviews in Fluorescence 2017, C. D. Geddes, ed., Reviews in Fluorescence (Springer International Publishing, 2018), pp. 145–160 [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast depopulation dynamics of highly excited states of near-infrared (NIR) tri-carbocyanine dyes is presented in primary alcohols using the femtosecond fluorescence upconversion technique. Pronounced solvent dependence is observed in the dynamics of the highly excited states. Typically, the tri-carbocyanine dyes have strong absorption and fluorescence with a single peak in the NIR region, however, on tuning the excitation wavelength to the visible region, two distinct emission bands are seen with a large peak wavelength difference. Such dual fluorescent peaks correspond to the respective transitions: S2 → S0 for the visible region and S1 → S0 for the NIR region. The exact fluorescent band positions or their intensities strongly depend on the viscosity and polarity of the solvents. The fluorescence decay timescales measured using fluorescence upconversion techniques with femtosecond time resolution also vary significantly as a function of solvent polarity. The faster decay on the ~250 fs and slower decay on the order of picosecond timescale was found which are strongly depending with increasing the chain length of alcohol. Specifically, for example, in the IR144 dye, the faster decay time constant (τ1) increase with the increase in the viscosity and chain length of the alcohol while, in the case of the IR140 dye, we noticed that the τ1 value decreases with increasing viscosity and chain length of alcohols. We invoke the ion-pair formation of IR140 dye with alcohols to explain such behavior.

    BibTeX: @incollection{goswamiSolventEffectDual2018,
     title = {Solvent {{Effect}} on {{Dual Fluorescence}} and the {{Corresponding Excited State Dynamics}}},
     booktitle = {Reviews in {{Fluorescence}} 2017},
     author = {Goswami, Debabrata and Das, Dipak Kumar and Makhal, Krishnandu},
     editor = {Geddes, Chris D.},
     date = {2018},
     series = {Reviews in {{Fluorescence}}},
     pages = {145--160},
     publisher = {{Springer International Publishing}},
     location = {{Cham}},
     doi = {10.1007/978-3-030-01569-5_7},
     url = {https://doi.org/10.1007/978-3-030-01569-5_7},
     urldate = {2019-08-01},
     isbn = {978-3-030-01569-5}
   }
   

7. Spectrally Resolved Photon-Echo Spectroscopy of CdSe Quantum Dots at Far from Resonance Excitation Condition. D. Goswami, Journal of Chemical Sciences 130(10), 144 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: Spectrally resolved photon echo spectroscopy in the off-resonance condition is reported for the first time to study the coherence and population dynamics of CdSe quantum dots. In this case, the information related to the system dynamics can be inferred indirectly. This is especially useful when such dynamical information might be hidden under the absorption maxima of the sample. We observe that a substantial intensity of the photon echo signal was obtained in two different CdSe quantum dot samples (CdSe 610 and CdSe 640), which have absorption maxima at 620 nm and 590 nm, respectively. Due to the difference in sizes of these two quantum dots, a small change is observed in the molecular dynamics of these two quantum-dot samples. Specifically, the spectral diffusion of CdSe 640 occurs within the first 50 fs, whereas that for CdSe 610 occurs at about 100 fs timescale. The integrated plots of the photon echo signal, as a function of population time, result in two decay constants. The faster among the two decay components is pulse width limited and is in between 30 and 40 fs at different fixed coherence times for both samples. The slower decay component for the CdSe 610 sample is found to be in the range of 75–85 fs, while that for CdSe 640, it is between 82 and 92 fs at different fixed coherence times.

    BibTeX: @article{goswamiSpectrallyResolvedPhotonecho2018,
     title = {Spectrally Resolved Photon-Echo Spectroscopy of {{CdSe}} Quantum Dots at Far from Resonance Excitation Condition},
     author = {Goswami, Debabrata},
     date = {2018-10},
     journaltitle = {Journal of Chemical Sciences},
     shortjournal = {J Chem Sci},
     volume = {130},
     number = {10},
     pages = {144},
     issn = {0974-3626, 0973-7103},
     doi = {10/gfc5tj},
     url = {https://my.pcloud.com/publink/show?code=XZrGxr7ZCXB5pJHxB4VOKIzAjjEBcmLbB6Gk},
     urldate = {2019-08-01}
   }
   

8. White Light Induced E/Z-Photoisomerization of Diphenylamine-Tethered Fluorescent Stilbene Derivatives: Synthesis, Photophysical, and Electrochemical Investigation. S. Mishra, P. Awasthi, J. Singh, R. K. Gupta, V. Singh, R. Kant, R. Jeet, D. Goswami, and A. Goel, The Journal of Organic Chemistry 83(7), 3669–3678 (2018) [Abstract] [PDF] [BibTeX]

   Abstract: A facile synthesis and detailed photophysical investigation of E/Z-isomerization of fluorescent diphenylamine tethered stilbene derivatives (DPASs) under white light exposure have been carried out to understand the effect on fluorescence, electrochemical properties, and photostability under various activation/deactivation pathways. In solution state, in the dark, the E-isomer of DPASs (6a−d) exhibited high fluorescence quantum yields (Φfl ≈ 53% to 60% in DMSO). However, on white light exposure, 1H NMR and HPLC studies revealed that pure E-isomer of the DPAS 6a (∼9.5 mM) started converting into its Z-form by photoisomerization until it reaches to nearly equilibrium. At low concentrations (∼10 μM), the absorption band of the pure Eisomer in the range of 350−450 nm gradually decreased to adopt Z-conformation 6a′ until a photostationary state was reached. The structure of the E-isomer 6a was unequivocally confirmed by X-ray diffraction analysis. The synthesized DPAS compounds 6a−d possessed positive solvatochromic properties, two photon absorption properties, and good thermal stability. The electrochemical investigations using DPASs showed reversible oxidation resulting in formation of a stable radical cation. Owing to useful photophysical, electrochemical and thermal properties, these DPAS derivatives are suitable for their application in biomedical imaging as well as in fabrication of electroluminescent materials.

    BibTeX: @article{mishraWhiteLightInduced2018,
     title = {White {{Light Induced E}}/{{Z-Photoisomerization}} of {{Diphenylamine-Tethered Fluorescent Stilbene Derivatives}}: {{Synthesis}}, {{Photophysical}}, and {{Electrochemical Investigation}}},
     shorttitle = {White {{Light Induced E}}/{{Z-Photoisomerization}} of {{Diphenylamine-Tethered Fluorescent Stilbene Derivatives}}},
     author = {Mishra, Shachi and Awasthi, Pallavi and Singh, Jagriti and Gupta, Rahul Kumar and Singh, Vikram and Kant, Ruchir and Jeet, Ram and Goswami, Debabrata and Goel, Atul},
     date = {2018-04-06},
     journaltitle = {The Journal of Organic Chemistry},
     shortjournal = {J. Org. Chem.},
     volume = {83},
     number = {7},
     pages = {3669--3678},
     issn = {0022-3263, 1520-6904},
     doi = {10/gc6tzq},
     url = {http://pubs.acs.org/doi/10.1021/acs.joc.8b00033},
     urldate = {2019-08-01}
   }
   

9. Femtosecond Laser-Induced Photothermal Effect for Nanoscale Viscometer and Thermometer. D. Mondal, S. Singhal, and D. Goswami, in Selected Topics in Photonics, A. Pradhan and P. K. Krishnamurthy, eds., IITK Directions (Springer Singapore, 2018), pp. 13–17 [Abstract] [PDF] [BibTeX]

   Abstract: A new method of utilizing photothermal effect at nano-volume dimensions to measure viscosity is presented here that can, in turn, provide the surrounding temperature. Our measurements use high repetition rate, low average power, femtosecond laser pulses that induce photothermal effect that is highly influence by the convective mode of heat transfer. This is especially important for absorbing liquids, which is unlike the typical photothermal effects that are due to such ultrashort pulses. Typical thermal processes involve only conductive mode of heat transfer and are phenomenological in nature. Inclusion of convective mode results in additional molecular characteristics of the thermal process. We measure traditional thermal lens with femtosecond pulse train through geometric beam divergence of a collimated laser beam co-propagating with the focused heating laser beam. The refractive index gradient in the sample arising from a focused heating laser creates a thermal lens, which is measured. On the other hand, the same heat gradient from the focusing heating laser beam generates a change in local viscosity in the medium, which changes the trapped stiffness of an optically trapped microsphere in its vicinity. We use co-propagating femtosecond train of laser pulses at 1560 and 780 nm wavelengths for these experiments. We also show from the bulk thermal studies that use of water as sample has the advantage of using conductive mode of heat transfer for femtosecond pulse train excitation.

    BibTeX: @incollection{mondalFemtosecondLaserInducedPhotothermal2018,
     title = {Femtosecond {{Laser-Induced Photothermal Effect}} for {{Nanoscale Viscometer}} and {{Thermometer}}},
     booktitle = {Selected {{Topics}} in {{Photonics}}},
     author = {Mondal, Dipankar and Singhal, Sumit and Goswami, Debabrata},
     editor = {Pradhan, Asima and Krishnamurthy, Pradeep Kumar},
     date = {2018},
     series = {{{IITK Directions}}},
     pages = {13--17},
     publisher = {{Springer Singapore}},
     location = {{Singapore}},
     doi = {10.1007/978-981-10-5010-7_2},
     url = {https://doi.org/10.1007/978-981-10-5010-7_2},
     urldate = {2019-08-01},
     isbn = {978-981-10-5010-7}
   }
   

10. On-the-Fly Calibrated Measure and Remote Control of Temperature and Viscosity at Nanoscale. D. Mondal, S. N. Bandyopadhyay, P. Mathur, and D. Goswami, ACS Omega 3(9), 12304–12311 (2018) [Abstract] [PDF] [BibTeX]

    Abstract: A novel on-the-f ly calibration method of optical tweezers is presented, which enables in situ control and measure of absolute temperature and viscosity at nanoscale dimensions. Such noncontact measurement and control at the nanoscale are challenging as the present techniques only provide off-line measurements that do not provide absolute values. Additionally, some of the present methods have a low spatial resolution. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The femtosecond optical tweezers (FOTs) use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Such finer temperature gradients are due to the additional nonlinear optical (NLO) phenomena occurring only at the nanoscale focal plane of the FOTs. Because NLO processes are laser peak power-dependent, they promote an effective study of physical properties occurring only at the focal plane. Using FOTs at optically benign near-infrared wavelengths, we demonstrate microrheological control and measurement in water by adding a highly absorbing yet low fluorescent dye (IR780).

     BibTeX: @article{mondalOntheFlyCalibratedMeasure2018,
      title = {On-the-{{Fly Calibrated Measure}} and {{Remote Control}} of {{Temperature}} and {{Viscosity}} at {{Nanoscale}}},
      author = {Mondal, Dipankar and Bandyopadhyay, Soumendra Nath and Mathur, Paresh and Goswami, Debabrata},
      date = {2018-09-30},
      journaltitle = {ACS Omega},
      shortjournal = {ACS Omega},
      volume = {3},
      number = {9},
      pages = {12304--12311},
      issn = {2470-1343, 2470-1343},
      doi = {10/gff5s6},
      url = {http://pubs.acs.org/doi/10.1021/acsomega.8b01572},
      urldate = {2019-08-01}
    }
    

11. Deciphering Micro-Polarity inside the Endoplasmic Reticulum Using a Two-Photon Active Solvatofluorochromic Probe. K. Pal, I. Samanta, R. Kumar Gupta, D. Goswami, and A. Lal Koner, Chemical Communications 54(75), 10590–10593 (2018) [PDF] [BibTeX]

     BibTeX: @article{palDecipheringMicropolarityEndoplasmic2018,
      title = {Deciphering Micro-Polarity inside the Endoplasmic Reticulum Using a Two-Photon Active Solvatofluorochromic Probe},
      author = {Pal, Kaushik and Samanta, Indranil and Kumar~Gupta, Rahul and Goswami, Debabrata and Lal~Koner, Apurba},
      date = {2018},
      journaltitle = {Chemical Communications},
      volume = {54},
      number = {75},
      pages = {10590--10593},
      doi = {10/gf5mqx},
      url = {https://pubs.rsc.org/en/content/articlelanding/2018/cc/c8cc03962c},
      urldate = {2019-08-01}
    }
    

2017

1. Meet OSA’s 2017 Fellows. K. Apter, M. Smith, and Z. Epps, Optics and Photonics News 28(2), 38–47 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: The 96 members of the 2017 class of OSA Fellow Members will be recognized at conferences throughout the year for scientific, engineering, educational and technological contributions, as well as service and business leadership.

    BibTeX: @article{apterMeetOSA20172017,
     title = {Meet {{OSA}}’s 2017 {{Fellows}}},
     author = {Apter, Kari and Smith, Meredith and Epps, Zsanai},
     date = {2017-02-01},
     journaltitle = {Optics and Photonics News},
     shortjournal = {Optics \& Photonics News, OPN},
     volume = {28},
     number = {2},
     pages = {38--47},
     issn = {1541-3721},
     doi = {10/gf5mrj},
     url = {https://my.pcloud.com/publink/show?code=XZqaxr7ZmnVNxAn4Y4mRbGS3d4A7FjmCWEv7},
     urldate = {2019-08-01}
   }
   

2. Two-Dimensional Imaging of a Second-Order Nonlinear Optical Process. I. Bhattacharyya and D. Goswami, Current Science 112(04), 830 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: Spatiotemporal imaging of sum-frequency generation process through second-order nonlinear optical interaction in a nonlinear crystal under femtosecond pulsed illumination is presented. Two focal points in the spatial dimension that result from use of widely separated wavelengths (780 and 1560 nm) including their appropriate intensity ratios are captured accurately, emphasizing the sensitivity and robustness of this detection scheme. Most importantly, crosscorrelation width that is used as characteristic measure from such techniques remains constant at the two focal points. However, this highlights the critical role of nonlinear crystal position along beam propagation axis during such collinear intensity cross-correlation measurements involving different wavelengths.

    BibTeX: @article{bhattacharyyaTwoDimensionalImagingSecondOrder2017,
     title = {Two-{{Dimensional Imaging}} of a {{Second-Order Nonlinear Optical Process}}},
     author = {Bhattacharyya, Indrajit and Goswami, Debabrata},
     date = {2017-02-01},
     journaltitle = {Current Science},
     volume = {112},
     number = {04},
     pages = {830},
     issn = {0011-3891},
     doi = {10/f92q98},
     url = {http://pc.cd/mxLctalK},
     urldate = {2019-08-01}
   }
   

3. Structured Interferometry Features in Femtosecond Supercontinuum: Towards Better Understanding of Supercontinuum for Bio Applications. D. Goswami, S. Dinda, and S. N. Bandyopadhyay, in Optical Biopsy XV: Toward Real-Time Spectroscopic Imaging and Diagnosis (International Society for Optics and Photonics, 2017), 10060, p. 1006019 [Abstract] [PDF] [BibTeX]

   Abstract: We report structured interferometry features in femtosecond supercontinuum generated with power near to supercontinuum generation threshold. We argue that these structures arise from the coherent superposition of supercontinuum generated from different sources of supercontinuum as pulse split into two daughter pulses. Increase in input pulse energy creates several more temporal pulse fragments and disrupts interference resulting in the typical feature of continuous broad supercontinuum. Such an understanding of supercontinuum generation process is critical to the use of supercontinuum as the light source for use in understanding the time dynamics and imaging of bio systems.

    BibTeX: @inproceedings{goswamiStructuredInterferometryFeatures2017,
     title = {Structured Interferometry Features in Femtosecond Supercontinuum: Towards Better Understanding of Supercontinuum for Bio Applications},
     shorttitle = {Structured Interferometry Features in Femtosecond Supercontinuum},
     booktitle = {Optical {{Biopsy XV}}: {{Toward Real-Time Spectroscopic Imaging}} and {{Diagnosis}}},
     author = {Goswami, Debabrata and Dinda, Sirshendu and Bandyopadhyay, Soumendra N.},
     date = {2017-02-17},
     volume = {10060},
     pages = {1006019},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/gf5mrd},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10060/1006019/Structured-interferometry-features-in-femtosecond-supercontinuum--towards-better-understanding/10.1117/12.2253561.short},
     urldate = {2019-08-01},
     eventtitle = {Optical {{Biopsy XV}}: {{Toward Real-Time Spectroscopic Imaging}} and {{Diagnosis}}}
   }
   

4. Extracting Third Order Optical Nonlinearities of Mn(III)-Phthalocyanine Chloride Using High Repetition Rate Femtosecond Pulses. K. Makhal, P. Mathur, S. Maurya, and D. Goswami, Journal of Applied Physics 121(5), 053103 (2017) [PDF] [BibTeX]

    BibTeX: @article{makhalExtractingThirdOrder2017,
     title = {Extracting Third Order Optical Nonlinearities of {{Mn}}({{III}})-{{Phthalocyanine}} Chloride Using High Repetition Rate Femtosecond Pulses},
     author = {Makhal, Krishnandu and Mathur, Paresh and Maurya, Sidharth and Goswami, Debabrata},
     date = {2017-02-06},
     journaltitle = {Journal of Applied Physics},
     shortjournal = {Journal of Applied Physics},
     volume = {121},
     number = {5},
     pages = {053103},
     issn = {0021-8979},
     doi = {10/gf5mrh},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.4974966},
     urldate = {2019-08-01}
   }
   

5. pH Effect on Two-Photon Cross Section of Highly Fluorescent Dyes Using Femtosecond Two-Photon Induced Fluorescence. K. Makhal and D. Goswami, Journal of Fluorescence 27(1), 339–356 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: Effect of solution pH on two-photon absorption cross-section of highly fluorescent Coumarin and Rhodamine dyes with high repetition rate femtosecond laser pulses at 780 nm is presented using two-photon induced fluorescence technique. A correspondence in the measured two-photon and single-photon cross-section values is seen when the pH changes from acidic to basic conditions (pH = 2–10) for solutions in 1:1 water-ethanol binary mixture. By plotting changes in the single-photon and two-photon fluorescence in this pH range, the excited state pKa values are found. The ground state pKa values are also affected by the protonation deprotonation equilibrium as a result of variation in pH from acidic to basic, which are characterized by changes in absorbance spectra. Most of these single-photon and two-photon induced fluorescence spectra show characteristic blue shifts. Different fluorescence quantum yields calculated at each pH reflect a change in structure corresponding to their associated properties as a result of acid base equilibrium.

    BibTeX: @article{makhalPHEffectTwoPhoton2017,
     title = {{{pH Effect}} on {{Two-Photon Cross Section}} of {{Highly Fluorescent Dyes Using Femtosecond Two-Photon Induced Fluorescence}}},
     author = {Makhal, Krishnandu and Goswami, Debabrata},
     date = {2017-01-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {27},
     number = {1},
     pages = {339--356},
     issn = {1573-4994},
     doi = {10/f9rpw6},
     url = {https://doi.org/10.1007/s10895-016-1963-4},
     urldate = {2019-08-01}
   }
   

6. Concentration Dependent Approach for Accurate Determination of Two-Photon Absorption Cross-Section of Fluorescent Dye Molecule. S. K. Maurya, C. Dutta, and D. Goswami, Journal of Fluorescence 27(4), 1399–1403 (2017) [Abstract] [PDF] [BibTeX]

   Abstract: We have investigated the concentration dependent of two-photon induced fluorescence (TPIF) in methanolic solution of Rhodamine 6G and Rhodamine B dye using 120 fs laser pulses at 780 nm, 76 MHz repetition rate. TPIF study of these dyes was compared with their respective one photon fluorescence intensity. We have shown the effect of chopper on TPIF intensity from Rhodamine dyes, which have shown direct influence on the determined TPA Cross section of these dyes.

    BibTeX: @article{mauryaConcentrationDependentApproach2017,
     title = {Concentration {{Dependent Approach}} for {{Accurate Determination}} of {{Two-Photon Absorption Cross-Section}} of {{Fluorescent}} Dye {{Molecule}}},
     author = {Maurya, Sandeep Kumar and Dutta, Chayan and Goswami, Debabrata},
     date = {2017-07-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {27},
     number = {4},
     pages = {1399--1403},
     issn = {1573-4994},
     doi = {10/gf5mq7},
     url = {https://doi.org/10.1007/s10895-017-2076-4},
     urldate = {2019-08-01}
   }
   

7. Microrheology Study of Aqueous Suspensions of Laponite Using Femtosecond Optical Tweezers. D. Mondal, A. Jha, Y. M. Joshi, and D. Goswami, in Optics in the Life Sciences Congress (2017), Paper OtW2E.1 (Optical Society of America, 2017), p. OtW2E.1 [Abstract] [PDF] [BibTeX]

   Abstract: We have observed microrheological aging dynamics of Laponite® suspensions using femtosecond optical tweezers (FOTs). Our on the fly calibration in time domain has been used to probe microscopic structural changes in the complex fluid.

    BibTeX: @inproceedings{mondalMicrorheologyStudyAqueous2017,
     title = {Microrheology {{Study}} of {{Aqueous Suspensions}} of {{Laponite}} Using {{Femtosecond Optical Tweezers}}},
     booktitle = {Optics in the {{Life Sciences Congress}} (2017), Paper {{OtW2E}}.1},
     author = {Mondal, Dipankar and Jha, Anushka and Joshi, Yogesh M. and Goswami, Debabrata},
     date = {2017-04-02},
     pages = {OtW2E.1},
     publisher = {{Optical Society of America}},
     doi = {10/gf5mrb},
     url = {https://www.osapublishing.org/abstract.cfm?uri=OTA-2017-OtW2E.1},
     urldate = {2019-08-01},
     eventtitle = {Optical {{Trapping Applications}}}
   }
   

8. In Situ Temperature Control and Measurement with Femtosecond Optical Tweezers: Offering Biomedical Application. D. Mondal and D. Goswami, in Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues XV (International Society for Optics and Photonics, 2017), 10068, p. 100681T [Abstract] [PDF] [BibTeX]

   Abstract: We present here the control and measurement of temperature rise using femtosecond optical tweezers at near infrared (NIR) region. Based on our theoretical development, we have designed our experimental techniques. The high temporal sensitivity of position autocorrelation and equipartition theorem is simultaneously applied to elucidate temperature control and high precision measurement around focal volume. Experimentally we have made the benign NIR wavelength to induce local heating by adding very low fluorescent dye molecule with low average power. Local temperature control in aqueous solution exciting within optically absorbing window of the low quantum yield molecules can be possible due to non-radiative relaxation via thermal emission. The stochastic nature of Brownian particle has enough information of its surroundings. We have mapped the nano-dimension beam waist environment by probing the fluctuation of trapped particle. We have observed up to 30K temperature rise from room temperature at sub micro molar concentration. The gradient of temperature is as sharp as the fluence of pulsed laser focused by high numerical aperture objective. Thus, pulsed laser radiation always allows finer surgical techniques involving minimal thermal injuries. Our new techniques with multiphoton absorbing non-fluorescent dye can further be used to selective phototherapeutic diagnosis of cancer cells due to peak power dependent nonlinear phenomenon (NLO).

    BibTeX: @inproceedings{mondalSituTemperatureControl2017,
     title = {In Situ Temperature Control and Measurement with Femtosecond Optical Tweezers: Offering Biomedical Application},
     shorttitle = {In Situ Temperature Control and Measurement with Femtosecond Optical Tweezers},
     booktitle = {Imaging, {{Manipulation}}, and {{Analysis}} of {{Biomolecules}}, {{Cells}}, and {{Tissues XV}}},
     author = {Mondal, Dipankar and Goswami, Debabrata},
     date = {2017-02-16},
     volume = {10068},
     pages = {100681T},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/gf5mrg},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10068/100681T/In-situ-temperature-control-and-measurement-with-femtosecond-optical-tweezers/10.1117/12.2251892.short},
     urldate = {2019-08-01},
     eventtitle = {Imaging, {{Manipulation}}, and {{Analysis}} of {{Biomolecules}}, {{Cells}}, and {{Tissues XV}}}
   }
   

9. Measurement of Pure Optical Nonlinearity in Carbon Disulfide with a High-Repetition-Rate Femtosecond Laser. S. Singhal, S. Dinda, and D. Goswami, Applied Optics 56(3), 644 (2017) [PDF] [BibTeX]

    BibTeX: @article{singhalMeasurementPureOptical2017,
     title = {Measurement of Pure Optical Nonlinearity in Carbon Disulfide with a High-Repetition-Rate Femtosecond Laser},
     author = {Singhal, Sumit and Dinda, Sirshendu and Goswami, Debabrata},
     date = {2017-01-20},
     journaltitle = {Applied Optics},
     shortjournal = {Appl. Opt.},
     volume = {56},
     number = {3},
     pages = {644},
     issn = {0003-6935, 1539-4522},
     doi = {10/gf5mrm},
     url = {https://www.osapublishing.org/abstract.cfm?URI=ao-56-3-644},
     urldate = {2019-08-01}
   }
   

10. A Dual-Signaling Ferrocene-Pyrene Dyad: Triple-Mode Recognition of the Cu(II) Ions in Aqueous Medium. M. A. Wani, M. D. Pandey, R. Pandey, S. K. Maurya, and D. Goswami, Journal of Fluorescence 27(6), 2279–2286 (2017) [Abstract] [PDF] [BibTeX]

    Abstract: We report a structure of ferrocene-pyrene conjugate (1) comprising electro and photo-active dual-signaling units. In particular, 1 upon interaction with Cu(II), displays selectively one-photon fluorescence quenching, but it shows two-photon absorption (TPA) cross-section 1230 GM (at 780 nm). Further, 1 displayed two irreversible oxidative waves at 0.39 V and 0.80 V (vs Ag/AgCl), in the electrochemical analysis which upon addition of Cu2+, led to the negative potential shift in both the oxidative waves to appear at 0.25 V and 0.68 V. The triple mode changes in presence of Cu(II) suggesting the possible application of 1 for the detection of Cu(II) in aqueous media. Open image in new window Graphical Abstract

     BibTeX: @article{waniDualSignalingFerrocenePyreneDyad2017,
      title = {A {{Dual-Signaling Ferrocene-Pyrene Dyad}}: {{Triple-Mode Recognition}} of the {{Cu}}({{II}}) {{Ions}} in {{Aqueous Medium}}},
      shorttitle = {A {{Dual-Signaling Ferrocene-Pyrene Dyad}}},
      author = {Wani, Manzoor Ahmad and Pandey, Mrituanjay D. and Pandey, Rampal and Maurya, Sandeep Kumar and Goswami, Debabrata},
      date = {2017-11-01},
      journaltitle = {Journal of Fluorescence},
      shortjournal = {J Fluoresc},
      volume = {27},
      number = {6},
      pages = {2279--2286},
      issn = {1573-4994},
      doi = {10/gch5h7},
      url = {https://doi.org/10.1007/s10895-017-2169-0},
      urldate = {2019-08-01}
    }
    

2016

1. Direct Observation of Diatoms Pair Formation in Aqueous Solution Under Laser Scanning Fluorescence Microscopy. D. Das and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. Tu2B.3 [Abstract] [PDF] [BibTeX]

   Abstract: We show important applications of our imaging technique in visualizing the morphology as well as division of diatoms in aqueous solution. The technique involves the efficient detection of the auto-fluorescence from chloroplast and shell structure through laser scanning confocal microscopy.

    BibTeX: @inproceedings{dasDirectObservationDiatoms2016,
     title = {Direct {{Observation}} of {{Diatoms Pair Formation}} in {{Aqueous Solution Under Laser Scanning Fluorescence Microscopy}}},
     booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Das, Dhiman and Goswami, Debabrata},
     date = {2016},
     pages = {Tu2B.3},
     publisher = {{OSA}},
     location = {{Kharagpur}},
     doi = {10/gf5mrq},
     url = {https://my.pcloud.com/publink/show?code=XZrNxr7ZTM0YMQbaakBFrDr1GOUzFXGBIn6V},
     urldate = {2019-08-01},
     eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
     isbn = {978-1-943580-22-4}
   }
   

2. Spatiotemporal Control of Degenerate Multiphoton Fluorescence Microscopy with Delay-Tunable Femtosecond Pulse Pairs. D. Das, I. Bhattacharyya, and D. Goswami, Chemical Physics Letters 657, 72–77 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Selective excitation of a particular fluorophore in an ensemble of different fluorophores with overlapping fluorescence spectra is shown to be dependent on the time delay of femtosecond pulse pairs in multiphoton fluorescence microscopy. In particular, the two-photon fluorescence behavior of the Texas Red and DAPI dye pair inside Bovine Pulmonary Artery Endothelial (BPAE) cells depends strongly on the center wavelength of the laser, as well as the delay between two identical laser pulses in one-color femtosecond pulse-pair excitation scheme. Thus, we present a novel design concept using pairs of femtosecond pulses at different central wavelengths and tunable pulse separations for controlling the image contrast between two spatially and spectrally overlapping fluorophores. This femtosecond pulse-pair technique is unique in utilizing the variation of dye dynamics inside biological cells as a contrast mode in microscopy of different fluorophores.

    BibTeX: @article{dasSpatiotemporalControlDegenerate2016,
     title = {Spatiotemporal Control of Degenerate Multiphoton Fluorescence Microscopy with Delay-Tunable Femtosecond Pulse Pairs},
     author = {Das, Dhiman and Bhattacharyya, Indrajit and Goswami, Debabrata},
     date = {2016-07-16},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {657},
     pages = {72--77},
     issn = {0009-2614},
     doi = {10/f84rwd},
     url = {https://my.pcloud.com/publink/show?code=XZ1Axr7ZxiTGNbfEV1bmLPqho9PtQzSq3qUk},
     urldate = {2019-08-01}
   }
   

3. On the Interferometric Coherent Structures in Femtosecond Supercontinuum Generation. S. Dinda, S. N. Bandyopadhyay, and D. Goswami, Applied Physics B 122(5), 148 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: We report structured interferometric features in femtosecond supercontinuum generation (FSG) with incident laser powers that are near threshold for FSG. We argue that near threshold, these structures arise from the coherent superposition of pulses that are split initially into two daughter pulses during FSG process. Increase in the input pulse energy generates multiple daughter fragments in the temporal domain to an extent that correlated interference structures are not measurable.

    BibTeX: @article{dindaInterferometricCoherentStructures2016,
     title = {On the Interferometric Coherent Structures in Femtosecond Supercontinuum Generation},
     author = {Dinda, Sirshendu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2016-05-11},
     journaltitle = {Applied Physics B},
     shortjournal = {Appl. Phys. B},
     volume = {122},
     number = {5},
     pages = {148},
     issn = {1432-0649},
     doi = {10/gf5mr5},
     url = {https://my.pcloud.com/publink/show?code=XZfaxr7ZhXTWojTzmcfBOA16JDESUyR5fRWV},
     urldate = {2019-08-01}
   }
   

4. Quantum Distributed Computing with Shaped Laser Pulses. R. Goswami and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. W4C.3 [Abstract] [BibTeX]

   Abstract: Shaped laser pulses can control decoherence under quantum adiabatic method of logic operations to result in a possible scalable quantum computer by distributing the computing load on a set of optically adiabatic quantum computing nodes.

    BibTeX: @inproceedings{goswamiQuantumDistributedComputing2016,
     title = {Quantum {{Distributed Computing}} with {{Shaped Laser Pulses}}},
     booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Goswami, Rohit and Goswami, Debabrata},
     date = {2016},
     pages = {W4C.3},
     publisher = {{OSA}},
     location = {{Kanpur}},
     doi = {10/gf5mrr},
     eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
     isbn = {978-1-943580-22-4}
   }
   

5. Optical Trapping Dynamics of a Single Polystyrene Sphere: Continuous Wave versus Femtosecond Lasers. T.-H. Liu, W.-Y. Chiang, A. Usman, and H. Masuhara, The Journal of Physical Chemistry C 120(4), 2392–2399 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Understanding of optical trapping dynamics of a single particle in the trapping site is important to develop its optical manipulation for molecular assembly and chemical application. For micrometer-sized Mie particles, similar trapping efficiency of the conventional continuous wave (cw) laser or high-repetition-rate femtosecond (fs) laser pulse train has been established [Dholakia et al., Opt. Express 2010, 18, 7554–7568], in contrast to higher efficiency of the laser pulses to trap dielectric Rayleigh particles. To further explore and clarify the switching phenomena of optical trapping efficiency with cw laser and fs laser pulse and to elucidate its nature, we study the immobilization dynamics of a single polystyrene sphere with 500 nm in diameter (which is comparable to focal beam size) in shallow potential well. By observing trapping events and immobilization time of the particle with a size in Lorenz–Mie regime, distinct from well-known Rayleigh particle and ray optics approximations, we found that immobilization time is only linearly related to the incident laser power ≤40 mW, and at higher laser powers cw laser is more efficient than fs laser pulses to immobilize the particle. This finding means that the dynamics of the particle in this size region is still affected by the strong transient force fields induced by high-repetition-rate ultrashort pulse train as usually observed for Rayleigh particles. This may provide an understanding that the dynamics of the target particle in the trapping site is size- and laser mode-dependent.

    BibTeX: @article{liuOpticalTrappingDynamics2016,
     title = {Optical {{Trapping Dynamics}} of a {{Single Polystyrene Sphere}}: {{Continuous Wave}} versus {{Femtosecond Lasers}}},
     shorttitle = {Optical {{Trapping Dynamics}} of a {{Single Polystyrene Sphere}}},
     author = {Liu, Tsung-Han and Chiang, Wei-Yi and Usman, Anwar and Masuhara, Hiroshi},
     date = {2016-02-04},
     journaltitle = {The Journal of Physical Chemistry C},
     shortjournal = {J. Phys. Chem. C},
     volume = {120},
     number = {4},
     pages = {2392--2399},
     issn = {1932-7447},
     doi = {10/gf85zr},
     url = {https://doi.org/10.1021/acs.jpcc.5b09146},
     urldate = {2019-10-01}
   }
   

6. Reverse Saturable Absorption Followed by Anomalous Saturable Absorption in Rhodamine-700. K. Makhal, S. Maurya, and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. Tu5D.2 [Abstract] [PDF] [BibTeX]

   Abstract: Anomalous SA (saturable absorption) in presence of reverse saturable absorption (RSA) in Rhodamine-700 is reported employing Z-scan with 100 ns, 250 Hz pulses in methanol. SA is observed only at a particular intensity range otherwise RSA survives.

    BibTeX: @inproceedings{makhalReverseSaturableAbsorption2016,
     title = {Reverse {{Saturable Absorption}} Followed by {{Anomalous Saturable Absorption}} in {{Rhodamine-700}}},
     booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Makhal, Krishnandu and Maurya, Sidharth and Goswami, Debabrata},
     date = {2016},
     pages = {Tu5D.2},
     publisher = {{OSA}},
     location = {{Kharagpur}},
     doi = {10/gf5mrp},
     url = {https://www.osapublishing.org/abstract.cfm?URI=Photonics-2016-Tu5D.2},
     urldate = {2019-08-01},
     eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
     isbn = {978-1-943580-22-4}
   }
   

7. Third-Order Nonlinear Optical Response and Ultrafast Dynamics of Tetraoxa[22]Porphyrin(2.1.2.1)s. K. Makhal, S. Arora, P. Kaur, D. Goswami, and K. Singh, Journal of Materials Chemistry C 4(40), 9445–9453 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast dynamics and third-order nonlinear optical studies of tetraoxa[22]porphyrin(2.1.2.1)s are reported using a single beam Z-scan technique with femtosecond (fs) and nanosecond (ns) pulses at respective near-IR and visible wavelengths. Excited state absorption mediated reverse saturable absorption was observed at 527 nm while two-photon absorption was observed at 800 nm. High nonlinear refractive index coefficient (γ) and nonlinear absorption coefficient (β) values and the fast response times were attributed to the availability of polarizable π-electrons of the cyclic conjugated aromatic porphyrin framework. Our proposed mechanism of third-order nonlinearity was verified using ultrafast transient absorption spectroscopy. With the observed fast electronic nonlinearities the studied molecules are potential candidates for use as optical limiters.

    BibTeX: @article{makhalThirdorderNonlinearOptical2016,
     title = {Third-Order Nonlinear Optical Response and Ultrafast Dynamics of Tetraoxa[22]Porphyrin(2.1.2.1)s},
     author = {Makhal, Krishnandu and Arora, Shafali and Kaur, Paramjit and Goswami, Debabrata and Singh, Kamaljit},
     date = {2016},
     journaltitle = {Journal of Materials Chemistry C},
     volume = {4},
     number = {40},
     pages = {9445--9453},
     doi = {10/gf5mr7},
     url = {https://pubs.rsc.org/en/content/articlelanding/2016/tc/c6tc03239g},
     urldate = {2019-08-01}
   }
   

8. Investigating Two-Photon-Induced Fluorescence in Rhodamine-6G in Presence of Cetyl-Trimethyl-Ammonium-Bromide. S. K. Maurya, D. Yadav, and D. Goswami, Journal of Fluorescence 26(5), 1573–1577 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: We investigate the effect of cetyl-trimethyl-ammonium-bromides (CTAB) concentration on the fluorescence of Rhodamine-6G in water. This spectroscopic study of Rhodamine-6G in presence of CTAB was performed using two-photon-induced-fluorescence at 780 nm wavelength using high repetition rate femtosecond laser pulses. We report an increment of ∼10 % in the fluorescence in accordance with ∼12 % enhancement in the absorption intensity of the dye molecule around the critical micellar concentration. We discuss the possible mechanism for the enhancement in the two-photon fluorescence intensity and the importance of critical micellar concentration.

    BibTeX: @article{mauryaInvestigatingTwoPhotonInducedFluorescence2016,
     title = {Investigating {{Two-Photon-Induced Fluorescence}} in {{Rhodamine-6G}} in {{Presence}} of {{Cetyl-Trimethyl-Ammonium-Bromide}}},
     author = {Maurya, Sandeep Kumar and Yadav, Dheerendra and Goswami, Debabrata},
     date = {2016-09-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {26},
     number = {5},
     pages = {1573--1577},
     issn = {1573-4994},
     doi = {10/f82q4x},
     url = {https://doi.org/10.1007/s10895-016-1841-0},
     urldate = {2019-08-01}
   }
   

9. Probing Intermolecular Interactions in Binary Liquid Mixtures Using Femtosecond Laser-Induced Self-Defocusing. S. K. Maurya, D. Das, and D. Goswami, Applied Spectroscopy 70(10), 1655–1661 (2016) [Abstract] [PDF] [BibTeX]

   Abstract: Photothermal behavior of binary liquid mixtures has been studied using a high repetition rate (HRR) Z-scan technique with femtosecond laser pulses. Changes in the peak–valley difference in transmittance (ΔTP–V) for closed aperture Z-scan experiments are indicative of thermal effects induced by HRR femtosecond laser pulses. We show such indicative results can have a far-reaching impact on molecular properties and intermolecular interactions in binary liquid mixtures. Spectroscopic parameters derived from this experimental technique show that the combined effect of physical and molecular properties of the constituent binary liquids can be related to the components of the binary liquid.

    BibTeX: @article{mauryaProbingIntermolecularInteractions2016,
     title = {Probing {{Intermolecular Interactions}} in {{Binary Liquid Mixtures Using Femtosecond Laser-Induced Self-Defocusing}}},
     author = {Maurya, Sandeep Kumar and Das, Dhiman and Goswami, Debabrata},
     date = {2016-10-01},
     journaltitle = {Applied Spectroscopy},
     shortjournal = {Appl Spectrosc},
     volume = {70},
     number = {10},
     pages = {1655--1661},
     issn = {0003-7028},
     doi = {10/gf5mrx},
     url = {https://doi.org/10.1177/0003702816643547},
     urldate = {2019-08-01}
   }
   

10. Controlling and Tracking of Colloidal Nanostructures through Two-Photon Fluorescence. D. Mondal and D. Goswami, Methods and Applications in Fluorescence 4(4), 044004 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: Multiphoton absorbing dye-coated trapped spherical bead at the focal plane of femtosecond optical tweezers shows nonlinear optical (NLO) phenomena. One such NLO process of two-photon fluorescence (TPF) has been used for the background-free imaging of a femtosecond laser-trapping event. Due to the high peak powers of femtosecond laser pulses with low average powers, it is possible to not only trap single nanospheres, but encourage optically directed self-assembly. The TPF signatures of trapped particles show evidence of such a directed self-assembly process which, in turn, can provide information about the structural dynamics during the process of cluster formation. We are able to trap and characterize structure and dynamics in 3D until pentamer formation from the decay characteristics of trapping at the focal plane.

     BibTeX: @article{mondalControllingTrackingColloidal2016,
      title = {Controlling and Tracking of Colloidal Nanostructures through Two-Photon Fluorescence},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-10-07},
      journaltitle = {Methods and Applications in Fluorescence},
      shortjournal = {Methods Appl. Fluoresc.},
      volume = {4},
      number = {4},
      pages = {044004},
      issn = {2050-6120},
      doi = {10/gf5mrw},
      url = {http://stacks.iop.org/2050-6120/4/i=4/a=044004?key=crossref.b299c380a1fd88f37b79e579221d3e7a},
      urldate = {2019-08-01}
    }
    

11. Elucidating Two Photon FRET and Its Application through Femtosecond Optical Tweezers. D. Mondal, D. Roy, S. Dinda, A. Singh, and D. Goswami, in Advanced Photonics 2016 (IPR, NOMA, Sensors, Networks, SPPCom, SOF) (OSA, 2016), p. NoTu2D.4 [Abstract] [PDF] [BibTeX]

    Abstract: We have observed two photon fluorescence resonance energy transfer (FRET) from optically trapped bead coated with multiple dyes. The fluorescence obtained from trapped particles is useful to measure biomechanical property of that confined system.

     BibTeX: @inproceedings{mondalElucidatingTwoPhoton2016,
      title = {Elucidating {{Two Photon FRET}} and Its Application through Femtosecond Optical Tweezers},
      booktitle = {Advanced {{Photonics}} 2016 ({{IPR}}, {{NOMA}}, {{Sensors}}, {{Networks}}, {{SPPCom}}, {{SOF}})},
      author = {Mondal, Dipankar and Roy, Debjit and Dinda, Sirshendu and Singh, Ajitesh and Goswami, Debabrata},
      date = {2016},
      pages = {NoTu2D.4},
      publisher = {{OSA}},
      location = {{Vancouver}},
      doi = {10/gf5mr4},
      url = {https://www.osapublishing.org/abstract.cfm?URI=NOMA-2016-NoTu2D.4},
      urldate = {2019-08-01},
      eventtitle = {Novel {{Optical Materials}} and {{Applications}}},
      isbn = {978-1-943580-14-9}
    }
    

12. Femtosecond Optical Tweezers as Sensitive Nano-Thermometer. D. Mondal and D. Goswami, in Frontiers in Optics 2016 (OSA, 2016), p. JTh2A.117 [Abstract] [PDF] [BibTeX]

    Abstract: Nano-volume temperature rise around optical trap is measured by exploiting non radiative relaxation in solvents. Co-propagating 1560 nm femtosecond laser pulses change solvent temperature and viscosity while trap-stiffness is unaffected during 780 nm trapping.

     BibTeX: @inproceedings{mondalFemtosecondOpticalTweezers2016,
      title = {Femtosecond Optical Tweezers as Sensitive Nano-Thermometer},
      booktitle = {Frontiers in {{Optics}} 2016},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016},
      pages = {JTh2A.117},
      publisher = {{OSA}},
      location = {{Rochester, New York}},
      doi = {10/gf5mrv},
      url = {https://www.osapublishing.org/abstract.cfm?URI=FiO-2016-JTh2A.117},
      urldate = {2019-08-01},
      eventtitle = {Frontiers in {{Optics}}},
      isbn = {978-1-943580-19-4}
    }
    

13. Precise Control and Measurement of Temperature with Femtosecond Optical Tweezers. D. Mondal and D. Goswami, Biophysical Journal 110(3), 500a (2016) [Abstract] [PDF] [BibTeX]

    Abstract: Optical traps have often been used for physical manipulation and transport within liquids for studying bio-systems. In this connection, though a lot of work has focused on the property of the trapped particle, there is little effort on utilizing the effect of the trapping environment. Here we demonstrate a novel method for exploiting the effect of trapping environment in observing the temperature rise in liquids directly at the vicinity of an optical trap center. Our approach utilizes the photo-thermal effect at micro-volume dimension to measure temperature, which could eventually be extended to in-vivo conditions. Our two-color experiment is a unique combination of a non-heating femtosecond trapping laser at 780 nm, which is coupled to a femtosecond infrared heating laser at 1560 nm. Femtosecond pulsed laser heating is much more effective than the traditional continuous-wave laser, which increases the sensitivity of our measurements. The heating laser precisely controls temperature at the focal volume of the trap center using low powers at high repetition rate. The changed values of corner frequency of the optical trap due to this local heating is recognized from its power spectra. The solvent having hydroxyl group is very sensitive to 1560 nm laser due to non-radiative relaxation from their higher excited state. Since most bio-systems contain hydroxyl group, they would be highly responsive to our heating laser, while our trapping laser is highly transparent for such systems. Our method could be used to specifically heat a particular cell to evaluate its faster cell division and also can be utilized for the possible phototherapy of cancer cells. The advantage of this technique over the conventional phototherapy is that this is highly localized due to focusing through high numerical aperture resulting in a high gradient of temperature.

     BibTeX: @article{mondalPreciseControlMeasurement2016,
      title = {Precise {{Control}} and {{Measurement}} of {{Temperature}} with {{Femtosecond Optical Tweezers}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-02},
      journaltitle = {Biophysical Journal},
      shortjournal = {Biophysical Journal},
      volume = {110},
      number = {3},
      pages = {500a},
      issn = {00063495},
      doi = {10/gf5mr6},
      url = {https://linkinghub.elsevier.com/retrieve/pii/S0006349515038564},
      urldate = {2019-08-01}
    }
    

14. Precise Control and Measurement of Solid–Liquid Interfacial Temperature and Viscosity Using Dual-Beam Femtosecond Optical Tweezers in the Condensed Phase. D. Mondal, P. Mathur, and D. Goswami, Physical Chemistry Chemical Physics 18(37), 25823–25830 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: We present a novel method of microrheology based on femtosecond optical tweezers, which in turn enables us to directly measure and control in situ temperature at microscale volumes at the solid–liquid interface. A noninvasive pulsed 780 nm trapped bead spontaneously responds to changes in its environment induced by a co-propagating 1560 nm pulsed laser due to mutual energy transfer between the solvent molecules and the trapped bead. Strong absorption of the hydroxyl group by the 1560 nm laser creates local heating in individual and binary mixtures of water and alcohols. “Hot Brownian motion” of the trapped polystyrene bead is reflected in the corner frequency deduced from the power spectrum. Changes in corner frequency values enable us to calculate the viscosity as well as temperature at the solid–liquid interface. We show that these experimental results can also be theoretically ratified.

     BibTeX: @article{mondalPreciseControlMeasurement2016a,
      title = {Precise Control and Measurement of Solid–Liquid Interfacial Temperature and Viscosity Using Dual-Beam Femtosecond Optical Tweezers in the Condensed Phase},
      author = {Mondal, Dipankar and Mathur, Paresh and Goswami, Debabrata},
      date = {2016},
      journaltitle = {Physical Chemistry Chemical Physics},
      volume = {18},
      number = {37},
      pages = {25823--25830},
      doi = {10/gf5mr8},
      url = {https://pubs.rsc.org/en/content/articlelanding/2016/cp/c6cp03093a},
      urldate = {2019-08-01}
    }
    

15. Sensitive in Situ Nanothermometer Using Femtosecond Optical Tweezers. D. Mondal and D. Goswami, Journal of Nanophotonics 10(2), 026013 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: We report the rise in temperature in various liquid media adjacent to a trapped bead. A nonheating laser at 780 nm has been used to optically trap a 500-nm radius polystyrene bead, while a simultaneous irradiation with a copropagating 1560-nm high-repetition-rate femtosecond laser led to temperature rise in various trapping media. Vibrational combination band of the hydroxyl group in the trapping media resulted in high absorption of 1560-nm laser. This, in turn, gave us control over the trapping media temperature at the focus of the optical trap.

     BibTeX: @article{mondalSensitiveSituNanothermometer2016,
      title = {Sensitive in Situ Nanothermometer Using Femtosecond Optical Tweezers},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-05},
      journaltitle = {Journal of Nanophotonics},
      shortjournal = {JNP},
      volume = {10},
      number = {2},
      pages = {026013},
      issn = {1934-2608, 1934-2608},
      doi = {10/f832c9},
      url = {https://www.spiedigitallibrary.org/journals/Journal-of-Nanophotonics/volume-10/issue-2/026013/----Custom-HTML----Sensitive/10.1117/1.JNP.10.026013.short},
      urldate = {2019-08-01}
    }
    

16. Temperature Control and Measurement with Tunable Femtosecond Optical Tweezers. D. Mondal and D. Goswami, in Optical Trapping and Optical Micromanipulation XIII (International Society for Optics and Photonics, 2016), 9922, p. 992210 [Abstract] [PDF] [BibTeX]

    Abstract: We present the effects of wavelength dependent temperature rise in a femtosecond optical tweezers. Our experiments involve the femtosecond trapping laser tunable from 740-820 nm at low power 25 mW to cause heating in the trapped volume within a homogeneous solution of sub micro-molar concentration of IR dye. The 780 nm high repetition rate laser acts as a resonant excitation source which helps to create the local heating effortlessly within the trapping volume. We have used both position autocorrelation and equipartion theorem to evaluate temperature at different wavelength having different absorption coefficient. Fixing the pulse width in the temporal domain gives constant bandwidth at spatial domain, which makes our system behave as a tunable temperature rise device with high precision. This observation leads us to calculate temperature as well as viscosity within the vicinity of the trapping zone. A mutual energy transfer occurs between the trapped bead and solvents that leads to transfer the thermal energy of solvents into the kinetic energy of the trap bead and vice-versa. Thus hot solvated molecules resulting from resonant and near resonant excitation of trapping wavelength can continuously dissipate heat to the trapped bead which will be reflected on frequency spectrum of Brownian noise exhibited by the bead. Temperature rise near the trapping zone can significantly change the viscosity of the medium. We observe temperature rise profile according to its Gaussian shaped absorption spectrum with different wavelength.

     BibTeX: @inproceedings{mondalTemperatureControlMeasurement2016,
      title = {Temperature Control and Measurement with Tunable Femtosecond Optical Tweezers},
      booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIII}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-09-16},
      volume = {9922},
      pages = {992210},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5mr2},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9922/992210/Temperature-control-and-measurement-with-tunable-femtosecond-optical-tweezers/10.1117/12.2237708.short},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XIII}}}
    }
    

17. Two-Photon Absorption Cross Sections in a Dual-Signaling Ferrocene Pyrene Conjugate. M. D. Pandey, S. K. Maurya, D. Goswami, M. A. Wani, and R. Pandey, 2 (2016) [Abstract] [BibTeX]

    Abstract: We report a ferrocene-pyrene conjugate (1) as an electroactive and photoactive signaling units. Copper mediated system selectively shows highly two-photon absorption activity 1230 GM at 780 nm, in contrast to strong one-photon fluorescence quenching.

     BibTeX: @article{pandeyTwophotonAbsorptionCross2016,
      title = {Two-Photon Absorption Cross Sections in a Dual-Signaling Ferrocene Pyrene Conjugate},
      author = {Pandey, Mrituanjay D and Maurya, Sandeep Kumar and Goswami, Debabrata and Wani, Manzoor Ahmad and Pandey, Rampal},
      date = {2016},
      pages = {2},
      doi = {10/gf8pjt}
    }
    

18. Structure and Dynamics of Optically Directed Self-Assembly of Nanoparticles. D. Roy, D. Mondal, and D. Goswami, Scientific Reports 6, 23318 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: Self-assembly of nanoparticles leading to the formation of colloidal clusters often serves as the representative analogue for understanding molecular assembly. Unravelling the in situ structure and dynamics of such clusters in liquid suspensions is highly challenging. Presently colloidal clusters are first isolated from their generating environment and then their structures are probed by light scattering methods. In order to measure the in situ structure and dynamics of colloidal clusters, we have generated them using the high-repetition-rate femtosecond laser pulse optical tweezer. Since the constituent of our dimer, trimer or tetramer clusters are 250 nm radius two-photon resonant fluorophore coated nanospheres under the optical trap, they inherently produce Two-Photon Fluorescence, which undergo intra-nanosphere Fluorescence Energy Transfer. This unique energy transfer signature, in turn, enables us to visualize structures and orientations of these colloidal clusters during the process of their formation and subsequent dynamics in a liquid suspension. We also show that due to shape-birefringence, orientation and structural control of these colloidal clusters are possible as the polarization of the trapping laser is changed from linear to circular. We thus report important progress in sampling the smallest possible aggregates of nanoparticles, dimers, trimers or tetramers, formed early in the self-assembly process.

     BibTeX: @article{royStructureDynamicsOptically2016,
      title = {Structure and Dynamics of Optically Directed Self-Assembly of Nanoparticles},
      author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-03-23},
      journaltitle = {Scientific Reports},
      volume = {6},
      pages = {23318},
      issn = {2045-2322},
      doi = {10/f8fjqk},
      url = {https://www.nature.com/articles/srep23318},
      urldate = {2019-08-01}
    }
    

19. Two-Photon Fluorescence Tracking of Colloidal Clusters. D. Roy, D. Mondal, and D. Goswami, Journal of Fluorescence 26(4), 1271–1277 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: In situ dynamics of colloidal cluster formation from nanoparticles is yet to be addressed. Using two-photon fluorescence (TPF) that has been amply used for single particle tracking, we demonstrate in situ measurement of effective three-dimensional optical trap stiffness of nanoparticles and their aggregates without using any position sensitive detector. Optical trap stiffness is an essential measure of the strength of an optical trap. TPF is a zero-background detection scheme and has excellent signal-to-noise-ratio, which can be easily extended to study the formation of colloidal cluster of nanospheres in the optical trapping regime. TPF tracking can successfully distinguish colloidal cluster from its monomer.

     BibTeX: @article{royTwoPhotonFluorescenceTracking2016,
      title = {Two-{{Photon Fluorescence Tracking}} of {{Colloidal Clusters}}},
      author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
      date = {2016-07-01},
      journaltitle = {Journal of Fluorescence},
      shortjournal = {J Fluoresc},
      volume = {26},
      number = {4},
      pages = {1271--1277},
      issn = {1573-4994},
      doi = {10/f82fs3},
      url = {https://doi.org/10.1007/s10895-016-1814-3},
      urldate = {2019-08-01}
    }
    

20. Sensitive Dual Beam Thermal Lens Detection of Convection in Methanol. S. Singhal and D. Goswami, in 13th International Conference on Fiber Optics and Photonics (OSA, 2016), p. P1A.16 [Abstract] [PDF] [BibTeX]

    Abstract: We show that dual beam mode mismatched thermal lens (TL) technique is more sensitive than the single beam one. Presence of unusual peak inside the dual beam TL signal directly indicates strong convection.

     BibTeX: @inproceedings{singhalSensitiveDualBeam2016,
      title = {Sensitive Dual Beam Thermal Lens Detection of Convection in Methanol},
      booktitle = {13th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Singhal, Sumit and Goswami, Debabrata},
      date = {2016},
      pages = {P1A.16},
      publisher = {{OSA}},
      location = {{Kanpur}},
      doi = {10/gf5mrn},
      url = {https://www.osapublishing.org/abstract.cfm?URI=Photonics-2016-P1A.16},
      urldate = {2019-08-01},
      eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
      isbn = {978-1-943580-22-4}
    }
    

21. Nonlinear Absorption in Tetrathia[22]Porphyrin(2.1.2.1)s: Visualizing Strong Reverse Saturable Absorption at Non-Resonant Excitation. K. Singh, S. Arora, K. Makhal, P. Kaur, and D. Goswami, RSC Advances 6(27), 22659–22663 (2016) [Abstract] [PDF] [BibTeX]

    Abstract: The nonlinear optical absorption properties of three meso-substituted aromatic, neutral tetrathia[22]porphyrin(2.1.2.1) compounds were investigated using an open aperture Z-scan technique at 527 nm with a pulse width of 100 ns in dichloromethane. The responses obtained were accounted for by invoking reverse saturable absorption arising due to strong excited state absorption. Both ground and excited state absorption cross-sections are reported, which follow the same trend as the respective structural parameters.

     BibTeX: @article{singhNonlinearAbsorptionTetrathia2016,
      title = {Nonlinear Absorption in Tetrathia[22]Porphyrin(2.1.2.1)s: Visualizing Strong Reverse Saturable Absorption at Non-Resonant Excitation},
      shorttitle = {Nonlinear Absorption in Tetrathia[22]Porphyrin(2.1.2.1)s},
      author = {Singh, Kamaljit and Arora, Shafali and Makhal, Krishnandu and Kaur, Paramjit and Goswami, Debabrata},
      date = {2016},
      journaltitle = {RSC Advances},
      volume = {6},
      number = {27},
      pages = {22659--22663},
      doi = {10/gf5mr9},
      url = {https://pubs.rsc.org/en/content/articlelanding/2016/ra/c5ra22861a},
      urldate = {2019-08-01}
    }
    

2015

1. Future Challenges: General Discussion. Faraday Discussions 177(0), 517–545 (2015) [PDF] [BibTeX]

    BibTeX: @article{d.jemmisFutureChallengesGeneral2015,
     title = {Future Challenges: General Discussion},
     shorttitle = {Future Challenges},
     author = {},
     date = {2015},
     journaltitle = {Faraday Discussions},
     volume = {177},
     number = {0},
     pages = {517--545},
     doi = {10/gf5ms3},
     url = {https://my.pcloud.com/publink/show?code=XZtIxr7Zt8MyC5erIwYzX49baog4w0S8DjUV},
     urldate = {2019-08-01}
   }
   

2. Sensing near the Liquid:Liquid Interface Remotely via Ultrafast Pump Probe Study. D. K. Das, K. Makhal, and D. Goswami, in 2015 Workshop on Recent Advances in Photonics (WRAP) (2015), pp. 1–4 [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast pump-probe technique has been invoked to understand the liquid:liquid interface by using a cyanine dye dissolved in dimethyl sulfoxide (DMSO), interfaced with neat diethyl-ether (Et2O). We show that the dynamics of the dye gets slow down on moving from the bulk dye solution in DMSO towards the interface with neat-diethyl ether. Hence we get an alternate picture of interface by looking at the time constants. Four time constants were used for fitting the experimental data which are assigned to be coherent artifact, vibrational cooling, intermediate state time and finally ground state recovery time. The drastic change in signal was observed at a distance of 0.1 mm from the interface. The decreasing time constants from bulk to near interfaced solution strongly suggests involvement of heterogeneity in the system because of the penetration of diethyl ether through the interface into the DMSO layer where the dye is dissolved, which strongly affects the dynamics at near the interface of the DMSO with neat-diethyl ether layer (at 0.1 mm distance from the interface).

    BibTeX: @inproceedings{dasSensingLiquidLiquid2015,
     title = {Sensing near the Liquid:Liquid Interface Remotely via Ultrafast Pump Probe Study},
     shorttitle = {Sensing near the Liquid},
     booktitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Das, D. K. and Makhal, K. and Goswami, D.},
     date = {2015-12},
     pages = {1--4},
     doi = {10/gf5msb},
     url = {https://my.pcloud.com/publink/show?code=XZfAxr7ZEoKkOTQY1W73Rb0uatplJzuKxRvV},
     eventtitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

3. Entropy-Driven Formation of Large Icosahedral Colloidal Clusters by Spherical Confinement. Nature Materials 14(1), 56–60 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids1,2,3,4,5,6,7,8,9,10,11,12. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential1,3,6,7,8,9,10,11,12. Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure13,14. Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.

    BibTeX: @article{denijsEntropydrivenFormationLarge2015,
     title = {Entropy-Driven Formation of Large Icosahedral Colloidal Clusters by Spherical Confinement},
     author = {},
     date = {2015-01},
     journaltitle = {Nature Materials},
     volume = {14},
     number = {1},
     pages = {56--60},
     issn = {1476-4660},
     doi = {10/gf85zc},
     url = {https://www.nature.com/articles/nmat4072},
     urldate = {2019-10-01}
   }
   

4. Dynamics of Chemical Bond: General Discussion. K. Dhoke, M. Zanni, U. Harbola, R. K. Venkatraman, E. Arunan, K.-C. Lin, A. Nenov, J. Skelton, R. J. D. Miller, J. D. Hirst, V. Aquilanti, J. R. Helliwell, S. Keshavamurthy, S. Ramesh, M. Ashfold, A. Pallipurath, P. Roy Chowdhury, S. Mukhopadhyay, J. E D, H. Medhi, D. Goswami, P. Halder, W. Junge, M. Hariharan, S. K. Singh, S. Umapathy, A. Lakshmannam, M. Meedom Nielsen, S. Aravamudhan, V. Deckert, K. Ghiggino, K. Tominaga, and A. Edwards, Faraday Discussions 177, 121–154 (2015) [PDF] [BibTeX]

    BibTeX: @article{dhokeDynamicsChemicalBond2015,
     title = {Dynamics of Chemical Bond: General Discussion},
     shorttitle = {Dynamics of Chemical Bond},
     author = {Dhoke, Kunal and Zanni, Martin and Harbola, Upendra and Venkatraman, Ravi Kumar and Arunan, Elangannan and Lin, King-Chuen and Nenov, Artur and Skelton, Jonathan and Miller, R J Dwayne and Hirst, Jonathan D. and Aquilanti, Vincenzo and Helliwell, John R. and Keshavamurthy, Srihari and Ramesh, Sai and Ashfold, Mike and Pallipurath, Anuradha and Roy Chowdhury, Priyadarshi and Mukhopadhyay, Sanghamitra and E D, Jemmis and Medhi, Himani and Goswami, Debabrata and Halder, Prasenjit and Junge, Wolfgang and Hariharan, Mahesh and Singh, Santosh Kumar and Umapathy, Siva and Lakshmannam, Adithya and Meedom Nielsen, Martin and Aravamudhan, Sankarampadi and Deckert, Volker and Ghiggino, Kenneth and Tominaga, Keisuke and Edwards, Alison},
     date = {2015},
     journaltitle = {Faraday Discussions},
     shortjournal = {Faraday Discuss.},
     volume = {177},
     pages = {121--154},
     issn = {1359-6640, 1364-5498},
     doi = {10/gf5mss},
     url = {https://my.pcloud.com/publink/show?code=XZhaxr7ZFTPN6Cuqf08xjq5XSTjI4zaNU8Sy},
     urldate = {2019-08-01}
   }
   

5. Controlled Heteroaggregation of Two Types of Nanoparticles in an Aqueous Suspension. P. Dušak, A. Mertelj, S. Kralj, and D. Makovec, Journal of Colloid and Interface Science 438, 235–243 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Composite particles combining nanoparticles of different functional materials, as well as nanoclusters of nanoparticles of controlled size, can be synthesized by the assembly of nanoparticles in an aqueous suspension. Different interactions between the nanoparticles in the suspension can be applied for their heteroaggregation and controlled by engineering the surface properties of the nanoparticles. The heteroaggregation of nanoparticles in a suspension was studied on a model system composed of superparamagnetic carboxyl-functionalized silica-coated maghemite nanoparticles (cMNPs) (24nm in size) and larger, amino-functionalized, silica nanoparticles (aSNPs) (92nm). The heteroaggregates formed with electrostatic attractions between the nanoparticles displaying an opposite electrical surface charge, or with chemical interactions originating from covalent bonding between the molecules at their surfaces. The suspensions were characterized with measurements of the zeta-potential and dynamic light scattering (DLS). The heteroaggregates were analyzed by transmission (TEM) and scanning (SEM) electron microscopy. The kinetics of the heteroaggregation was followed by continuous monitoring of the changes in the average hydrodynamic size by DLS. The results show that covalent bonding is much more effective than attractive electrostatic interactions in terms of a much greater and more homogeneous coverage of the larger central aSNP by the smaller cMNPs in the outer layer.

    BibTeX: @article{dusakControlledHeteroaggregationTwo2015,
     title = {Controlled Heteroaggregation of Two Types of Nanoparticles in an Aqueous Suspension},
     author = {Dušak, Peter and Mertelj, Alenka and Kralj, Slavko and Makovec, Darko},
     date = {2015-01-15},
     journaltitle = {Journal of Colloid and Interface Science},
     shortjournal = {Journal of Colloid and Interface Science},
     volume = {438},
     pages = {235--243},
     issn = {0021-9797},
     doi = {10/f6tfsv},
     url = {http://www.sciencedirect.com/science/article/pii/S0021979714007504},
     urldate = {2019-10-01}
   }
   

6. Advanced Optical Developments for Inter-Satellite Communication. D. Goswami, 5 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: One of the most common and effective usage of free space communication (FSO) is in the information transfer between satellites, which at present is mostly based on wireless Radio frequency (RF). FSO is a telecommunications technology that transmits and receives data in the form of optical signal through an unguided channel from one point to another point. The theory of FSO is essentially the same as that for fiber optic transmission. The difference is that the energy beam is collimated and sent through clear air or space from the source to destination, rather than guided through an optical fiber. While optical fiber has emerged as the major communication channel for terrestrial communication due to the difficulty of finding effective line of sight in terrestrial space needed for FSO, it remains as one of the most effective means for space applications, especially for inter-satellite communication. Our research is focusing on such advanced optical technology as the effective transmitter for free-space communication.

    BibTeX: @article{goswamiAdvancedOpticalDevelopments2015,
     title = {Advanced {{Optical Developments}} for Inter-{{Satellite Communication}}},
     author = {Goswami, Debabrata},
     date = {2015},
     pages = {5},
     url = {http://pc.cd/LaaitalK}
   }
   

7. Demonstrating a Nano Viscometer Using Femtosecond Laser Induced Photo-Thermal Effect. D. Goswami, in 2015 Workshop on Recent Advances in Photonics (WRAP) (2015), pp. 1–4 [Abstract] [PDF] [BibTeX]

   Abstract: We present a new method to utilize photo-thermal effect at nano-volume dimension, to measure viscosity, which could be useful to eventually correlate to in-vivo conditions. We present our measurements using high repetition rate low average power femtosecond laser induced conditions under which the photo-thermal effect is highly influence by the convective mode of heat transfer. This is especially important in absorbing liquids. This is unlike the typical photo-thermal conditions not involving such ultrashort pulses. Typical thermal processes involve only conductive mode of heat transfer and are phenomenological in nature. Inclusion of convective mode results in some additional molecular characteristics to the thermal process. We measure the traditional thermal lens studies with femtosecond pulse train through geometric beam divergence of a collimated laser beam co-propagating with the focused heating laser beam. The refractive index gradient in the sample due to the focused heating laser creates a thermal lens, which is measured. On the other hand, the same heat gradient from the focusing heating laser beam generates a change in local viscosity in the medium, which changes the trapped stiffness of an optically trapped microsphere in its vicinity. We use co-propagating femtosecond train of laser pulses of wavelength 1560 nm and 780 nm for these experiments. From the bulk thermal studies, we show that use of water as sample provides us the advantage to use conductive mode of heat transfer even with femtosecond pulse train excitation.

    BibTeX: @inproceedings{goswamiDemonstratingNanoViscometer2015,
     title = {Demonstrating a Nano Viscometer Using Femtosecond Laser Induced Photo-Thermal Effect},
     booktitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
     author = {Goswami, D.},
     date = {2015-12},
     pages = {1--4},
     doi = {10/gf5msc},
     url = {https://my.pcloud.com/publink/show?code=XZUGxr7ZadBLrqnQAXVhW2jQ8UVesyuCjpny},
     eventtitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
   }
   

8. Lasers and Their Applications. D. Goswami, 18 (2015) [Abstract] [PDF] [BibTeX]

   Abstract: Ever since the advent of the first LASER (acronym for Light Amplification by Stimulation Emission of Radiation) in 1960, there has been a steady increase in the application of lasers. Applications have kept on becoming more and more diverse as the capability of the lasers have increased. In this chapter we will enumerate and classify many of the applications of lasers and then go on to discuss in more detail some of the more modern applications.

    BibTeX: @article{goswamiLasersTheirApplications2015,
     title = {Lasers and Their {{Applications}}},
     author = {Goswami, Debabrata},
     date = {2015},
     pages = {18},
     url = {https://my.pcloud.com/publink/show?code=XZeoxr7ZHDcE2BJfa3pk2RL7TQEYeQyTevSk}
   }
   

9. Measurement Constraints in Laser Based Thermal Lens Experiments. D. Goswami and P. Kumar, in International Conference on Optics and Photonics 2015 (International Society for Optics and Photonics, 2015), 9654, p. 965406 [Abstract] [PDF] [BibTeX]

   Abstract: Importance of various measurement schemes in studying thermal lens (TL) signal for laser based TL experiments is explored. We show that two different measurement schemes can result in two contrasting outcomes. In one experiment, two measurement schemes show diverging results for TL signal measurements, which gives a convoluted result and in the other experiment, the two measurement schemes give a converging result.

    BibTeX: @inproceedings{goswamiMeasurementConstraintsLaser2015,
     title = {Measurement Constraints in Laser Based Thermal Lens Experiments},
     booktitle = {International {{Conference}} on {{Optics}} and {{Photonics}} 2015},
     author = {Goswami, Debabrata and Kumar, Pardeep},
     date = {2015-06-15},
     volume = {9654},
     pages = {965406},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/gf5msn},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9654/965406/Measurement-constraints-in-laser-based-thermal-lens-experiments/10.1117/12.2192167.short},
     urldate = {2019-08-01},
     eventtitle = {International {{Conference}} on {{Optics}} and {{Photonics}} 2015}
   }
   

10. Resolution Enhancement through Microscopic Spatiotemporal Control. D. Goswami, D. Das, and S. N. Bandyopadhyay, Faraday Discussions 177(0), 203–212 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: Operating at biologically benign conditions, multi-photon fluorescence imaging microscopy has benefitted immensely from recent developments in microscopic resolution enhancement. Fluorescence microscopy continues to be the best choice for experiments on live specimens, however, multi-photon fluorescence imaging often suffers from overlapping fluorescence of typical dyes used in microscopy, limiting its scope. This limitation has been the focus of our research where we show that by making simple modifications to the laser pulse structure, it is possible to resolve these overlapping fluorescence complications. Specifically, by using pairs of femtosecond pulses with variable delay in place of single pulse excitation, we show controlled fluorescence excitation or suppression of one of the fluorophores over the other through wave-packet interferometry. Such an effect prevails even after the fluorophore coherence timescale, which effectively results in a higher spatial resolution. Here we extend the effect of our pulse-pair technique to microscopic axial resolution experiments and show that such pairs of pulses can also ‘enhance’ axial resolution.

     BibTeX: @article{goswamiResolutionEnhancementMicroscopic2015,
      title = {Resolution Enhancement through Microscopic Spatiotemporal Control},
      author = {Goswami, Debabrata and Das, Dhiman and Bandyopadhyay, Soumendra Nath},
      date = {2015-04-14},
      journaltitle = {Faraday Discussions},
      shortjournal = {Faraday Discuss.},
      volume = {177},
      number = {0},
      pages = {203--212},
      issn = {1364-5498},
      doi = {10/gf5msv},
      url = {https://my.pcloud.com/publink/show?code=XZzvxr7Z0vbvki6gLSQhR76QzRco87Moa8Fy},
      urldate = {2019-08-01}
    }
    

11. Effect of Zinc Substitution on Molecular Dynamics of Protoporphyrin-IX. A. Kumar and D. Goswami, Indian Journal of Physics 89(11), 1183–1192 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: We report the effects of zinc metal substitution on the molecular dynamics of protoporphyrin-IX in dichloromethane solvent by spectrally resolving the femtosecond photon echo spectrum. We have found that the coherence and population dynamics change due to the presence of Zn metal in the protoporphyrin-IX system. Zinc metal reduces the conformational disorder in the molecular structure of protoporphyrin-IX and in turn increases the planarity of the molecule resulting in better delocalization of π-electrons in the system. This effect decreases the inhomogeneous broadening of the photon echo spectra of Zn-substituted protoporphyrin-IX.

     BibTeX: @article{kumarEffectZincSubstitution2015,
      title = {Effect of Zinc Substitution on Molecular Dynamics of Protoporphyrin-{{IX}}},
      author = {Kumar, A. and Goswami, D.},
      date = {2015-11-01},
      journaltitle = {Indian Journal of Physics},
      shortjournal = {Indian J Phys},
      volume = {89},
      number = {11},
      pages = {1183--1192},
      issn = {0974-9845},
      doi = {10/f73kth},
      url = {https://doi.org/10.1007/s12648-015-0689-5},
      urldate = {2019-08-01}
    }
    

12. Study of Two Xanthene Dyes Using Spectrally Resolved Three-Pulse Photon Echo Spectroscopy. A. Kumar, S. K. K. Kumar, S. Singhal, and D. Goswami, Current Science 108(10), 1801–1803 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: Comparitive study of the molecular dynamics of two xanthene dye derivatives (Rhodamine-6G and Fluorescein-548) is reported using spectrally resolved three-pulse photon echo spectroscopy. An appreciable change in the coherence and population dynamics was observed between the two xanthene derivatives due to the presence of different functional groups. Solution of Rhodamine-6G in methanol behaves in a more coherent fashion compared to that of Fluorescein-548 dye.

     BibTeX: @article{kumarStudyTwoXanthene2015,
      title = {Study of Two Xanthene Dyes Using Spectrally Resolved Three-Pulse Photon Echo Spectroscopy},
      author = {Kumar, Ajitesh and Kumar, S. K. Karthick and Singhal, Sumit and Goswami, Debabrata},
      date = {2015},
      journaltitle = {Current Science},
      volume = {108},
      number = {10},
      eprint = {24905603},
      eprinttype = {jstor},
      pages = {1801--1803},
      issn = {0011-3891},
      url = {https://www.jstor.org/stable/24905603},
      urldate = {2019-08-01}
    }
    

13. Calibration of Femtosecond Optical Tweezers as a Sensitive Thermometer. D. Mondal and D. Goswami, in Optical Trapping and Optical Micromanipulation XII (International Society for Optics and Photonics, 2015), 9548, p. 95481N [Abstract] [PDF] [BibTeX]

    Abstract: We present cumulative perturbation effects of femtosecond laser pulses on an optical tweezer. Our experiments involve a dual wavelength high repetition rate femtosecond laser, one at the non-heating wavelength of 780 nm while the other at 1560 nm to cause heating in the trapped volume under low power (100-800 μW) conditions. The 1560 nm high repetition rate laser acts as a resonant excitation source for the vibrational combination band of the hydroxyl group (OH) of water, which helps create the local heating effortlessly within the trapping volume. With such an experimental system, we are the first to observe direct effect of temperature on the corner frequency deduced from power spectrum. We can, thus, control and measure temperature precisely at the optical trap. This observation has lead us to calculate viscosity as well as temperature in the vicinity of the trapping zone. These experimental results also support the well-known fact that the nature of Brownian motion is the response of the optically trapped bead from the temperature change of surroundings. Temperature rise near the trapping zone can significantly change the viscosity of the medium. However, we notice that though the temperature and viscosity are changing as per our corner frequency calculations, the trap stiffness remains the same throughout our experiments within the temperature range of about 20 K.

     BibTeX: @inproceedings{mondalCalibrationFemtosecondOptical2015,
      title = {Calibration of Femtosecond Optical Tweezers as a Sensitive Thermometer},
      booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation XII}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2015-08-25},
      volume = {9548},
      pages = {95481N},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/gf5msk},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9548/95481N/Calibration-of-femtosecond-optical-tweezers-as-a-sensitive-thermometer/10.1117/12.2187097.short},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation XII}}}
    }
    

14. Controlling the Effect on Solvent by Resonant Excitation in Femtosecond Optical Tweezer. D. Mondal and D. Goswami, in Optics in the Life Sciences (OSA, 2015), p. OtT4E.3 [Abstract] [PDF] [BibTeX]

    Abstract: Observation of direct effect of temperature rise in water around optical trap center is presented. Irradiation of IR laser with low power during pulsed 780 nm trapping significantly changes solvent viscosity keeping trap stiffness unaffected.

     BibTeX: @inproceedings{mondalControllingEffectSolvent2015,
      title = {Controlling the Effect on Solvent by Resonant Excitation in Femtosecond Optical Tweezer},
      booktitle = {Optics in the {{Life Sciences}}},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2015},
      pages = {OtT4E.3},
      publisher = {{OSA}},
      location = {{Vancouver}},
      doi = {10/gf5msw},
      url = {https://www.osapublishing.org/abstract.cfm?URI=OTA-2015-OtT4E.3},
      urldate = {2019-08-01},
      eventtitle = {Optical {{Trapping Applications}}},
      isbn = {978-1-55752-954-1}
    }
    

15. Controlling Local Temperature in Water Using Femtosecond Optical Tweezer. D. Mondal and D. Goswami, Biomedical Optics Express 6(9), 3190–3196 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: A novel method of directly observing the effect of temperature rise in water at the vicinity of optical trap center is presented. Our approach relies on changed values of corner frequency of the optical trap that, in turn, is realized from its power spectra. Our two color experiment is a unique combination of a non-heating femtosecond trapping laser at 780 nm, coupled to a femtosecond infrared heating laser at 1560 nm, which precisely controls temperature at focal volume of the trap center using low powers (100-800 µW) at high repetition rate. The geometric ray optics model quantitatively supports our experimental data.

     BibTeX: @article{mondalControllingLocalTemperature2015,
      title = {Controlling Local Temperature in Water Using Femtosecond Optical Tweezer},
      author = {Mondal, Dipankar and Goswami, Debabrata},
      date = {2015-09-01},
      journaltitle = {Biomedical Optics Express},
      shortjournal = {Biomed. Opt. Express, BOE},
      volume = {6},
      number = {9},
      pages = {3190--3196},
      issn = {2156-7085},
      doi = {10/gf5msh},
      url = {https://www.osapublishing.org/boe/abstract.cfm?uri=boe-6-9-3190},
      urldate = {2019-08-01}
    }
    

16. Spatiotemporal Control of Energy Transfer in Optically Trapped Systems. D. Mondal, D. Roy, and D. Goswami, in 2015 International Young Scientists Forum on Applied Physics (YSF) (2015), pp. 1–4 [Abstract] [BibTeX]

    Abstract: We demonstrate control over two photon fluorescence (TPF) resonance energy transfer under femtosecond optically tweezed condition. We also extract information about the structure and dynamics of the trapped particles and their clusters as observed from the TPF decay times of the trapped multiple microspheres (0.50 μm size) by varying the polarization of the trapping laser. This micron to nano regime of the energy transfer process has provided us the necessary control over the molecular level energy transfer rate due to the different overlap integral of excitation and emission spectra of the dye that is coated on the surface of 1.0 μm polystyrene particles. Our background free detection method thus provides additional structural information about multiple trapping events.

     BibTeX: @inproceedings{mondalSpatiotemporalControlEnergy2015,
      title = {Spatiotemporal Control of Energy Transfer in Optically Trapped Systems},
      booktitle = {2015 {{International Young Scientists Forum}} on {{Applied Physics}} ({{YSF}})},
      author = {Mondal, D. and Roy, D. and Goswami, D.},
      date = {2015-09},
      pages = {1--4},
      doi = {10/gf5msz},
      eventtitle = {2015 {{International Young Scientists Forum}} on {{Applied Physics}} ({{YSF}})}
    }
    

17. Elucidating Microscopic Structure and Dynamics in Optically Tweezed Environments. D. Roy, D. Mondal, and D. Goswami, Chemical Physics Letters 621, 203–208 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: To probe the structure and dynamics of molecules under optical trapping conditions, we exploit the effect of femtosecond Fluorescence Resonance Energy Transfer (FRET) between dye molecules coated on the surface of polystyrene microspheres of various sizes suspended in water. The use of femtosecond laser pulses enables sensitive detection through two-photon fluorescence (TPF). Unlike conventional backscatter signal, the TPF signal shows a slow counterintuitive decay for the trapped microspheres when they are not fully within the laser illuminated volume. This decay is a characteristic sign of the occurrence of the FRET process. For microspheres with sizes less than the trapping focal volume, trapping of multiple particles can occur leading to the formation of optically bound clusters. Using different laser polarizations, we also extract information about the structure and dynamics of such optically bound clusters as a consequence of FRET.

     BibTeX: @article{royElucidatingMicroscopicStructure2015,
      title = {Elucidating Microscopic Structure and Dynamics in Optically Tweezed Environments},
      author = {Roy, Debjit and Mondal, Dipankar and Goswami, Debabrata},
      date = {2015-02-04},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {621},
      pages = {203--208},
      issn = {0009-2614},
      doi = {10/f6zd8x},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261414009658},
      urldate = {2019-08-01}
    }
    

18. Exploring the Physics of Efficient Optical Trapping of Dielectric Nanoparticles with Ultrafast Pulsed Excitation. D. Roy, D. Goswami, and A. K. De, Applied Optics 54(23), 7002 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: Stable optical trapping of dielectric nanoparticles with low power high-repetition-rate ultrafast pulsed excitation has received considerable attention in recent years. However, the exact role of such excitation has been quite illusive so far since, for dielectric micron-sized particles, the trapping efficiency turns out to be similar to that of continuous-wave excitation and independent of pulse chirping. In order to provide a coherent explanation of this apparently puzzling phenomenon, we justify the superior role of high-repetition-rate pulsed excitation in dielectric nanoparticle trapping which is otherwise not possible with continuous-wave excitation at a similar average power level. We quantitatively estimate the optimal combination of pulse peak power and pulse repetition rate leading to a stable trap and discuss the role of inertial response on the dependence of trapping efficiency on pulse width. In addition, we report gradual trapping of individual quantum dots detected by a stepwise rise in a two-photon fluorescence signal from the trapped quantum dots which conclusively proves individual particle trapping.

     BibTeX: @article{royExploringPhysicsEfficient2015,
      title = {Exploring the Physics of Efficient Optical Trapping of Dielectric Nanoparticles with Ultrafast Pulsed Excitation},
      author = {Roy, Debjit and Goswami, Debabrata and De, Arijit K.},
      date = {2015-08-10},
      journaltitle = {Applied Optics},
      shortjournal = {Appl. Opt.},
      volume = {54},
      number = {23},
      pages = {7002},
      issn = {0003-6935, 1539-4522},
      doi = {10/gf5msm},
      url = {https://www.osapublishing.org/abstract.cfm?URI=ao-54-23-7002},
      urldate = {2019-08-01}
    }
    

19. Exploring the Critical Role of Detection Aperture in Thermal Lens Measurements. S. Singhal, I. Bhattacharyya, and D. Goswami, in 2015 Workshop on Recent Advances in Photonics (WRAP) (2015), pp. 1–4 [Abstract] [BibTeX]

    Abstract: The critical role of the detection aperture size on the measurement of thermal lens signals has been explored by using mode-mismatched pump-probe thermal lens spectroscopy in pure methanol. Femtosecond laser pulses at 1560 nm are used to create thermal lens signal, which is simultaneously probed by a collinear 780 nm pulse train through a partially open aperture of different sizes placed after the sample. The trend in the time resolved thermal lens signals reveals that aperture size allowing less than half of the incident probe light is critical in providing accuracy of the thermal lens spectroscopy.

     BibTeX: @inproceedings{singhalExploringCriticalRole2015,
      title = {Exploring the Critical Role of Detection Aperture in Thermal Lens Measurements},
      booktitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})},
      author = {Singhal, S. and Bhattacharyya, I. and Goswami, D.},
      date = {2015-12},
      pages = {1--4},
      doi = {10/gf5msd},
      eventtitle = {2015 {{Workshop}} on {{Recent Advances}} in {{Photonics}} ({{WRAP}})}
    }
    

20. Importance of Hydrogen Bonding in Thermal Lens Study of Highly Absorbing Liquids. S. Singhal, P. P. Roy, and D. Goswami, in Frontiers in Optics 2015 (2015), Paper FTu5E.5 (Optical Society of America, 2015), p. FTu5E.5 [Abstract] [PDF] [BibTeX]

    Abstract: Effect of thermal load on highly absorbing hydrogen bonded liquids are explored. We find heat transfer is better facilitated in lesser hydrogen bonded liquids by convection through molecular motion in addition to conduction.

     BibTeX: @inproceedings{singhalImportanceHydrogenBonding2015,
      title = {Importance of {{Hydrogen Bonding}} in {{Thermal Lens Study}} of {{Highly Absorbing Liquids}}},
      booktitle = {Frontiers in {{Optics}} 2015 (2015), Paper {{FTu5E}}.5},
      author = {Singhal, Sumit and Roy, Partha Pratim and Goswami, Debabrata},
      date = {2015-10-18},
      pages = {FTu5E.5},
      publisher = {{Optical Society of America}},
      doi = {10/gf5msf},
      url = {https://www.osapublishing.org/abstract.cfm?uri=FiO-2015-FTu5E.5},
      urldate = {2019-08-01},
      eventtitle = {Frontiers in {{Optics}}}
    }
    

21. Local and Global Dynamics: General Discussion. M. Zanni, E. D. Jemmis, S. Aravamudhan, E. Arunan, N. Hunt, S. Mukhopadhyay, H. J. Shepherd, S. Keshavamurthy, A. G. Dijkstra, M. Ashfold, H. P. Goswami, A. Nenov, H. Medhi, K. Ghiggino, K. Moirangthem, R. J. Dwayne Miller, D. Goswami, S. Umapathy, J. R. Helliwell, J. D. Hirst, S. Meech, S. Mukamel, B. Bagchi, and M. B.-L. Cointe, Faraday Discussions 177(0), 381–403 (2015) [PDF] [BibTeX]

     BibTeX: @article{zanniLocalGlobalDynamics2015,
      title = {Local and {{Global Dynamics}}: General Discussion},
      shorttitle = {Local and {{Global Dynamics}}},
      author = {Zanni, Martin and D.~Jemmis, E. and Aravamudhan, Sankarampadi and Arunan, Elangannan and Hunt, Neil and Mukhopadhyay, Sanghamitra and J.~Shepherd, Helena and Keshavamurthy, Srihari and G.~Dijkstra, Arend and Ashfold, Mike and Goswami, Himangshu Prabal and Nenov, Artur and Medhi, Himani and Ghiggino, Kenneth and Moirangthem, Kiran and Dwayne~Miller, R. J. and Goswami, Debabrata and Umapathy, Siva and R.~Helliwell, John and D.~Hirst, Jonathan and Meech, Stephen and Mukamel, Shaul and Bagchi, Biman and Cointe, Marylise Buron-Le},
      date = {2015},
      journaltitle = {Faraday Discussions},
      volume = {177},
      number = {0},
      pages = {381--403},
      doi = {10/gf5ms2},
      url = {https://pubs.rsc.org/en/content/articlelanding/2015/fd/c5fd90018b},
      urldate = {2019-08-01}
    }
    

22. Time and Space Resolved Methods: General Discussion. M. Zanni, J. E. D, S. Aravamudhan, A. Pallipurath, E. Arunan, C. Schnedermann, A. K. Mishra, M. Warren, J. D. Hirst, F. John, R. Pal, J. R. Helliwell, K. Moirangthem, S. Chakraborty, A. G. Dijkstra, P. R. Chowdhury, K. Ghiggino, R. J. D. Miller, S. Meech, H. Medhi, M. Hariharan, F. Ariese, A. Edwards, A. R. Mallia, S. Umapathy, M. M. Nielsen, N. Hunt, Z.-Y. Tian, J. Skelton, G. Sankar, and D. Goswami, Faraday Discussions 177(0), 263–292 (2015) [Abstract] [PDF] [BibTeX]

    Abstract: No abstract available

     BibTeX: @article{zanniTimeSpaceResolved2015,
      title = {Time and {{Space}} Resolved {{Methods}}: General Discussion},
      shorttitle = {Time and {{Space}} Resolved {{Methods}}},
      author = {Zanni, Martin and D, Jemmis E. and Aravamudhan, Sankarampadi and Pallipurath, Anuradha and Arunan, Elangannan and Schnedermann, Christoph and Mishra, Ashok Kumar and Warren, Mark and Hirst, Jonathan D. and John, Franklin and Pal, R. and Helliwell, John R. and Moirangthem, Kiran and Chakraborty, Shamik and Dijkstra, Arend G. and Chowdhury, Priyadarshi Roy and Ghiggino, Kenneth and Miller, R. J. Dwayne and Meech, Stephen and Medhi, Himani and Hariharan, Mahesh and Ariese, Freek and Edwards, Alison and Mallia, Ajith R. and Umapathy, Siva and Nielsen, Martin Meedom and Hunt, Neil and Tian, Zhen-Yu and Skelton, Jonathan and Sankar, Gopinathan and Goswami, Debabrata},
      date = {2015-04-14},
      journaltitle = {Faraday Discussions},
      shortjournal = {Faraday Discuss.},
      volume = {177},
      number = {0},
      pages = {263--292},
      issn = {1364-5498},
      doi = {10/gf5mst},
      url = {https://pubs.rsc.org/en/content/articlelanding/2015/fd/c5fd90017d},
      urldate = {2019-08-01}
    }
    

2014

1. Effect of Isotope Substitution in Binary Liquids with Thermal-Lens Spectroscopy. I. Bhattacharyya, P. Kumar, and D. Goswami, Chemical Physics Letters 598, 35–38 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: Effect of isotope substitution from the modulation of Thermal-Lens (TL) signals in binary liquid mixtures is explored using femtosecond pump–probe mode-mismatched Z-scan TL spectroscopy. Binary solutions of water and heavy water with pure methanol at various concentrations are used for the study, where pure methanol acts as the TL marker across the different samples. The TL signal is found to be effectively modulated by isotope substitution under the experimental conditions, indicating that TL signal depends on hydrogen bonding.

    BibTeX: @article{bhattacharyyaEffectIsotopeSubstitution2014,
     title = {Effect of Isotope Substitution in Binary Liquids with {{Thermal-Lens}} Spectroscopy},
     author = {Bhattacharyya, Indrajit and Kumar, Pardeep and Goswami, Debabrata},
     date = {2014-04-08},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {598},
     pages = {35--38},
     issn = {0009-2614},
     doi = {10/f5xrr2},
     url = {http://pc.cd/PORctalK},
     urldate = {2019-08-02}
   }
   

2. Computing with New Resources: Essays Dedicated to Jozef Gruska on the Occasion of His 80th Birthday. C. S. Calude, R. Freivalds, and I. Kazuo, (Springer, 2014) [Abstract] [BibTeX]

   Abstract: Professor Jozef Gruska is a well known computer scientist for his many and broad results. He was the father of theoretical computer science research in Czechoslovakia and among the first Slovak programmers in the early 1960s. Jozef Gruska introduced the descriptional complexity of grammars, automata, and languages, and is one of the pioneers of parallel (systolic) automata. His other main research interests include parallel systems and automata, as well as quantum information processing, transmission, and cryptography. He is co-founder of four regular series of conferences in informatics and two in quantum information processing and the Founding Chair (1989-96) of the IFIP Specialist Group on Foundations of Computer Science.

    BibTeX: @book{caludeComputingNewResources2014,
     title = {Computing with {{New Resources}}: {{Essays Dedicated}} to {{Jozef Gruska}} on the {{Occasion}} of {{His}} 80th {{Birthday}}},
     shorttitle = {Computing with {{New Resources}}},
     author = {Calude, Cristian S. and Freivalds, Rūsiņš and Kazuo, Iwama},
     date = {2014-12-09},
     eprint = {QLLLBQAAQBAJ},
     eprinttype = {googlebooks},
     publisher = {{Springer}},
     isbn = {978-3-319-13350-8},
     pagetotal = {486}
   }
   

3. Direct Observation of Coherent Oscillations in Solution Due to Microheterogeneous Environment. D. K. Das, K. Makhal, S. N. Bandyopadhyay, and D. Goswami, Scientific Reports 4, 6097 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: We report, for the first time, direct observation of coherent oscillations in the ground-state of IR775 dye due to microheterogeneous environment. Using ultrafast near-infrared degenerate pump-probe technique centered at 800 nm, we present the dynamics of IR775 in a binary mixture of methanol and chloroform at ultra-short time resolution of 30 fs. The dynamics of the dye in binary mixtures, in a time-scale of a few fs to ~740 ps, strongly varies as a function of solvent composition (volume fraction). Multi-oscillation behavior of the coherent vibration was observed, which increased with decreasing percentage of methanol in the dye mixture. Maximum number of damped oscillations were observed in 20% methanol. The observed vibrational wavepacket motion in the ground-state is periodic in nature. We needed two cosine functions to fit the coherent oscillation data as two different solvents were used. Dynamics of the dye molecule in binary mixtures can be explained by wavepacket motion in the ground potential energy surface. More is the confinement of the dye molecule in binary mixtures, more is the number of damped oscillations. The vibrational cooling time, τ2, increases with increase in the confinement of the system. The observed wavepacket oscillations in ground-state dynamics continued until 1.6 ps.

    BibTeX: @article{dasDirectObservationCoherent2014,
     title = {Direct {{Observation}} of {{Coherent Oscillations}} in {{Solution}} Due to {{Microheterogeneous Environment}}},
     author = {Das, Dipak Kumar and Makhal, Krishnandu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata},
     date = {2014-08-18},
     journaltitle = {Scientific Reports},
     volume = {4},
     pages = {6097},
     issn = {2045-2322},
     doi = {10/gf5mth},
     url = {https://www.nature.com/articles/srep06097},
     urldate = {2019-08-01}
   }
   

4. Controlled Particle Collision Leads to Direct Observation of Docking and Fusion of Lipid Droplets in an Optical Trap. C. Ghimire, D. Koirala, M. B. Mathis, E. E. Kooijman, and H. Mao, Langmuir 30(5), 1370–1375 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: As an intracellular organelle, phospholipid-coated lipid droplets have shown increasing importance due to their expanding biological functions other than the lipid storage. The growing biological significance necessitates a close scrutiny on lipid droplets, which have been proposed to mature in a cell through processes such as fusion. Unlike phospholipid vesicles that are well-known to fuse through docking and hemifusion steps, little is known on the fusion of lipid droplets. Herein, we used laser tweezers to capture two micrometer-sized 1,2,3-trioleoylglycerol (triolein) droplets coated with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) that closely resemble intracellular lipid droplets. We started the fusion processes by a well-controlled collision between the two lipid droplets in phosphate buffer at pH 7.4. By monitoring the change in the pathway of a trapping laser that captures the collided lipid droplets, docking and physical fusion events were clearly distinguished for the first time and their lifetimes were determined with a resolution of 10 μs after postsynchronization analysis. Our method revealed that the rate-limiting docking process is affected by anions according to a Hofmeister series, which sheds light on the important role of interfacial water shedding during the process. During the physical fusion, the kinetics between bare triolein droplets is faster than lipid droplets, suggesting that breaking of phospholipid coating is involved in the process. This scenario was further supported by direct observation of a short-lived hemifusion state with ∼46 ms lifetime in POPC-coated lipid droplets, but not in bare triolein droplets.

    BibTeX: @article{ghimireControlledParticleCollision2014,
     title = {Controlled {{Particle Collision Leads}} to {{Direct Observation}} of {{Docking}} and {{Fusion}} of {{Lipid Droplets}} in an {{Optical Trap}}},
     author = {Ghimire, Chiran and Koirala, Deepak and Mathis, Malcom B. and Kooijman, Edgar E. and Mao, Hanbin},
     date = {2014-02-11},
     journaltitle = {Langmuir},
     shortjournal = {Langmuir},
     volume = {30},
     number = {5},
     pages = {1370--1375},
     issn = {0743-7463},
     doi = {10/f5swjm},
     url = {https://doi.org/10.1021/la404497v},
     urldate = {2019-10-01}
   }
   

5. Highly Nonlinear Femtosecond Processes in Liquid Phase: Water Cluster Raman Spectra and Microheterogeneity Induced Coherent Oscillations. D. Goswami, in 12th International Conference on Fiber Optics and Photonics (OSA, 2014), p. T4C.2 [Abstract] [PDF] [BibTeX]

   Abstract: Stokes region of water supercontinuum shows explicit water-cluster Raman features arising at high laser intensities. Near-infrared degenerate pump-probe of a cyanine dye shows coherent oscillations only in binary liquid mixtures at sub-40 femtosecond resolution.

    BibTeX: @inproceedings{goswamiHighlyNonlinearFemtosecond2014,
     title = {Highly {{Nonlinear Femtosecond Processes}} in {{Liquid Phase}}: {{Water Cluster Raman Spectra}} and {{Microheterogeneity Induced Coherent Oscillations}}},
     shorttitle = {Highly {{Nonlinear Femtosecond Processes}} in {{Liquid Phase}}},
     booktitle = {12th {{International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Goswami, Debabrata},
     date = {2014},
     pages = {T4C.2},
     publisher = {{OSA}},
     location = {{Kharagpur}},
     doi = {10/gf5ms5},
     url = {https://my.pcloud.com/publink/show?code=XZDGxr7ZuCkX5dqDlQ4Cww6kKhi4up5N58Wy},
     urldate = {2019-08-01},
     eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
     isbn = {978-1-55752-882-7}
   }
   

6. Quantum Distributed Computing Applied to Grover’s Search Algorithm. D. Goswami, in Computing with New Resources: Essays Dedicated to Jozef Gruska on the Occasion of His 80th Birthday, C. S. Calude, R. Freivalds, and I. Kazuo, eds., Lecture Notes in Computer Science (Springer International Publishing, 2014), pp. 192–199 [Abstract] [PDF] [BibTeX]

   Abstract: Grover’s Algorithm finds a unique element in an unsorted stock of NNN-elements in N−−√N\sqrt{N} queries through quantum search. A single-query solution can also be designed, but with an overhead of Nlog2NNlog2⁡NN\log _2 N steps to prepare and post process the query, which is worse than the classical N/2N/2N/2 queries. We show here that by distributing the computing load on a set of quantum computers, we achieve better information theoretic bounds and relaxed space scaling. Howsoever small one quantum computing node is, by virtue of networking and sharing of data, we can virtually work with a sufficiently large qubit space.

    BibTeX: @incollection{goswamiQuantumDistributedComputing2014,
     title = {Quantum {{Distributed Computing Applied}} to {{Grover}}’s {{Search Algorithm}}},
     booktitle = {Computing with {{New Resources}}: {{Essays Dedicated}} to {{Jozef Gruska}} on the {{Occasion}} of {{His}} 80th {{Birthday}}},
     author = {Goswami, Debabrata},
     editor = {Calude, Cristian S. and Freivalds, Rūsiņš and Kazuo, Iwama},
     date = {2014},
     series = {Lecture {{Notes}} in {{Computer Science}}},
     pages = {192--199},
     publisher = {{Springer International Publishing}},
     location = {{Cham}},
     url = {https://my.pcloud.com/publink/show?code=XZMGxr7Zz6GcnHs4eDHBBtjbl9pyEXfvUXhV},
     urldate = {2019-08-02},
     isbn = {978-3-319-13350-8}
   }
   

7. Effect of Molecular Structural Isomers in Thermal Lens Spectroscopy. P. Kumar, S. Dinda, and D. Goswami, Chemical Physics Letters 601, 163–167 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: We explore the importance of molecular structure on thermal lens (TL) spectroscopy by measuring the effects of molecular isomerization on TL measurements. In particular, we present a case study for all the structural isomers of butanol, namely, normal-butanol (n-BuOH), secondary-butanol (s-BuOH), isobutanol (i-BuOH) and tertiary-butanol (t-BuOH). We argue that the molecular isomerization influences the heat convection process in two possible ways: one being a change in the molecular surface area and the other being the steric hindrance. We show that n-BuOH has the highest capability to transfer heat by convection. Branching in the molecular structure renders the system sluggish as it makes the molecular motion successively retarded due to an increase in the mean free path. This we have defined as the molecular drift that slows under thermal conditions. In our studied isomers, therefore, t-BuOH drifts the slowest.

    BibTeX: @article{kumarEffectMolecularStructural2014,
     title = {Effect of Molecular Structural Isomers in Thermal Lens Spectroscopy},
     author = {Kumar, Pardeep and Dinda, Sirshendu and Goswami, Debabrata},
     date = {2014-05},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {601},
     pages = {163--167},
     issn = {00092614},
     doi = {10/gf6bk6},
     url = {https://linkinghub.elsevier.com/retrieve/pii/S0009261414002620},
     urldate = {2019-08-12}
   }
   

8. Importance of Molecular Heat Convection in Time Resolved Thermal Lens Study of Highly Absorbing Samples. P. Kumar, A. Khan, and D. Goswami, Chemical Physics 441, 5–10 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: Our experimental study shows that in the case of strongly absorbing samples, the time resolved thermal lens (TL) signal has a distinctive new feature. Existing TL models that are only based on heat conduction cannot explain this behavior. We have therefore developed a more comprehensive model that can also explain this additional feature in the TL of strongly absorbing samples. Our model is also capable of explaining our experimental results that show how the molecular size affects the molecular heat convection.

    BibTeX: @article{kumarImportanceMolecularHeat2014,
     title = {Importance of Molecular Heat Convection in Time Resolved Thermal Lens Study of Highly Absorbing Samples},
     author = {Kumar, Pardeep and Khan, Arbaz and Goswami, Debabrata},
     date = {2014-09-30},
     journaltitle = {Chemical Physics},
     shortjournal = {Chemical Physics},
     volume = {441},
     pages = {5--10},
     issn = {0301-0104},
     doi = {10/f6kr7q},
     url = {http://www.sciencedirect.com/science/article/pii/S0301010414001724},
     urldate = {2019-08-01}
   }
   

9. Importance of Molecular Structure on the Thermophoresis of Binary Mixtures. P. Kumar and D. Goswami, The Journal of Physical Chemistry B 118(51), 14852–14859 (2014) [Abstract] [PDF] [BibTeX]

   Abstract: Using thermal lens spectroscopy, we study the role of molecular structural isomers of butanol on the thermophoresis (or Soret effect) of binary mixtures of methanol in butanol. In this study, we show that the thermal lens signal due to the Soret effect changes its sign for all the different concentrations of binary mixtures of butanol with methanol except for the one containing tertiary-butanol. The magnitude and sign of the Soret coefficients strongly depend on the molecular structure of the isomers of butanol in the binary mixture with methanol. This isomerization dependence is in stark contrast to the expected mass dependence of the Soret effect.

    BibTeX: @article{kumarImportanceMolecularStructure2014,
     title = {Importance of {{Molecular Structure}} on the {{Thermophoresis}} of {{Binary Mixtures}}},
     author = {Kumar, Pardeep and Goswami, Debabrata},
     date = {2014-12-26},
     journaltitle = {The Journal of Physical Chemistry B},
     shortjournal = {J. Phys. Chem. B},
     volume = {118},
     number = {51},
     pages = {14852--14859},
     issn = {1520-6106},
     doi = {10/gf5ms6},
     url = {https://doi.org/10.1021/jp5079604},
     urldate = {2019-08-01}
   }
   

10. Unusual Behavior of Thermal Lens in Alcohols. P. Kumar, S. Dinda, A. Chakraborty, and D. Goswami, Physical Chemistry Chemical Physics 16(24), 12291–12298 (2014) [Abstract] [PDF] [BibTeX]

    Abstract: We use a femtosecond pump–probe Z-scan technique to measure the thermal lens (TL) signal in a homologous series of primary alcohols. The trend in these experimentally measured TL signals deviates in a counterintuitive manner from the ones calculated using theoretical models that are only based on the macroscopic parameters. Introspection shows that the present TL theories are based on heat conduction for low absorbing samples without considering any convective mode of heat transfer. Our studies on highly absorbing samples indicate the importance of convective mode of heat transfer in TL studies.

     BibTeX: @article{kumarUnusualBehaviorThermal2014,
      title = {Unusual Behavior of Thermal Lens in Alcohols},
      author = {Kumar, Pardeep and Dinda, Sirshendu and Chakraborty, Atanu and Goswami, Debabrata},
      date = {2014},
      journaltitle = {Physical Chemistry Chemical Physics},
      volume = {16},
      number = {24},
      pages = {12291--12298},
      doi = {10/gf5npt},
      url = {https://pubs.rsc.org/en/content/articlelanding/2014/cp/c4cp00895b},
      urldate = {2019-08-02}
    }
    

11. Graphene Oxide from Silk Cocoon: A Novel Magnetic Fluorophore for Multi-Photon Imaging. M. Roy, T. S. Kusurkar, S. K. Maurya, S. K. Meena, S. K. Singh, N. Sethy, K. Bhargava, R. K. Sharma, D. Goswami, S. Sarkar, and M. Das, 3 Biotech 4(1), 67–75 (2014) [Abstract] [PDF] [BibTeX]

    Abstract: In this work, we synthesized graphene oxide from silk cocoon embarking its new dimension as a magnetic fluorophore when compared with its present technical status, which at best is for extracting silk as a biomaterial for tissue engineering applications. We produced graphene oxide by pyrolysing the silk cocoon in an inert atmosphere. The collected raw carbon is oxidized by nitric acid that readily produces multilayer graphene oxide with nano carbon particulates. Structural properties of the graphene oxide were analyzed using scanning electron microscopy, transmission electron microscopy, Fourier transform infra-red spectroscopy, and Raman spectroscopy. The oxidized sample shows remarkable fluorescence, multi-photon imaging and magnetic properties. On increasing the excitation wavelength, the fluorescence emission intensity of the graphene oxide also increases and found maximum emission at 380 nm excitation wavelength. On studying the two photon absorption (TPA) property of aqueous graphene oxide using Z-scan technique, we found significant TPA activity at near infrared wavelength. In addition, the graphene oxide shows ferromagnetic behavior at room temperature. The observed fluorescence and magnetic property were attributed to the defects caused in the graphene oxide structure by introducing oxygen containing hydrophilic groups during the oxidation process. Previously silk cocoon has been used extensively in deriving silk-based tissue engineering materials and as gas filter. Here we show a novel application of silk cocoon by synthesizing graphene oxide based magnetic-fluorophore for bio-imaging applications.

     BibTeX: @article{royGrapheneOxideSilk2014,
      title = {Graphene Oxide from Silk Cocoon: A Novel Magnetic Fluorophore for Multi-Photon Imaging},
      shorttitle = {Graphene Oxide from Silk Cocoon},
      author = {Roy, Manas and Kusurkar, Tejas Sanjeev and Maurya, Sandeep Kumar and Meena, Sunil Kumar and Singh, Sushil Kumar and Sethy, Niroj and Bhargava, Kalpana and Sharma, Raj Kishore and Goswami, Debabrata and Sarkar, Sabyasachi and Das, Mainak},
      date = {2014-02-01},
      journaltitle = {3 Biotech},
      shortjournal = {3 Biotech},
      volume = {4},
      number = {1},
      pages = {67--75},
      issn = {2190-5738},
      doi = {10/gcb6qh},
      url = {https://doi.org/10.1007/s13205-013-0128-2},
      urldate = {2019-08-02}
    }
    

2013

1. Controlling the Femtosecond Laser-Driven Transformation of Dicyclopentadiene into Cyclopentadiene. T. Goswami, D. K. Das, and D. Goswami, Chemical Physics Letters 558, 1–7 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: Dynamics of the chemical transformation of dicyclopentadiene into cyclopentadiene in a supersonic molecular beam is elucidated using femtosecond time-resolved degenerate pump–probe mass spectrometry. Control of this ultrafast chemical reaction is achieved by using linearly chirped frequency modulated pulses. We show that negatively chirped femtosecond laser pulses enhance the cyclopentadiene photoproduct yield by an order of magnitude as compared to that of the unmodulated or the positively chirped pulses. This demonstrates that the phase structure of femtosecond laser pulse plays an important role in determining the outcome of a chemical reaction.

    BibTeX: @article{goswamiControllingFemtosecondLaserdriven2013,
     title = {Controlling the Femtosecond Laser-Driven Transformation of Dicyclopentadiene into Cyclopentadiene},
     author = {Goswami, Tapas and Das, Dipak K. and Goswami, Debabrata},
     date = {2013-02-12},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {558},
     pages = {1--7},
     issn = {0009-2614},
     doi = {10/f4nnb2},
     url = {https://my.pcloud.com/publink/show?code=XZFvxr7ZpduyXffXsJj4NXDLmSt1zLjBhELV},
     urldate = {2019-08-02}
   }
   

2. Fluorescence Advantages with Microscopic Spatiotemporal Control. D. Goswami, D. Roy, and A. K. De, in Design and Quality for Biomedical Technologies VI (International Society for Optics and Photonics, 2013), 8573, p. 857302 [Abstract] [PDF] [BibTeX]

   Abstract: We present a clever design concept of using femtosecond laser pulses in microscopy by selective excitation or de-excitation of one fluorophore over the other overlapping one. Using either a simple pair of femtosecond pulses with variable delay or using a train of laser pulses at 20-50 Giga-Hertz excitation, we show controlled fluorescence excitation or suppression of one of the fluorophores with respect to the other through wave-packet interference, an effect that prevails even after the fluorophore coherence timescale. Such an approach can be used both under the single-photon excitation as well as in the multi-photon excitation conditions resulting in effective higher spatial resolution. Such high spatial resolution advantage with broadband-pulsed excitation is of immense benefit to multi-photon microscopy and can also be an effective detection scheme for trapped nanoparticles with near-infrared light. Such sub-diffraction limit trapping of nanoparticles is challenging and a two-photon fluorescence diagnostics allows a direct observation of a single nanoparticle in a femtosecond high-repetition rate laser trap, which promises new directions to spectroscopy at the single molecule level in solution. The gigantic peak power of femtosecond laser pulses at high repetition rate, even at low average powers, provide huge instantaneous gradient force that most effectively result in a stable optical trap for spatial control at sub-diffraction limit. Such studies have also enabled us to explore simultaneous control of internal and external degrees of freedom that require coupling of various control parameters to result in spatiotemporal control, which promises to be a versatile tool for the microscopic world.

    BibTeX: @inproceedings{goswamiFluorescenceAdvantagesMicroscopic2013,
     title = {Fluorescence Advantages with Microscopic Spatiotemporal Control},
     booktitle = {Design and {{Quality}} for {{Biomedical Technologies VI}}},
     author = {Goswami, Debabrata and Roy, Debjit and De, Arijit K.},
     date = {2013-03-13},
     volume = {8573},
     pages = {857302},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/gf5npw},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8573/857302/Fluorescence-advantages-with-microscopic-spatiotemporal-control/10.1117/12.2009500.short},
     urldate = {2019-08-02},
     eventtitle = {Design and {{Quality}} for {{Biomedical Technologies VI}}}
   }
   

3. Quantum Algorithm to Solve a Maze: Converting the Maze Problem into a Search Problem. N. Kumar and D. Goswami, (2013) [Abstract] [PDF] [BibTeX]

   Abstract: We propose a different methodology towards approaching a Maze problem. We convert the problem into a Quantum Search Problem (QSP), and its solutions are sought for using the iterative Grover’s Search Algorithm. Though the category of mazes we are looking at are of the NP complete class, we have redirected such a NP complete problem into a QSP. Our solution deals with two dimensional perfect mazes with no closed loops. We encode all possible individual paths from the starting point of the maze into a quantum register. A quantum fitness operator applied on the register encodes each individual with its fitness value. We propose an oracle design which marks all the individuals above a certain fitness value and use the Grover search algorithm to find one of the marked states. Iterating over this method, we approach towards the optimum solution.

    BibTeX: @unpublished{kumarQuantumAlgorithmSolve2013,
     title = {Quantum {{Algorithm}} to {{Solve}} a {{Maze}}: {{Converting}} the {{Maze Problem}} into a {{Search Problem}}},
     shorttitle = {Quantum {{Algorithm}} to {{Solve}} a {{Maze}}},
     author = {Kumar, Niraj and Goswami, Debabrata},
     date = {2013-12-15},
     eprint = {1312.4116},
     eprinttype = {arxiv},
     eprintclass = {quant-ph},
     url = {http://arxiv.org/abs/1312.4116},
     urldate = {2019-08-02}
   }
   

4. Spectrally Resolved Photon-Echo Spectroscopy of Rhodamine-6G. A. Kumar, S. K. Karthick, and D. Goswami, Journal of spectroscopy and dynamics 3(1), 2 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: Wavelength dependent study of a laser dye: Rhodamine-6G (Rh6G) by using spectrally resolved photon-echo spectroscopy is presented. The coherence and population dynamics of Rh6G solution in methanol changes as the excitation wavelength is tuned near its absorption maxima of 528 nm. Specifically, the central wavelength of the femtosecond laser pulse was set to 535 nm and to 560 nm while the respective spectra of the photon-echo signals were collected. This gives information on how the ultrafast dynamics of the Rh6G molecule changes with a change in the excitation wavelength.

    BibTeX: @article{kumarSpectrallyResolvedPhotonecho2013,
     title = {Spectrally Resolved Photon-Echo Spectroscopy of {{Rhodamine-6G}}},
     author = {Kumar, Ajitesh and Karthick, S. K. and Goswami, D.},
     date = {2013-02},
     journaltitle = {Journal of spectroscopy and dynamics},
     shortjournal = {J Spectrosc Dyn},
     volume = {3},
     number = {1},
     eprint = {24098869},
     eprinttype = {pmid},
     pages = {2},
     issn = {2249-2704},
     url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790070/},
     urldate = {2019-08-02},
     pmcid = {PMC3790070}
   }
   

5. Real-Space Studies of the Structure and Dynamics of Self-Assembled Colloidal Clusters. R. W. Perry, G. Meng, T. G. Dimiduk, J. Fung, and V. N. Manoharan, Faraday Discussions 159(0), 211–234 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: The energetics and assembly pathways of small clusters may yield insights into processes occurring at the earliest stages of nucleation. We use a model system consisting of micrometer-sized, spherical colloidal particles to study the structure and dynamics of small clusters, where the number of particles is small (N ≤ 10). The particles interact through a short-range depletion attraction with a depth of a few kBT. We describe two methods to form colloidal clusters, one based on isolating the particles in microwells and another based on directly assembling clusters in the gas phase using optical tweezers. We use the first technique to obtain ensemble-averaged probabilities of cluster structures as a function of N. These experiments show that clusters with symmetries compatible with crystalline order are rarely formed under equilibrium conditions. We use the second technique to study the dynamics of the clusters, and in particular how they transition between free-energy minima. To monitor the clusters we use a fast three-dimensional imaging technique, digital holographic microscopy, that can resolve the positions of each particle in the cluster with 30–45 nm precision on millisecond timescales. The real-space measurements allow us to obtain estimates for the lifetimes of the energy minima and the transition states. It is not yet clear whether the observed dynamics are relevant for small nuclei, which may not have sufficient time to transition between states before other particles or clusters attach to them. However, the measurements do provide some glimpses into how systems containing a small number of particles traverse their free-energy landscape.

    BibTeX: @article{perryRealspaceStudiesStructure2013,
     title = {Real-Space Studies of the Structure and Dynamics of Self-Assembled Colloidal Clusters},
     author = {Perry, Rebecca W. and Meng, Guangnan and Dimiduk, Thomas G. and Fung, Jerome and Manoharan, Vinothan N.},
     date = {2013-03-18},
     journaltitle = {Faraday Discussions},
     shortjournal = {Faraday Discuss.},
     volume = {159},
     number = {0},
     pages = {211--234},
     issn = {1364-5498},
     doi = {10/gfv7xg},
     url = {https://pubs.rsc.org/en/content/articlelanding/2012/fd/c2fd20061a},
     urldate = {2019-10-01}
   }
   

6. Polarization Induced Control of Multiple Fluorescence from a Molecule. Chemical Physics Letters 579, 45–50 (2013) [Abstract] [PDF] [BibTeX]

   Abstract: We show novel dual fluorescent behavior of a popular indocyanine dye molecule, IR125, in dimethyl-sulfoxide solvent when excited at 527nm instead of t…

    BibTeX: @article{PolarizationInducedControl2013,
     title = {Polarization Induced Control of Multiple Fluorescence from a Molecule},
     date = {2013-07-30},
     journaltitle = {Chemical Physics Letters},
     volume = {579},
     pages = {45--50},
     issn = {0009-2614},
     doi = {10/f453dq},
     url = {https://www.sciencedirect.com/science/article/pii/S0009261413008026},
     urldate = {2019-08-02}
   }
   

2012

1. Insignificance of Relative Time Delay between Photons for a Ultrafast Two-Photon Process. A. Bose and D. Goswami, in 2012 International Conference on Fiber Optics and Photonics (PHOTONICS) (2012), pp. 1–3 [Abstract] [PDF] [BibTeX]

   Abstract: Exploring the possibility of temporally resolving dynamics in an ideal two-photon process (TPP) indicates that the existence of one-photon physical intermediate states is not a prerequisite for TPP. This study also sheds light on the phase dependence of TPP.

    BibTeX: @inproceedings{boseInsignificanceRelativeTime2012,
     title = {Insignificance of Relative Time Delay between Photons for a Ultrafast Two-Photon Process},
     booktitle = {2012 {{International Conference}} on {{Fiber Optics}} and {{Photonics}} ({{PHOTONICS}})},
     author = {Bose, A. and Goswami, D.},
     date = {2012-12},
     pages = {1--3},
     url = {http://pc.cd/pNhctalK},
     eventtitle = {2012 {{International Conference}} on {{Fiber Optics}} and {{Photonics}} ({{PHOTONICS}})}
   }
   

2. Chirp and Polarization Control of Femtosecond Molecular Fragmentation. T. Goswami, D. K. Das, S. K. Karthick Kumar, and D. Goswami, Indian Journal of Physics 86(3), 181–185 (2012) [Abstract] [PDF] [BibTeX]

   Abstract: We explore the simultaneous effect of chirp and polarization as the two control parameters for non-resonant photo-dissociation of n-propyl benzene. Experiments performed over a wide range of laser intensities show that these two control knobs behave mutually exclusively. Specifically, for the coherently enhanced fragments (C3H3 +, C5H5 +) with negatively chirped pulses and C6H5 + with positively chirped pulses, polarization effect is the same as compared to that in the case of transform-limited pulses. Though a change in polarization affects the overall fragmentation efficiency, the fragmentation pattern of n-propyl benzene molecule remains unaffected in contrast to the chirp case.

    BibTeX: @article{goswamiChirpPolarizationControl2012,
     title = {Chirp and Polarization Control of Femtosecond Molecular Fragmentation},
     author = {Goswami, T. and Das, D. K. and Karthick Kumar, S. K. and Goswami, D.},
     date = {2012-03-01},
     journaltitle = {Indian Journal of Physics},
     shortjournal = {Indian J Phys},
     volume = {86},
     number = {3},
     pages = {181--185},
     issn = {0974-9845},
     doi = {10/f3xs5c},
     url = {https://my.pcloud.com/publink/show?code=XZXvxr7ZAeDqROTwM5f4IAxCCHc87VQw2hJ7},
     urldate = {2019-08-02}
   }
   

3. Exploring Control Parameters of Two Photon Processes in Solutions. D. Goswami and A. Nag, Journal of Chemical Sciences 124(1), 281–289 (2012) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon microscopy depends extensively on the two-photon absorption cross sections of biologically relevant chromophores. High repetition rate (HRR) lasers are essential in multiphoton microscopy for generating satisfactory signal to noise at low average powers. However, HRR lasers generate thermal distortions in samples even with the slightest single photon absorption. We use an optical chopper with HRR lasers to intermittently ‘blank’ irradiation and effectively minimize thermal effects to result in a femtosecond z-scan setup that precisely measures the two-photon absorption (TPA) cross-sections of chromophores. Though several experimental factors impact such TPA measurements, a systematic effort to modulate and influence TPA characteristics is yet to evolve. Here, we present the effect of several control parameters on the TPA process that are independent of chromophore characteristics for femtosecond laser pulse based measurements; and demonstrate how the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization can become effective control parameters for such nonlinear optical properties. Open image in new window Graphical Abstract We demonstrate how, irrespective of chromophore characteristics, the femtosecond laser pulse repetition rate, chromophore environment and incident laser polarization are effective control parameters for nonlinear optical properties arising from two-photon processes.

    BibTeX: @article{goswamiExploringControlParameters2012,
     title = {Exploring Control Parameters of Two Photon Processes in Solutions},
     author = {Goswami, Debabrata and Nag, Amit},
     date = {2012-01-01},
     journaltitle = {Journal of Chemical Sciences},
     shortjournal = {J Chem Sci},
     volume = {124},
     number = {1},
     pages = {281--289},
     issn = {0973-7103},
     doi = {10/f3wxbj},
     url = {https://doi.org/10.1007/s12039-012-0227-3},
     urldate = {2019-08-02}
   }
   

4. Ultrafast Nonlinear Optical Response of Carbon Nanotubes Functionalized with Water Soluble Porphyrin. J. Gupta, C. Vijayan, S. K. Maurya, and D. Goswami, Optics Communications 285(7), 1920–1924 (2012) [Abstract] [PDF] [BibTeX]

   Abstract: A new nanocomposite is obtained by functionalizing carbon nanotubes (CNTs) with a water soluble metalloprophyrin using a simple chemical technique and characterized by optical absorption, IR, and Raman spectroscopy. Results from spectroscopic studies indicate the noncovalent nature of interaction between CNTs and porphyrin. The ultrafast nonlinear response is characterized by measuring the nonlinear absorption coefficient and refractive index by z-scan technique in the femtosecond pulse regime. The nanocomposite is found to exhibit two-photon absorption (TPA) with a reasonably large nonlinear optical coefficient, whereas pure CNTs is known to exhibit saturable absorption. Design of such water soluble nanocomposites offers scope for obtaining materials with enhanced ultrafast optical nonlinearity.

    BibTeX: @article{guptaUltrafastNonlinearOptical2012,
     title = {Ultrafast Nonlinear Optical Response of Carbon Nanotubes Functionalized with Water Soluble Porphyrin},
     author = {Gupta, Jyotsana and Vijayan, C. and Maurya, Sandeep Kumar and Goswami, D.},
     date = {2012-04-01},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {285},
     number = {7},
     pages = {1920--1924},
     issn = {0030-4018},
     doi = {10/fzw9zm},
     url = {http://www.sciencedirect.com/science/article/pii/S0030401811014532},
     urldate = {2019-08-02}
   }
   

5. Low Reynolds Number Hydrodynamics: With Special Applications to Particulate Media. J. Happel and H. Brenner, (Springer Science & Business Media, 2012) [Abstract] [BibTeX]

   Abstract: One studying the motion of fluids relative to particulate systems is soon impressed by the dichotomy which exists between books covering theoretical and practical aspects. Classical hydrodynamics is largely concerned with perfect fluids which unfortunately exert no forces on the particles past which they move. Practical approaches to subjects like fluidization, sedimentation, and flow through porous media abound in much useful but uncorrelated empirical information. The present book represents an attempt to bridge this gap by providing at least the beginnings of a rational approach to fluid particle dynamics, based on first principles. From the pedagogic viewpoint it seems worthwhile to show that the Navier-Stokes equations, which form the basis of all systematic texts, can be employed for useful practical applications beyond the elementary problems of laminar flow in pipes and Stokes law for the motion of a single particle. Although a suspension may often be viewed as a continuum for practical purposes, it really consists of a discrete collection of particles immersed in an essentially continuous fluid. Consideration of the actual detailed boundary value problems posed by this viewpoint may serve to call attention to the limitation of idealizations which apply to the overall transport properties of a mixture of fluid and solid particles.

    BibTeX: @book{happelLowReynoldsNumber2012,
     title = {Low {{Reynolds}} Number Hydrodynamics: With Special Applications to Particulate Media},
     shorttitle = {Low {{Reynolds}} Number Hydrodynamics},
     author = {Happel, J. and Brenner, H.},
     date = {2012-12-06},
     publisher = {{Springer Science \& Business Media}},
     isbn = {978-94-009-8352-6},
     pagetotal = {564}
   }
   

6. Study of Self Defocusing in Liquids Using Single Beam Z-scan with High Repetition Rate Laser Pulses. S. K. Maurya, S. Singhal, and D. Goswami, in International Conference on Fibre Optics and Photonics (OSA, 2012), p. TPo.44 [Abstract] [PDF] [BibTeX]

   Abstract: We report the behavior of nonlinear refraction property of solvent using femtosecond high repetition rate laser pulses with close aperture z scan technique. Self defocusing due to HRR pulses highly depend on viscosity and density of the systems.

    BibTeX: @inproceedings{mauryaStudySelfDefocusing2012,
     title = {Study of Self Defocusing in Liquids Using Single Beam {{Z-scan}} with {{High}} Repetition Rate Laser Pulses},
     booktitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}},
     author = {Maurya, Sandeep Kumar and Singhal, Sumit and Goswami, Debabrata},
     date = {2012},
     pages = {TPo.44},
     publisher = {{OSA}},
     location = {{Chennai}},
     doi = {10/gf5nqb},
     url = {https://www.osapublishing.org/abstract.cfm?URI=Photonics-2012-TPo.44},
     urldate = {2019-08-02},
     eventtitle = {International {{Conference}} on {{Fibre Optics}} and {{Photonics}}}
   }
   

7. Effect of Linear Chirp on Femtosecond Two-Photon Processes in Solution. A. Nag and D. Goswami, Journal of spectroscopy and dynamics 2(3), (2012) [Abstract] [PDF] [BibTeX]

   Abstract: Coherent control via linear chirping a femtosecond laser pulse holds the promise of a potent spectroscopic tool in the study of two-photon processes in condensed phase. Here, we show modulation in the two-photon absorption and fluorescence of several common dyes in solution by simple phase ordering of femtosecond laser pulse into a linearly frequency chirped pulse. However, the modulation is dependent on associated solvent properties as the coherence is lost rapidly in the solution phase. Also, systematic effects are mostly seen only over a limited range of chirp since it is an interplay of two opposing effects on two-photon processes—linear chirp enhancing it while the associated pulse broadening reducing it.

    BibTeX: @article{nagEffectLinearChirp2012,
     title = {Effect of Linear Chirp on Femtosecond Two-Photon Processes in Solution},
     author = {Nag, Amit and Goswami, Debabrata},
     date = {2012-08-31},
     journaltitle = {Journal of spectroscopy and dynamics},
     shortjournal = {J Spectrosc Dyn},
     volume = {2},
     number = {3},
     eprint = {24364002},
     eprinttype = {pmid},
     issn = {2249-2704},
     url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3868930/},
     urldate = {2019-08-02},
     pmcid = {PMC3868930}
   }
   

2011

1. Probing Intermolecular Interaction through Thermal-Lens Spectroscopy. I. Bhattacharyya, P. Kumar, and D. Goswami, The Journal of Physical Chemistry B 115(2), 262–268 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Binary liquid mixtures are studied using femtosecond pump−probe thermal-lens (TL) spectroscopy. Changes in the measured TL signals as a function of relative concentration of binary mixtures show that these result from a combined effect of physical and molecular properties of the constituent binary liquids. The experimental TL values deviate from the ones calculated from phenomenological equations. These, we argue, are due to an underestimation of the influence of molecular interactions when the TL signals are calculated by using physical parameters only.

    BibTeX: @article{bhattacharyyaProbingIntermolecularInteraction2011,
     title = {Probing {{Intermolecular Interaction}} through {{Thermal-Lens Spectroscopy}}},
     author = {Bhattacharyya, Indrajit and Kumar, Pardeep and Goswami, Debabrata},
     date = {2011-01-20},
     journaltitle = {The Journal of Physical Chemistry B},
     shortjournal = {J. Phys. Chem. B},
     volume = {115},
     number = {2},
     pages = {262--268},
     issn = {1520-6106},
     doi = {10/d9mz5f},
     url = {https://doi.org/10.1021/jp1062429},
     urldate = {2019-08-14}
   }
   

2. Two-Photon-Absorption Technique for Selective Detection of Copper(II) Ions in Aqueous Solution Using a Dansyl–Pyrene Conjugate. V. Chandrasekhar, M. D. Pandey, S. K. Maurya, P. Sen, and D. Goswami, Chemistry – An Asian Journal 6(9), 2246–2250 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Rhythm is a dansyl: A novel dansyl–pyrene conjugate functions as a fluorescence signaling unit showing strong fluorescence quenching upon interaction with copper(II) metal ions. On the other hand, the two-photon absorption (TPA) cross-section increased from 374 to 3022 GM (at 770 nm) upon interaction with copper(II) ions, thus allowing their selective detection in aqueous solutions.

    BibTeX: @article{chandrasekharTwoPhotonAbsorptionTechniqueSelective2011,
     title = {Two-{{Photon-Absorption Technique}} for {{Selective Detection}} of {{Copper}}({{II}}) {{Ions}} in {{Aqueous Solution Using}} a {{Dansyl}}–{{Pyrene Conjugate}}},
     author = {Chandrasekhar, Vadapalli and Pandey, Mrituanjay D. and Maurya, Sandeep Kumar and Sen, Pratik and Goswami, Debabrata},
     date = {2011},
     journaltitle = {Chemistry – An Asian Journal},
     volume = {6},
     number = {9},
     pages = {2246--2250},
     issn = {1861-471X},
     doi = {10/c5ft2w},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/asia.201100032},
     urldate = {2019-08-02}
   }
   

3. Control of Femtosecond Laser Driven Retro-Diels-Alder-like Reaction of Dicyclopentadiene. D. K. Das, T. Goswami, and D. Goswami, in Photonics 2010: Tenth International Conference on Fiber Optics and Photonics (International Society for Optics and Photonics, 2011), 8173, p. 81730O [Abstract] [PDF] [BibTeX]

   Abstract: Using femtosecond time resolved degenerate pump-probe mass spectrometry coupled with simple linearly chirped frequency modulated pulse, we elucidate that the dynamics of retro-Diels-Alder reaction of diclopentadiene (DCPD) to cyclopentadiene (CPD) in supersonic molecular beam occurs in ultrafast time scale. Negatively chirped pulse enhances the ion yield of CPD, as compared to positively chirped pulse. This indicates that by changing the frequency (chirp) of the laser pulse we can control the ion yield of a chemical reaction.

    BibTeX: @inproceedings{dasControlFemtosecondLaser2011,
     title = {Control of Femtosecond Laser Driven Retro-{{Diels-Alder-like}} Reaction of Dicyclopentadiene},
     booktitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}},
     author = {Das, Dipak Kumar and Goswami, Tapas and Goswami, Debabrata},
     date = {2011-08-23},
     volume = {8173},
     pages = {81730O},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/dsc8s7},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8173/81730O/Control-of-femtosecond-laser-driven-retro-Diels-Alder-like-reaction/10.1117/12.897909.short},
     urldate = {2019-08-13},
     eventtitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}}
   }
   

4. Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping: A Spatiotemporal Approach. A. K. De and D. Goswami, International Reviews in Physical Chemistry 30(3), 275–299 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: This account reviews some recent studies pursued in our group on several control experiments with important applications in (one-photon) confocal and two-photon fluorescence laser-scanning microscopy and optical trapping with laser tweezers. We explore the simultaneous control of internal and external (i.e. centre-of-mass motion) degrees of freedom, which require the coupling of various control parameters to result in the spatiotemporal control. Of particular interest to us is the implementation of such control schemes in living systems. A live cell is a system of a large number of different molecules which combine and interact to generate complex structures and functions. These combinations and interactions of molecules need to be choreographed perfectly in time and space to achieve intended intra-cellular functions. Spatiotemporal control promises to be a versatile tool for dynamical control of spatially manipulated bio-molecules.

    BibTeX: @article{deControllingMolecularMotions2011,
     title = {Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping: A Spatiotemporal Approach},
     shorttitle = {Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2011-07-01},
     journaltitle = {International Reviews in Physical Chemistry},
     volume = {30},
     number = {3},
     pages = {275--299},
     issn = {0144-235X},
     doi = {10/fmhbzc},
     url = {https://doi.org/10.1080/0144235X.2011.603237},
     urldate = {2019-08-13}
   }
   

5. Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy. A. K. De, D. Roy, and D. Goswami, Physical Review A 83(1), 015402 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: We show fluorescence-detected quantum interference in a microscope setup and demonstrate selective enhancement or suppression of fluorophores using femtosecond pulse-pair excitation with periodic modulation of the interpulse phase.

    BibTeX: @article{deFluorophoreDiscriminationTracing2011,
     title = {Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2011-01-21},
     journaltitle = {Physical Review A},
     shortjournal = {Phys. Rev. A},
     volume = {83},
     number = {1},
     pages = {015402},
     doi = {10/c73nhs},
     url = {https://link.aps.org/doi/10.1103/PhysRevA.83.015402},
     urldate = {2019-08-14}
   }
   

6. Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission. A. K. De, D. Roy, and D. Goswami, Journal of Biomedical Optics 16(10), 100505 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Controlling two-photon molecular fluorescence leading to selective fluorophore excitation has been a long sought after goal in fluorescence microscopy. In this letter, we thoroughly explore selective fluorescence suppression through simultaneous two-photon absorption by two different fluorophores followed by selective one-photon stimulated emission for one particular fluorophore. We achieve this by precisely controlling the time delay between two identical ultrafast near infrared laser pulses.

    BibTeX: @article{deSelectiveTwophotonFluorescence2011,
     title = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission},
     shorttitle = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation},
     author = {De, Arijit K. and Roy, Debjit and Goswami, Debabrata},
     date = {2011-10},
     journaltitle = {Journal of Biomedical Optics},
     shortjournal = {JBO},
     volume = {16},
     number = {10},
     pages = {100505},
     issn = {1083-3668, 1560-2281},
     doi = {10/fqkzpp},
     url = {https://my.pcloud.com/publink/show?code=XZoNxr7Zgv99AAhjLt4lAwzfutsBwYsdJNvy},
     urldate = {2019-08-02}
   }
   

7. Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers. A. K. De, D. Roy, and D. Goswami, CURRENT SCIENCE 101(7), 4 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: We show how two-photon fluorescence signal can be used as an effective detection scheme for trapping particles of any size in comparison to methods using back-scattered light. Development of such a diagnostic scheme allows us a direct observation of trapping a single nanoparticle, which shows new directions to spectroscopy at the single-molecule level in solution.

    BibTeX: @article{deTwophotonFluorescenceDiagnostics2011,
     title = {Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2011},
     journaltitle = {CURRENT SCIENCE},
     volume = {101},
     number = {7},
     pages = {4},
     url = {https://my.pcloud.com/publink/show?code=XZyaxr7ZQuCnGQH0PFBeRMoMq6mRURASwEJk}
   }
   

8. Towards Using Molecular States as Qubits. D. Goswami, T. Goswami, S. K. K. Kumar, and D. K. Das, AIP Conference Proceedings 1384(1), 251–253 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Molecular systems are presented as possible qubit systems by exploring non‐resonant molecular fragmentation of n‐propyl benzene with femtosecond laser pulses as a model case. We show that such laser fragmentation process is dependent on the phase and polarization characteristics of the laser. The effect of the chirp and polarization of the femtosecond pulse when applied simultaneously is mutually independent of each other, which makes chirp and polarization as useful ‘logic’ implementing parameters for such molecular qubits.

    BibTeX: @article{goswamiUsingMolecularStates2011,
     title = {Towards {{Using Molecular States}} as {{Qubits}}},
     author = {Goswami, Debabrata and Goswami, Tapas and Kumar, S. K. Karthick and Das, Dipak K.},
     date = {2011-09-23},
     journaltitle = {AIP Conference Proceedings},
     shortjournal = {AIP Conference Proceedings},
     volume = {1384},
     number = {1},
     pages = {251--253},
     issn = {0094-243X},
     doi = {10/bfnp4m},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.3635869},
     urldate = {2019-08-02}
   }
   

9. An Efficient Nanocomposite Based on Carbon Nanotubes Functionalized with a Fluorescent Ink for Ultrafast Optical Limiting. J. Gupta, C. Vijayan, S. K. Maurya, and D. Goswami, Materials Letters 65(5), 915–917 (2011) [Abstract] [PDF] [BibTeX]

   Abstract: Functionalization of CNTs with different kinds of molecules is known to alter the optical properties of CNTs, leading to the development of new nanocomposites of interest to optoelctronics. This paper presents the design of a new and efficient optical limiting material based on carbon nanotubes (CNTs) functionalized with a commercial fluorescent ink. High resolution transmission electron microscopy (HRTEM) and optical spectroscopy indicate that the ink molecules get noncovalently attached to the surface of the CNTs. The mechanism of optical nonlinearity of the CNTs gets modified after functionalization. Z-scan studies on functionalized CNTs performed using mode-locked Ti:Sapphire femtosecond pulses at 780nm reveal the predominance of two photon absorption (TPA). Efficient and low threshold ultrafast optical limiting is demonstrated in the new nanocomposite.

    BibTeX: @article{guptaEfficientNanocompositeBased2011,
     title = {An Efficient Nanocomposite Based on Carbon Nanotubes Functionalized with a Fluorescent Ink for Ultrafast Optical Limiting},
     author = {Gupta, Jyotsana and Vijayan, C. and Maurya, Sandeep Kumar and Goswami, D.},
     date = {2011-03-15},
     journaltitle = {Materials Letters},
     shortjournal = {Materials Letters},
     volume = {65},
     number = {5},
     pages = {915--917},
     issn = {0167-577X},
     doi = {10/cd5dqh},
     url = {http://www.sciencedirect.com/science/article/pii/S0167577X10010554},
     urldate = {2019-08-13}
   }
   

10. Efficient Ultrafast Optical Limiting Using Single Walled Carbon Nanotubes Functionalized Noncovalently with Free Base and Metalloporphyrins. J. Gupta, C. Vijayan, S. K. Maurya, and D. Goswami, Journal of Applied Physics 109(11), 113101 (2011) [Abstract] [PDF] [BibTeX]

    Abstract: The present work is on the linear and third order nonlinear optical properties of single walled carbon nanotubes functionalized noncovalently with free base porphyrin and a metalloporphyrin separately. The functionalized carbon nanotubes (CNTs) are soluble in dimethylformamide, and the microscopic images show that the porphyrin molecules are attached to the surface of the CNTs. The interaction between CNTs and porphyrins is noncovalent and probably due to π-π interaction as both CNTs and porphyrins have π-electron rich structures. The samples exhibit large ultrafast nonlinear absorption as evident from the open aperture z-scan studies performed using mode-locked Ti:Sapphire femtosecond pulses at 780 nm. The mechanisms of optical nonlinearity of the functionalized CNTs appear to be two photon absorption along with nonlinear scattering with a small contribution from saturable absorption, whereas nonfunctionalized CNTs are known to exhibit saturable absorption. The value of the nonlinear absorption coefficient for the CNTs functionalized with the free base porphyrin is one order smaller than that for CNTs functionalized with metalloporphyrin. Efficient low threshold ultrafast optical limiting is demonstrated for both types of functionalized CNTs.

     BibTeX: @article{guptaEfficientUltrafastOptical2011,
      title = {Efficient Ultrafast Optical Limiting Using Single Walled Carbon Nanotubes Functionalized Noncovalently with Free Base and Metalloporphyrins},
      author = {Gupta, Jyotsana and Vijayan, C. and Maurya, Sandeep Kumar and Goswami, D.},
      date = {2011-06},
      journaltitle = {Journal of Applied Physics},
      shortjournal = {Journal of Applied Physics},
      volume = {109},
      number = {11},
      pages = {113101},
      issn = {0021-8979, 1089-7550},
      doi = {10/cx5v4x},
      url = {http://aip.scitation.org/doi/10.1063/1.3587178},
      urldate = {2019-08-13}
    }
    

11. Structure and Hydrogen Bond Vibrations of the Jet-Cooled 1:1 Complex between 7-Azaindole and Formamide: A Laser-Induced Fluorescence Spectroscopy Study. M. K. Hazra, M. Mukherjee, D. Goswami, and T. Chakraborty, Chemical Physics Letters 503(4), 203–209 (2011) [Abstract] [PDF] [BibTeX]

    Abstract: Laser-induced fluorescence spectra of 7-azaindole⋯formamide complex are measured in a supersonic free jet expansion. Calculation at MP2/6-311++G∗∗ level predicts a cyclic doubly hydrogen-bonded structure for the complex is favoured most in the ground state. The complex emits only UV fluorescence from the locally excited state and tautomerization is inhibited under the jet-cooled environment. This photophysical behavior is consistent with the predictions of CIS/6-311++G∗∗ and TDDFT/6-311++G∗∗ calculations. The low-frequency bands in the fluorescence spectra are assigned to different hydrogen bond modes of the complex, and the spectra reveal signatures of mixing between inter- and intra-molecular vibrational modes in the excited state.

     BibTeX: @article{hazraStructureHydrogenBond2011,
      title = {Structure and Hydrogen Bond Vibrations of the Jet-Cooled 1:1 Complex between 7-Azaindole and Formamide: {{A}} Laser-Induced Fluorescence Spectroscopy Study},
      shorttitle = {Structure and Hydrogen Bond Vibrations of the Jet-Cooled 1},
      author = {Hazra, Montu K. and Mukherjee, Moitrayee and Goswami, Debabrata and Chakraborty, Tapas},
      date = {2011-02-17},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {503},
      number = {4},
      pages = {203--209},
      issn = {0009-2614},
      doi = {10/bj9kdz},
      url = {http://www.sciencedirect.com/science/article/pii/S000926141100025X},
      urldate = {2019-08-13}
    }
    

12. Microscopic Probing of Two-Photon Fluorescence for Cancer Diagnosis. A. Kumar De, N. N. Mutyal, and D. Goswami, Current science 100(3), 294–295 (2011) [Abstract] [PDF] [BibTeX]

    Abstract: For decades, molecular fluorescence-based microscopic methods have been a standard tool for wide-ranging biological applications1. Many molecules within the live cell (e.g. amino acids like tryptophan and tyrosine, riboflavins, nicotinamides, etc.) are fluorescent by themselves, and therefore are potential candidates to be probed using fluorescence microscopy. This phenomenon of intrinsic fluorescence is known as ‘auto-fluorescence’. Amongst various fluorescence-based imaging techniques, multi-photon fluorescence microscopy2,3 has been shown to be an excellent candidate for quantitative auto-fluorescence detection. Recently, it has been demonstrated that multi-photon excited auto-fluorescence can be a significant marker for cancer4,5. Here we describe the salient features of a multiphoton fluorescence microscope constructed in our laboratory and report its potential applications in cancer diagnosis.

     BibTeX: @article{kumardeMicroscopicProbingTwophoton2011,
      title = {Microscopic Probing of Two-Photon Fluorescence for Cancer Diagnosis},
      author = {Kumar De, Arijit and Mutyal, Nikhil N. and Goswami, Debabrata},
      date = {2011-02-10},
      journaltitle = {Current science},
      shortjournal = {Curr Sci},
      volume = {100},
      number = {3},
      eprint = {23814312},
      eprinttype = {pmid},
      pages = {294--295},
      issn = {0011-3891},
      url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3695547/},
      urldate = {2019-08-14},
      pmcid = {PMC3695547}
    }
    

13. Spectrally Resolved Femtosecond Photon Echo Spectroscopy of Astaxanthin. A. Kumar, S. K. K. Kumar, A. Gupta, and D. Goswami, in Photonics 2010: Tenth International Conference on Fiber Optics and Photonics (International Society for Optics and Photonics, 2011), 8173, p. 817325 [Abstract] [PDF] [BibTeX]

    Abstract: We have studied the coherence and population dynamics of Astaxanthin solution in methanol and acetonitrile by spectrally resolving their photon echo signals. Our experiments indicate that methanol has a much stronger interaction with the ultrafast dynamics of Astaxanthin in comparison to that of acetonitrile.

     BibTeX: @inproceedings{kumarSpectrallyResolvedFemtosecond2011,
      title = {Spectrally Resolved Femtosecond Photon Echo Spectroscopy of Astaxanthin},
      booktitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      author = {Kumar, Ajitesh and Kumar, S. K. Karthick and Gupta, Aditya and Goswami, Debabrata},
      date = {2011-08-23},
      volume = {8173},
      pages = {817325},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/fs3jxj},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8173/817325/Spectrally-resolved-femtosecond-photon-echo-spectroscopy-of-astaxanthin/10.1117/12.899781.short},
      urldate = {2019-08-02},
      eventtitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}}
    }
    

14. Thermal-Lens Spectroscopy in Binary Liquids Mixtures: Effect of Isotope Substitution. P. Kumar, I. Bhattacharyya, and D. Goswami, in Frontiers in Optics 2011/Laser Science XXVII (2011), Paper JTuA25 (Optical Society of America, 2011), p. JTuA25 [Abstract] [PDF] [BibTeX]

    Abstract: Using femtosecond pump-probe thermal lens (TL) spectroscopy, we show that the effect of isotope substitution can be monitored through a modulation of TL signals in binary liquids showing the important of molecular properties on TL.

     BibTeX: @inproceedings{kumarThermalLensSpectroscopyBinary2011,
      title = {Thermal-{{Lens Spectroscopy}} in {{Binary Liquids Mixtures}}: {{Effect}} of {{Isotope Substitution}}},
      shorttitle = {Thermal-{{Lens Spectroscopy}} in {{Binary Liquids Mixtures}}},
      booktitle = {Frontiers in {{Optics}} 2011/{{Laser Science XXVII}} (2011), Paper {{JTuA25}}},
      author = {Kumar, Pardeep and Bhattacharyya, Indrajit and Goswami, Debabrata},
      date = {2011-10-16},
      pages = {JTuA25},
      publisher = {{Optical Society of America}},
      doi = {10/gf5nqg},
      url = {https://www.osapublishing.org/abstract.cfm?uri=FiO-2011-JTuA25},
      urldate = {2019-08-02},
      eventtitle = {Frontiers in {{Optics}}}
    }
    

15. Polarization Modulated Ultrafast Pulse-Pair Control in Two-Photon Fluorescence Microscopy. D. Roy, A. K. De, and D. Goswami, in Frontiers in Optics 2011/Laser Science XXVII (OSA, 2011), p. JWA3 [Abstract] [PDF] [BibTeX]

    Abstract: Selective fluorescence suppression for two spectrally overlapping fluorophores that undergo simultaneous two-photon absorption from identical femtosecond pulses through precise control in relative timing and polarization of the exciting pulse-pair.

     BibTeX: @inproceedings{royPolarizationModulatedUltrafast2011,
      title = {Polarization Modulated {{Ultrafast Pulse-Pair Control}} in {{Two-Photon Fluorescence Microscopy}}},
      booktitle = {Frontiers in {{Optics}} 2011/{{Laser Science XXVII}}},
      author = {Roy, Debjit and De, Arijit Kumar and Goswami, Debabrata},
      date = {2011},
      pages = {JWA3},
      publisher = {{OSA}},
      location = {{San Jose, California}},
      doi = {10/gf5nqh},
      url = {https://www.osapublishing.org/abstract.cfm?URI=FiO-2011-JWA3},
      urldate = {2019-08-02},
      eventtitle = {Frontiers in {{Optics}}},
      isbn = {978-1-55752-917-6}
    }
    

2010

1. Decoding Coherent Information in Femtosecond Shaped Laser Pulses. I. Bhattacharyya, A. Dutta, S. Ashtekar, S. K. Maurya, and D. Goswami, CURRENT SCIENCE 99(4), 10 (2010) [Abstract] [BibTeX]

   Abstract: We report here an experimental demonstration of a pulse decoding technique from spectral analysis of femtosecond pulses. This technique is based on a single-step Fourier domain inversion algorithm and shows the impact of the spectral window function on the retrieval of the signal pulse. Using two femtosecond laser pulses at 780 and 1560 nm from a fibre laser, we have shown that even when the spectral content of the reference pulse is far from a narrow band limit (as much as a quarter of its entire spectral content for our conditions), the single-step retrieval analysis using spectral windowing in the Fourier domain works efficiently. The enhanced signal levels possible due to the wider spectral window are critical in the unambiguous description of laser pulses, which would have potential application in the retrieval of comparatively weak and complex ultra-short pulses as is often needed in pulse shaping applications and coherent optical communications.

    BibTeX: @article{bhattacharyyaDecodingCoherentInformation2010,
     title = {Decoding Coherent Information in Femtosecond Shaped Laser Pulses},
     author = {Bhattacharyya, Indrajit and Dutta, Aveek and Ashtekar, Sumit and Maurya, Sandeep Kumar and Goswami, Debabrata},
     date = {2010},
     journaltitle = {CURRENT SCIENCE},
     volume = {99},
     number = {4},
     pages = {10}
   }
   

2. Thermal-Lens Spectroscopy in Binary Liquids Mixtures. I. Bhattacharyya, P. Kumar, and D. Goswami, in Frontiers in Optics 2010/Laser Science XXVI (2010), Paper FWX1 (Optical Society of America, 2010), p. FWX1 [Abstract] [PDF] [BibTeX]

   Abstract: Using femtosecond pump-probe thermal-lens (TL) spectroscopy, experiments in binary-mixtures are presented where trends in TL are modulated by physical and molecular properties. Deviations of experimental results from phenomenological models indicate possible underestimation of molecular interactions.

    BibTeX: @inproceedings{bhattacharyyaThermalLensSpectroscopyBinary2010,
     title = {Thermal-{{Lens}} Spectroscopy in Binary Liquids Mixtures},
     booktitle = {Frontiers in {{Optics}} 2010/{{Laser Science XXVI}} (2010), Paper {{FWX1}}},
     author = {Bhattacharyya, Indrajit and Kumar, Pardeep and Goswami, Debabrata},
     date = {2010-10-24},
     pages = {FWX1},
     publisher = {{Optical Society of America}},
     doi = {10/gf6c8z},
     url = {https://www.osapublishing.org/abstract.cfm?uri=FiO-2010-FWX1},
     urldate = {2019-08-14},
     eventtitle = {Frontiers in {{Optics}}}
   }
   

3. Synthesis, Structure, and Two-Photon Absorption Studies of a Phosphorus-Based Tris Hydrazone Ligand (S)P[N(Me)N═CH-C6H3-2-OH-4-N(CH2CH3)2]3 and Its Metal Complexes. V. Chandrasekhar, R. Azhakar, B. Murugesapandian, T. Senapati, P. Bag, M. D. Pandey, S. K. Maurya, and D. Goswami, Inorganic Chemistry 49(9), 4008–4016 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: A phosphorus-supported multidentate ligand (S)P[N(Me)N═CH-C6H3-2-OH-4-N(CH 2CH3)2]3 (1) has been used to prepare mononuclear complexes LM [M = Fe (2) Co (3)] and trinuclear complexes L2M3 [M = Mn (4), Ni (5), Zn (6), Mg (7), Cd (8)]. In both 2 and 3 the ligand binds the metal ion in a facial coordination mode utilizing three imino nitrogen (3N) and three phenolic oxygen (3O) atoms. The molecular structures of L2Mn3, L2Ni3, L2Zn3, L2Mg3, and L2Cd3 (4−8) are similar; two trihydrazone ligands are involved in coordination to hold the three metal ions in a linear fashion. Each of the trishydrazone ligands behaves as a trianionic hexadentate ligand providing three imino and three phenolic oxygen atoms for coordination to the metal ions. The coordination environment around the two terminal metal ions is similar (3N, 3O) while the central metal ion has a 6O coordination environment. Third-order non-linear optical properties of these compounds as measured by their two-photon absorption (TPA) cross section reveals that while 1 does not possess obvious TPA activity, complexes 2 (3213 GM) and 4 (3516 GM) possess a large TPA cross section at 770 nm.

    BibTeX: @article{chandrasekharSynthesisStructureTwoPhoton2010,
     title = {Synthesis, {{Structure}}, and {{Two-Photon Absorption Studies}} of a {{Phosphorus-Based Tris Hydrazone Ligand}} ({{S}}){{P}}[{{N}}({{Me}}){{N}}═{{CH-C6H3-2-OH-4-N}}({{CH2CH3}})2]3 and {{Its Metal Complexes}}},
     author = {Chandrasekhar, Vadapalli and Azhakar, Ramachandran and Murugesapandian, Balasubramanian and Senapati, Tapas and Bag, Prasenjit and Pandey, Mrituanjay D. and Maurya, Sandeep Kumar and Goswami, Debabrata},
     date = {2010-05-03},
     journaltitle = {Inorganic Chemistry},
     shortjournal = {Inorg. Chem.},
     volume = {49},
     number = {9},
     pages = {4008--4016},
     issn = {0020-1669},
     doi = {10/bvqgfp},
     url = {https://doi.org/10.1021/ic901531e},
     urldate = {2019-08-14}
   }
   

4. Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation. A. K. De, D. Roy, and D. Goswami, Journal of Biomedical Optics 15(6), 060502 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: Selective excitation of a particular fluorophore in the presence of others demands clever design of the optical field interacting with the molecules. We describe the use of 20- to 50-GHz pulse-train excitation leading to two-photon absorption, followed by successive one-photon stimulated emission as a potential technique in the context of controlling two-photon molecular fluorescence, with applications in microscopy.

    BibTeX: @article{deSelectiveSuppressionTwophoton2010,
     title = {Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2010-11},
     journaltitle = {Journal of Biomedical Optics},
     shortjournal = {JBO},
     volume = {15},
     number = {6},
     pages = {060502},
     issn = {1083-3668, 1560-2281},
     doi = {10/cp9rx2},
     url = {https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-15/issue-6/060502/Selective-suppression-of-two-photon-fluorescence-in-laser-scanning-microscopy/10.1117/1.3509383.short},
     urldate = {2019-08-14}
   }
   

5. Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De, D. Roy, and D. Goswami, in Multiphoton Microscopy in the Biomedical Sciences X (International Society for Optics and Photonics, 2010), 7569, p. 756929 [Abstract] [PDF] [BibTeX]

   Abstract: The broad spectral window of an ultra-short laser pulse and the broad overlapping multiphoton absorption spectra of common fluorophores restrict selective excitation of one fluorophore in presence of others during multiphoton fluorescence microscopy. Also spatial resolution, limited by the fundamental diffraction limit, is governed by the beam profile. Here we show our recent work on selective fluorescence suppression using a femtosecond pulse-pair excitation which is equivalent to amplitude shaping using a pulse shaper. In addition, prospects of laser beam shaping in imaging are also briefly discussed.

    BibTeX: @inproceedings{deSpatiotemporalControlMultiphoton2010,
     title = {Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
     booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2010-02-26},
     volume = {7569},
     pages = {756929},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/c529hw},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7569/756929/Spatio-temporal-control-in-multiphoton-fluorescence-laser-scanning-microscopy/10.1117/12.838287.short},
     urldate = {2019-08-14},
     eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}}
   }
   

6. Towards Stable Trapping of Single Macromolecules in Solution. A. K. De, D. Roy, and D. Goswami, in Optical Trapping and Optical Micromanipulation VII (International Society for Optics and Photonics, 2010), 7762, p. 776203 [Abstract] [PDF] [BibTeX]

   Abstract: The implementation of high instantaneous peak power of a femtosecond laser pulse at moderate time-averaged power (~10 mW) to trap latex nanoparticles, which is otherwise impossible with continuous wave illumination at similar power level, has recently been shown [De, A. K., Roy, D., Dutta, A. and Goswami, D. "Stable optical trapping of latex nanoparticles with ultrashort pulsed illumination", Appd. Opt., 48, G33 (2009)]. However, direct measurement of the instantaneous trapping force/stiffness due to a single pulse has been unsuccessful due to the fleeting existence (~100 fs) of the laser pulse compared with the much slower time scale associated with the available trapping force/stiffness calibration techniques, as discussed in this proceeding article. We also demonstrate trapping of quantum dots having dimension similar to macromolecules.

    BibTeX: @inproceedings{deStableTrappingSingle2010,
     title = {Towards Stable Trapping of Single Macromolecules in Solution},
     booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}},
     author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata},
     date = {2010-08-27},
     volume = {7762},
     pages = {776203},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/ckqvtz},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7762/776203/Towards-stable-trapping-of-single-macromolecules-in-solution/10.1117/12.862364.short},
     urldate = {2019-08-14},
     eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}}
   }
   

7. Optical Trapping with High Forces Reveals Unexpected Behaviors of Prion Fibrils. J. Dong, C. E. Castro, M. C. Boyce, M. J. Lang, and S. Lindquist, Nature Structural & Molecular Biology 17(12), 1422–1430 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: Amyloid fibrils feature in many human diseases and in epigenetic memory, but understanding their molecular structure has been difficult. Now, through a combination of optical trapping and fluorescent imaging to examine amyloid fibrils of the yeast prion protein Sup35, the unexpected unfolding of individual subdomains has been detected, suggesting strong noncovalent interactions maintain the fibril even if individual monomers unfold.

    BibTeX: @article{dongOpticalTrappingHigh2010,
     title = {Optical Trapping with High Forces Reveals Unexpected Behaviors of Prion Fibrils},
     author = {Dong, Jijun and Castro, Carlos E. and Boyce, Mary C. and Lang, Matthew J. and Lindquist, Susan},
     date = {2010-12},
     journaltitle = {Nature Structural \& Molecular Biology},
     shortjournal = {Nat Struct Mol Biol},
     volume = {17},
     number = {12},
     pages = {1422--1430},
     issn = {1545-9985},
     doi = {10/cwz3hf},
     url = {https://www.nature.com/articles/nsmb.1954},
     urldate = {2019-10-01}
   }
   

8. Aggregation-Disaggregation Transition of DNA-coated Colloids: Experiments and Theory. R. Dreyfus, Physical Review E 81(4), (2010) [BibTeX]

    BibTeX: @article{dreyfusAggregationdisaggregationTransitionDNAcoated2010,
     title = {Aggregation-Disaggregation Transition of {{DNA-coated}} Colloids: {{Experiments}} and Theory},
     shorttitle = {Aggregation-Disaggregation Transition of {{DNA-coated}} Colloids},
     author = {Dreyfus, Rémi},
     date = {2010},
     journaltitle = {Physical Review E},
     shortjournal = {Phys. Rev. E},
     volume = {81},
     number = {4},
     doi = {10/dv9dh3}
   }
   

9. Self-Assembled Plasmonic Nanoparticle Clusters. J. A. Fan, C. Wu, K. Bao, J. Bao, R. Bardhan, N. J. Halas, V. N. Manoharan, P. Nordlander, G. Shvets, and F. Capasso, Science 328(5982), 1135–1138 (2010) [Abstract] [PDF] [BibTeX]

   Abstract: The self-assembly of colloids is an alternative to top-down processing that enables the fabrication of nanostructures. We show that self-assembled clusters of metal-dielectric spheres are the basis for nanophotonic structures. By tailoring the number and position of spheres in close-packed clusters, plasmon modes exhibiting strong magnetic and Fano-like resonances emerge. The use of identical spheres simplifies cluster assembly and facilitates the fabrication of highly symmetric structures. Dielectric spacers are used to tailor the interparticle spacing in these clusters to be approximately 2 nanometers. These types of chemically synthesized nanoparticle clusters can be generalized to other two- and three-dimensional structures and can serve as building blocks for new metamaterials. A hierarchy of nanoscale optical structures is created from nanoparticles that have metal shells and dielectric cores. A hierarchy of nanoscale optical structures is created from nanoparticles that have metal shells and dielectric cores.

    BibTeX: @article{fanSelfAssembledPlasmonicNanoparticle2010,
     title = {Self-{{Assembled Plasmonic Nanoparticle Clusters}}},
     author = {Fan, Jonathan A. and Wu, Chihhui and Bao, Kui and Bao, Jiming and Bardhan, Rizia and Halas, Naomi J. and Manoharan, Vinothan N. and Nordlander, Peter and Shvets, Gennady and Capasso, Federico},
     date = {2010-05-28},
     journaltitle = {Science},
     volume = {328},
     number = {5982},
     eprint = {20508125},
     eprinttype = {pmid},
     pages = {1135--1138},
     issn = {0036-8075, 1095-9203},
     doi = {10/cdpt9m},
     url = {https://science.sciencemag.org/content/328/5982/1135},
     urldate = {2019-10-01}
   }
   

10. Femtosecond Spatiotemporal Control with Multiple Knobs. D. Goswami, in CLEO/QELS: 2010 Laser Science to Photonic Applications (2010), pp. 1–2 [Abstract] [BibTeX]

    Abstract: For controlling non-resonant molecular fragmentation process, simultaneous effect of chirp and polarization of a femtosecond pulse is mutually independent. For multiphoton fluorescence microscopy and optical tweezers with high-repetition-rate lasers, inter-pulse separation and polarization is important.

     BibTeX: @inproceedings{goswamiFemtosecondSpatiotemporalControl2010,
      title = {Femtosecond Spatiotemporal Control with Multiple Knobs},
      booktitle = {{{CLEO}}/{{QELS}}: 2010 {{Laser Science}} to {{Photonic Applications}}},
      author = {Goswami, D.},
      date = {2010-05},
      pages = {1--2},
      doi = {10/gf6c82},
      eventtitle = {{{CLEO}}/{{QELS}}: 2010 {{Laser Science}} to {{Photonic Applications}}}
    }
    

11. Hot Chemistry with Cold Molecules. T. Goswami and D. Goswami, in Laser Pulse Phenomena and Applications (BoD – Books on Demand, 2010), pp. 371–388 [Abstract] [BibTeX]

    Abstract: Pulsed lasers are available in the gas, liquid, and the solid state. These lasers are also enormously versatile in their output characteristics yielding emission from very large energy pulses to very high peak-power pulses. Pulsed lasers are equally versatile in their spectral characteristics. This volume includes an impressive array of current research on pulsed laser phenomena and applications. Laser Pulse Phenomena and Applications covers a wide range of topics from laser powered orbital launchers, and laser rocket engines, to laser-matter interactions, detector and sensor laser technology, laser ablation, and biological applications.

     BibTeX: @incollection{goswamiHotChemistryCold2010,
      title = {Hot {{Chemistry}} with {{Cold Molecules}}},
      booktitle = {Laser {{Pulse Phenomena}} and {{Applications}}},
      author = {Goswami, Tapas and Goswami, Debabrata},
      date = {2010-12-30},
      eprint = {5XSfDwAAQBAJ},
      eprinttype = {googlebooks},
      pages = {371--388},
      publisher = {{BoD – Books on Demand}},
      isbn = {978-953-307-405-4}
    }
    

12. Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy. D. Goswami and A. Kumar De, Biophysical Journal 98(3), 586a (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Confocal microscopy, one of the modern day fluorescence laser-scanning microscopic techniques, is suffered from having sufficient out-of-focus signal. On the other hand, in multiphoton microscopy ultrafast laser pulses are commonly used to circumvent low multiphoton absorption cross-sections of common fluorophores; due to broad overlapping two-photon absorption (TPA) spectra of fluorophores and large spectral bandwidth of a short pulse, simultaneous excitation of many fluorophores is common demanding selective excitation of individual fluorophores if required. Addressing the first issue, our recent work has shown that ultrafast one-photon pulsed illumination leads to increased signal-to-noise ratio by controlling the fluorophore photo-physics.1-2 Considering TPA, we have demonstrated that photo-thermal corruption due to pulse pile-up effect is largely solvent-mediated and a rather slow process which can be taken care of by simple intensity modulation of a pulse-train.3-4 We have recently shown how precise delay between pair of ultrafast pulses can lead to possible selective excitation in microscopy.5 We have also demonstrated how gigantic peak-power of a femto-second laser pulse (with rather low average power) leads to stable optical trapping of latex nano-particles which is otherwise impossible with continuous-wave excitation (at the same average power).6

     BibTeX: @article{goswamiSpatioTemporalControlMultiphoton2010,
      title = {Spatio-{{Temporal Control}} in {{Multiphoton Fluorescence Laser-Scanning Microscopy}}},
      author = {Goswami, Debabrata and Kumar De, Arijit},
      date = {2010-01},
      journaltitle = {Biophysical Journal},
      shortjournal = {Biophysical Journal},
      volume = {98},
      number = {3},
      pages = {586a},
      issn = {00063495},
      doi = {10/cwqtj2},
      url = {https://linkinghub.elsevier.com/retrieve/pii/S000634950904990X},
      urldate = {2019-08-14}
    }
    

13. Towards Using Molecular Ions as Qubits: Femtosecond Control of Molecular Fragmentation with Multiple Knobs. T. Goswami, D. K. Das, and D. Goswami, Pramana 75(6), 1065–1069 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Non-resonant molecular fragmentation of n-propyl benzene with femtosecond laser pulses is dependent on the phase and polarization characteristics of the laser. We find that the effect of the chirp and polarization of the femtosecond pulse when applied simultaneously is mutually independent of each other, which makes chirp and polarization as useful ‘logic’ implementing knobs.

     BibTeX: @article{goswamiUsingMolecularIons2010,
      title = {Towards Using Molecular Ions as Qubits: {{Femtosecond}} Control of Molecular Fragmentation with Multiple Knobs},
      shorttitle = {Towards Using Molecular Ions as Qubits},
      author = {Goswami, Tapas and Das, Dipak K. and Goswami, Debabrata},
      date = {2010-12-01},
      journaltitle = {Pramana},
      shortjournal = {Pramana - J Phys},
      volume = {75},
      number = {6},
      pages = {1065--1069},
      issn = {0973-7111},
      doi = {10/cf945s},
      url = {https://doi.org/10.1007/s12043-010-0190-9},
      urldate = {2019-08-14}
    }
    

14. Two-Photon Quantum Dot Excitation during Optical Trapping. L. Jauffred and L. B. Oddershede, Nano Letters 10(5), 1927–1930 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: A single CW infrared laser beam can simultaneously trap and excite an individual colloidal quantum dot. Though the laser light is relatively weak, the excitation occurs through two-photon absorption. This finding eliminates the demand for an excitation light source in addition to a trapping laser in nanoscale experiments with simultaneous force-manipulation and quantum dot visualization. Also, we demonstrate that optical trapping efficiencies of individual quantum dots do not correlate with their emission wavelength or physical size.

     BibTeX: @article{jauffredTwoPhotonQuantumDot2010,
      title = {Two-{{Photon Quantum Dot Excitation}} during {{Optical Trapping}}},
      author = {Jauffred, Liselotte and Oddershede, Lene B.},
      date = {2010-05-12},
      journaltitle = {Nano Letters},
      shortjournal = {Nano Lett.},
      volume = {10},
      number = {5},
      pages = {1927--1930},
      issn = {1530-6984},
      doi = {10/b49kwx},
      url = {https://doi.org/10.1021/nl100924z},
      urldate = {2019-10-01}
    }
    

15. Applying Genetic Algorithm Optimization to a Folded Geometry Acousto-Optic Modulated Spatial Pulse Shaper. A. Nag, P. A. Chaphekar, and D. Goswami, Review of Scientific Instruments 81(1), 013101 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: A folded geometry acousto-optic modulator spatial pulse shaper has been designed for shaping individual pulses from a high power amplified laser. The design preserves the capability of computer programmable amplitude and phase modulation of femtosecond laser pulses. An additional application of genetic algorithm optimization approach for compressing a stretched pulse is also demonstrated for such a pulse shaper. Spectrally and temporally resolved optical gating technique is used to characterize the shaped pulses.

     BibTeX: @article{nagApplyingGeneticAlgorithm2010,
      title = {Applying Genetic Algorithm Optimization to a Folded Geometry Acousto-Optic Modulated Spatial Pulse Shaper},
      author = {Nag, Amit and Chaphekar, Prasad A. and Goswami, Debabrata},
      date = {2010-01-01},
      journaltitle = {Review of Scientific Instruments},
      shortjournal = {Review of Scientific Instruments},
      volume = {81},
      number = {1},
      pages = {013101},
      issn = {0034-6748},
      doi = {10/ddkc77},
      url = {https://aip.scitation.org/doi/abs/10.1063/1.3276682},
      urldate = {2019-08-14}
    }
    

16. Polarization Induced Control of Single and Two-Photon Fluorescence. A. Nag and D. Goswami, The Journal of Chemical Physics 132(15), 154508 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Modulation of two-photon absorption, two-photon fluorescence (TPF), as well as single-photon fluorescence (SPF), is shown through incident laser polarization for different fluorescent dyes. TPF intensity increases as the polarization changes from circular to linear irrespective of the dye, though the intensity and wavelength dependent studies of two-photon polarization ratio for any particular dye (e.g., Rhodamine 6G) reveal the nature of their excited state. SPF intensity of IR125 and IR144 dyes increases as the polarization changes from linear to circular. Thus, polarization studies indicate that in case of TPF, there is a preference toward the linear component while in case of SPF, the preference is toward the circular component of the incident laser beam. I. INTRODUCTION

     BibTeX: @article{nagPolarizationInducedControl2010,
      title = {Polarization Induced Control of Single and Two-Photon Fluorescence},
      author = {Nag, Amit and Goswami, Debabrata},
      date = {2010-04-21},
      journaltitle = {The Journal of Chemical Physics},
      shortjournal = {J. Chem. Phys.},
      volume = {132},
      number = {15},
      pages = {154508},
      issn = {0021-9606},
      doi = {10/bdr2kh},
      url = {https://aip.scitation.org/doi/abs/10.1063/1.3386574},
      urldate = {2019-08-14}
    }
    

17. Coumarin Derived Chromophores in the Donor–Acceptor–Donor Format That Gives Fluorescence Enhancement and Large Two-Photon Activity in Presence of Specific Metal Ions. D. Ray, A. Nag, A. Jana, D. Goswami, and P. K. Bharadwaj, Inorganica Chimica Acta 363(12), 2824–2832 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Two coumarin derived dyes (compounds La and L) have been synthesized in high yields by Schiff base condensation. On probing with a femtosecond laser, none of these compounds show any two-photon activity in the wavelength range, 760–860nm. However, La in presence of Zn(II) and L in presence of Mg(II), exhibit large two-photon absorption as well as emission in the same wavelength range. Theoretical calculations at the B3LYP functional with 6-31G∗ and LanL2DZ mixed basis set under DFT formalism support experimental results.

     BibTeX: @article{rayCoumarinDerivedChromophores2010,
      title = {Coumarin Derived Chromophores in the Donor–Acceptor–Donor Format That Gives Fluorescence Enhancement and Large Two-Photon Activity in Presence of Specific Metal Ions},
      author = {Ray, Debdas and Nag, Amit and Jana, Atanu and Goswami, Debabrata and Bharadwaj, Parimal K.},
      date = {2010-10-15},
      journaltitle = {Inorganica Chimica Acta},
      shortjournal = {Inorganica Chimica Acta},
      series = {Special Volume: {{Dedicated}} to {{Professor Animesh Chakravorty}}},
      volume = {363},
      number = {12},
      pages = {2824--2832},
      issn = {0020-1693},
      doi = {10/c2k85x},
      url = {http://www.sciencedirect.com/science/article/pii/S0020169310002161},
      urldate = {2019-08-14}
    }
    

18. Precursor-Mediated Crystallization Process in Suspensions of Hard Spheres. T. Schilling, H. J. Schöpe, M. Oettel, G. Opletal, and I. Snook, Physical Review Letters 105(2), 025701 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: We report on a large scale computer simulation study of crystal nucleation in hard spheres. Through a combined analysis of real- and reciprocal-space data, a picture of a two-step crystallization process is supported: First, dense, amorphous clusters form which then act as precursors for the nucleation of well-ordered crystallites. This kind of crystallization process has been previously observed in systems that interact via potentials that have an attractive as well as a repulsive part, most prominently in protein solutions. In this context the effect has been attributed to the presence of metastable fluid-fluid demixing. Our simulations, however, show that a purely repulsive system (that has no metastable fluid-fluid coexistence) crystallizes via the same mechanism.

     BibTeX: @article{schillingPrecursorMediatedCrystallizationProcess2010,
      title = {Precursor-{{Mediated Crystallization Process}} in {{Suspensions}} of {{Hard Spheres}}},
      author = {Schilling, T. and Schöpe, H. J. and Oettel, M. and Opletal, G. and Snook, I.},
      date = {2010-07-08},
      journaltitle = {Physical Review Letters},
      shortjournal = {Phys. Rev. Lett.},
      volume = {105},
      number = {2},
      pages = {025701},
      doi = {10/drvm4d},
      url = {https://link.aps.org/doi/10.1103/PhysRevLett.105.025701},
      urldate = {2019-10-01}
    }
    

19. Spreading of Colloid Clusters in a Quasi-One-Dimensional Channel. X. Xu, B. Lin, B. Cui, A. R. Dinner, and S. A. Rice, The Journal of Chemical Physics 132(8), 084902 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: The effect of hydrodynamic interactions on the spreading of clusters of colloid particles in a quasi-one-dimensional channel is analyzed both experimentally and theoretically. An nn$n$-particle cluster spreading diffusion coefficient is defined, in terms of the displacement Δx(t)Δx(t)$\Delta x\left(t\right)$ in time tt$t$, by Dn≡⟨[∑ni=1Δxi(t)]2⟩/2ntDn≡⟨[∑ni=1Δxi(t)]2⟩/2nt$D_n\equiv ⟨{\left[{\sum }_{i=1}^n\Delta x_i\left(t\right)\right]}^2⟩/2nt$, where the average is taken over all groups of nn$n$ adjacent particles. Our study focuses on the nn$n$-dependence of DnDn$D_n$ with some attention to the dependence of DnDn$D_n$ on colloid packing fraction. We find that the ratio of DnDn$D_n$ to the infinite dilution self-diffusion coefficient D0SD0S$D_S^0$ increases as nn$n$ increases, eventually saturating for large nn$n$. The observed dependence of DnDn$D_n$ on nn$n$ is in satisfactory agreement with the predictions obtained from both Stokesian dynamics simulations and hydrodynamic calculations using the method of reflections.

     BibTeX: @article{xuSpreadingColloidClusters2010,
      title = {Spreading of Colloid Clusters in a Quasi-One-Dimensional Channel},
      author = {Xu, Xinliang and Lin, Binhua and Cui, Bianxiao and Dinner, Aaron R. and Rice, Stuart A.},
      date = {2010-02-25},
      journaltitle = {The Journal of Chemical Physics},
      shortjournal = {J. Chem. Phys.},
      volume = {132},
      number = {8},
      pages = {084902},
      issn = {0021-9606},
      doi = {10.1063/1.3330414},
      url = {https://aip.scitation.org/doi/full/10.1063/1.3330414},
      urldate = {2019-10-01}
    }
    

20. Colloidal Self-Assembly Meets Nanofabrication: From Two-Dimensional Colloidal Crystals to Nanostructure Arrays. J. Zhang, Y. Li, X. Zhang, and B. Yang, Advanced Materials 22(38), 4249–4269 (2010) [Abstract] [PDF] [BibTeX]

    Abstract: Self-assembly of colloidal microspheres or nanospheres is an effective strategy for fabrication of ordered nanostructures. By combination of colloidal self-assembly with nanofabrication techniques, two-dimensional (2D) colloidal crystals have been employed as masks or templates for evaporation, deposition, etching, and imprinting, etc. These methods are defined as “colloidal lithography”, which is now recognized as a facile, inexpensive, and repeatable nanofabrication technique. This paper presents an overview of 2D colloidal crystals and nanostructure arrays fabricated by colloidal lithography. First, different methods for fabricating self-assembled 2D colloidal crystals and complex 2D colloidal crystal structures are summarized. After that, according to the nanofabrication strategy employed in colloidal lithography, related works are reviewed as colloidal-crystal-assisted evaporation, deposition, etching, imprinting, and dewetting, respectively.

     BibTeX: @article{zhangColloidalSelfAssemblyMeets2010,
      title = {Colloidal {{Self-Assembly Meets Nanofabrication}}: {{From Two-Dimensional Colloidal Crystals}} to {{Nanostructure Arrays}}},
      shorttitle = {Colloidal {{Self-Assembly Meets Nanofabrication}}},
      author = {Zhang, Junhu and Li, Yunfeng and Zhang, Xuemin and Yang, Bai},
      date = {2010},
      journaltitle = {Advanced Materials},
      volume = {22},
      number = {38},
      pages = {4249--4269},
      issn = {1521-4095},
      doi = {10/bwn4hf},
      url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201000755},
      urldate = {2019-10-01}
    }
    

2009

1. Molecular Structure-Property Correlations from Optical Nonlinearity and Thermal-Relaxation Dynamics. I. Bhattacharyya, S. Priyadarshi, and D. Goswami, Chemical Physics Letters 469(1), 104–109 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We apply ultrafast single beam Z-scan technique to measure saturation absorption coefficients and nonlinear-refraction coefficients of primary alcohols at 1560nm. The nonlinear effects result from vibronic transitions and cubic nonlinear-refraction. To measure the pure total third-order nonlinear susceptibility, we removed thermal effects with a frequency optimized optical-chopper. Our measurements of thermal-relaxation dynamics of alcohols, from 1560nm thermal lens pump and 780nm probe experiments revealed faster and slower thermal-relaxation timescales, respectively, from conduction and convection. The faster timescale accurately predicts thermal-diffusivity, which decreases linearly with alcohol chain-lengths since thermal-relaxation is slower in heavier molecules. The relation between thermal-diffusivity and alcohol chain-length confirms structure-property relationship.

    BibTeX: @article{bhattacharyyaMolecularStructurepropertyCorrelations2009,
     title = {Molecular Structure-Property Correlations from Optical Nonlinearity and Thermal-Relaxation Dynamics},
     author = {Bhattacharyya, Indrajit and Priyadarshi, Shekhar and Goswami, Debabrata},
     date = {2009-02-03},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {469},
     number = {1},
     pages = {104--109},
     issn = {0009-2614},
     doi = {10/cpq233},
     url = {http://www.sciencedirect.com/science/article/pii/S0009261408017028},
     urldate = {2019-08-14}
   }
   

2. Adding New Dimensions to Laser-Scanning Fluorescence Microscopy. A. K. De and D. Goswami, Journal of Microscopy 233(2), 320–325 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We describe a novel method of optical imaging by exploiting simple ideas borrowed from pulsed optics. We show that the use of ultrafast pulsed one-photon excitation in laser-scanning fluorescence microscopy dramatically brings together several advantages offered by two widely used present day microscopic techniques, confocal and multi-photon fluorescence microscopy. The method appears as a novel tool in the context of laser-scanning fluorescence microscopy by having a ‘built-in’ 3D spatial resolution.

    BibTeX: @article{deAddingNewDimensions2009,
     title = {Adding New Dimensions to Laser-Scanning Fluorescence Microscopy},
     author = {De, A. K. and Goswami, D.},
     date = {2009},
     journaltitle = {Journal of Microscopy},
     volume = {233},
     number = {2},
     pages = {320--325},
     issn = {1365-2818},
     doi = {10/fd3jh9},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03122.x},
     urldate = {2019-08-14}
   }
   

3. Coherent Control in Multiphoton Fluorescence Imaging. A. K. De and D. Goswami, in Multiphoton Microscopy in the Biomedical Sciences IX (International Society for Optics and Photonics, 2009), 7183, p. 71832B [Abstract] [PDF] [BibTeX]

   Abstract: In multiphoton fluorescence laser-scanning microscopy ultrafast laser pulses, i.e. light pulses having pulse-width ≤ 1picosecond (1 ps = 10^-12 s), are commonly used to circumvent the low multiphoton absorption cross-sections of common fluorophores. Starting with a discussion on how amplitude modulation of ultrashort pulse-train enhances the two-photon fluorescence providing deep insight into laser-induced photo-thermal damage, the effect of controlling time lag between phase-locked laser pulses on imaging is described. In addition, the prospects of laser pulse-shaping in signal enhancement (by temporal pulse-compression at the sample) and selective excitation of fluorophores (by manipulating the phase and/or amplitude of different frequency components within the pulse) are discussed with promising future applications lying ahead.

    BibTeX: @inproceedings{deCoherentControlMultiphoton2009,
     title = {Coherent Control in Multiphoton Fluorescence Imaging},
     booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-02-25},
     volume = {7183},
     pages = {71832B},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/d2cztk},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7183/71832B/Coherent-control-in-multiphoton-fluorescence-imaging/10.1117/12.807687.short},
     urldate = {2019-08-14},
     eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}}
   }
   

4. A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy. A. K. De and D. Goswami, Journal of Microscopy 235(2), 119–123 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We describe a very simple but elegant approach to two-photon fluorescence signal enhancement by intensity modulation with immediate application in two-photon laser-scanning fluorescence microscopy. This method of enhancement shows potential application in any microscopic technique that result from non-linear photon absorption and plays a pivotal role in live cell imaging.

    BibTeX: @article{deSimpleTwistSignal2009,
     title = {A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy},
     author = {De, A. K. and Goswami, D.},
     date = {2009},
     journaltitle = {Journal of Microscopy},
     volume = {235},
     number = {2},
     pages = {119--123},
     issn = {1365-2818},
     doi = {10/ckpt72},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03176.x},
     urldate = {2019-08-14}
   }
   

5. Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination. A. K. De, D. Roy, A. Dutta, and D. Goswami, Applied Optics 48(31), G33–G37 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: Here we report how ultrafast pulsed illumination at low average power results in a stable three-dimensional (3D) optical trap holding latex nanoparticles which is otherwise not possible with continuous wave lasers at the same power level. The gigantic peak power of a femtosecond pulse exerts a huge instantaneous gradient force that has been predicted theoretically earlier and implemented for microsecond pulses in a different context by others. In addition, the resulting two-photon fluorescence allows direct observation of trapping events by providing intrinsic 3D resolution.

    BibTeX: @article{deStableOpticalTrapping2009,
     title = {Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination},
     author = {De, Arijit Kumar and Roy, Debjit and Dutta, Aveek and Goswami, Debabrata},
     date = {2009-11-01},
     journaltitle = {Applied Optics},
     shortjournal = {Appl. Opt., AO},
     volume = {48},
     number = {31},
     pages = {G33-G37},
     issn = {2155-3165},
     doi = {10/b9sxj4},
     url = {https://www.osapublishing.org/ao/abstract.cfm?uri=ao-48-31-G33},
     urldate = {2019-08-14}
   }
   

6. A Systematic Study on Fluorescence Enhancement under Single-photon Pulsed Illumination. A. K. De and D. Goswami, Journal of Fluorescence 19(5), 931–937 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: We present a detailed study on fluorescence enhancement by ‘stroboscopic’ illumination with light pulses having duration ranging from few milliseconds to sub-picoseconds. We show how a delicate balance between pulse width and pulse repetition rate can result in an unprecedented fluorescence enhancement that has immediate applications in fluorescence imaging.

    BibTeX: @article{deSystematicStudyFluorescence2009,
     title = {A {{Systematic Study}} on {{Fluorescence Enhancement}} under {{Single-photon Pulsed Illumination}}},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-09-01},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {19},
     number = {5},
     pages = {931--937},
     issn = {1573-4994},
     doi = {10/bk2648},
     url = {https://doi.org/10.1007/s10895-009-0489-4},
     urldate = {2019-08-14}
   }
   

7. Three-Dimensional Image Formation under Single-Photon Ultra-Short Pulsed Illumination. A. K. De and D. Goswami, in Scanning Microscopy 2009 (International Society for Optics and Photonics, 2009), 7378, p. 737827 [Abstract] [PDF] [BibTeX]

   Abstract: The major thrust of modern day fluorescence laser-scanning microscopy have been towards achieving better and better depth resolution embodied by the invention and subsequent development of confocal and multi-photon microscopic techniques. However, each method bears its own limitations: in having sufficient background fluorescence and photodamage resulting from out-of-focus illumination for the former, while low multi-photon absorption cross-sections of common fluorophores for the latter. Here we show how the intelligent choice of single-photon ultrashort pulsed illumination can circumvent all these shortcomings by exemplifying the tiny spatial stretch of an ultrashort pulse. Besides achieving a novel way of optical sectioning, this new method offers improved signal-to-noise ratio as well as reduced photo-damage which are crucial for live cell imaging under prolonged exposure to light.

    BibTeX: @inproceedings{deThreedimensionalImageFormation2009,
     title = {Three-Dimensional Image Formation under Single-Photon Ultra-Short Pulsed Illumination},
     booktitle = {Scanning {{Microscopy}} 2009},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-05-22},
     volume = {7378},
     pages = {737827},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/b7mtnv},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7378/737827/Three-dimensional-image-formation-under-single-photon-ultra-short-pulsed/10.1117/12.822773.short},
     urldate = {2019-08-14},
     eventtitle = {Scanning {{Microscopy}} 2009}
   }
   

8. Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De and D. Goswami, Journal of Biomedical Optics 14(6), 064018 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: In multiphoton fluorescence laser-scanning microscopy, ultrafast laser pulses [i.e., light pulses having pulse width 1 ps (1 ps=10−12 s)] are commonly employed to circumvent the low-multiphoton absorption cross-sections of common fluorophores. Because of the broad overlapping two-photon absorption spectra of fluorophores and the large spectral bandwidth of a short pulse, simultaneous excitation of many fluorophores is common, which justifies a persistent demand for selective excitation of individual fluorophores. We describe the use of pulse-pair excitation with possibilities of controlling molecular fluorescence in laser-scanning microscopy and compare it with coherent control using pulse sequence [De and Goswami, "Coherent control in multiphoton fluorescence imaging," Proc. SPIE 7183, 71832B (2009)].

    BibTeX: @article{deUltrafastPulsepairControl2009,
     title = {Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2009-11},
     journaltitle = {Journal of Biomedical Optics},
     shortjournal = {JBO},
     volume = {14},
     number = {6},
     pages = {064018},
     issn = {1083-3668, 1560-2281},
     doi = {10/fvc8h7},
     url = {https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-14/issue-6/064018/Ultrafast-pulse-pair-control-in-multiphoton-fluorescence-laser-scanning-microscopy/10.1117/1.3268440.short},
     urldate = {2019-08-14}
   }
   

9. Local Viscosity of Binary Water+Glycerol Mixtures at Liquid/Liquid Interfaces Probed by Time-Resolved Surface Second Harmonic Generation. P. Fita, A. Punzi, and E. Vauthey, The Journal of Physical Chemistry C 113(48), 20705–20712 (2009) [Abstract] [PDF] [BibTeX]

   Abstract: The excited-state relaxation of malachite green and brilliant green in solvents of various viscosity has been investigated at liquid/liquid interfaces and in bulk solutions by surface second harmonic generation and transient absorption spectroscopy. Mixtures of water and glycerol in various proportions have been used as solvents of variable viscosity. Transient absorption measurements in bulk revealed that both dyes are suitable as a probe of local viscosity for water+glycerol mixtures and that two of three processes following the optical excitation exhibit the same power dependence on solvent viscosity. This observation leads to assignment of the processes to a twist and twist-back of the aromatic rings attached to the central carbon atom of the dye. Therefore, identification of the intermediate state observed in the radiationless deactivation pathway with the twisted form of the dye has been supported. The time profiles of the second harmonic signal recorded at water+glycerol/dodecane interfaces have been found to be monoexponential at low dye concentrations (below 10−5 M) and biexponential at higher concentrations, and therefore the origin of the slower component has been attributed to the relaxation of dye aggregates adsorbed at the interface. The decay times measured at interfaces increased with increasing amount of glycerol in the mixture, but the rise was slower than in bulk solution. Therefore, the viscosity at the interfacial region, higher than that of the bulk solution, is mainly determined by structural modification of the solvent resulting from interactions between the two liquids that constitute the interface and addition of glycerol affects viscosity, only to a lesser extent. We have also shown that if the viscosity of the upper layer is much higher (at least 1 order of magnitude) than that of water or short alkanes, a slow-down of the relaxation is observed. This contradicts earlier findings and means that large amplitude motion of all three rings is involved in the deactivation of the excited molecule, but the rotation of the phenyl ring, which is smaller than the alkyl-substituted aniline groups, becomes a bottleneck for the relaxation in very viscous environments.

    BibTeX: @article{fitaLocalViscosityBinary2009,
     title = {Local {{Viscosity}} of {{Binary Water}}+{{Glycerol Mixtures}} at {{Liquid}}/{{Liquid Interfaces Probed}} by {{Time-Resolved Surface Second Harmonic Generation}}},
     author = {Fita, Piotr and Punzi, Angela and Vauthey, Eric},
     date = {2009-12-03},
     journaltitle = {The Journal of Physical Chemistry C},
     shortjournal = {J. Phys. Chem. C},
     volume = {113},
     number = {48},
     pages = {20705--20712},
     issn = {1932-7447},
     doi = {10/fjkvrb},
     url = {https://doi.org/10.1021/jp906676x},
     urldate = {2019-10-01}
   }
   

10. Control of Laser Induced Molecular Fragmentation of N-Propyl Benzene Using Chirped Femtosecond Laser Pulses. T. Goswami, S. K. Karthick Kumar, A. Dutta, and D. Goswami, Chemical Physics 360(1), 47–52 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: We present the effect of chirping a femtosecond laser pulse on the fragmentation of n-propyl benzene. An enhancement of an order of magnitude for the relative yields of C3H3+ and C5H5+ in the case of negatively chirped pulses and C6H5+ in the case of positively chirped pulses with respect to the transform-limited pulse indicates that in some fragmentation channel, coherence of the laser field plays an important role. For the relative yield of all other heavier fragment ions, resulting from the interaction of the intense laser field with the molecule, there is no such enhancement effect with the sign of chirp, within experimental errors. The importance of the laser phase is further reinforced through a direct comparison of the fragmentation results with the second harmonic of the chirped laser pulse with identical bandwidth.

     BibTeX: @article{goswamiControlLaserInduced2009,
      title = {Control of Laser Induced Molecular Fragmentation of N-Propyl Benzene Using Chirped Femtosecond Laser Pulses},
      author = {Goswami, Tapas and Karthick Kumar, S. K. and Dutta, Aveek and Goswami, Debabrata},
      date = {2009-06-12},
      journaltitle = {Chemical Physics},
      shortjournal = {Chemical Physics},
      volume = {360},
      number = {1},
      pages = {47--52},
      issn = {0301-0104},
      doi = {10/b2h79c},
      url = {http://www.sciencedirect.com/science/article/pii/S0301010409001219},
      urldate = {2019-08-14}
    }
    

11. Femtosecond Spatio-Temporal Control. D. Goswami, T. Goswami, A. K. De, D. Roy, D. Das, and S. K. K. Kumar, International Conference on Optics and Photonics 4 (2009) [Abstract] [BibTeX]

    Abstract: We explore the simultaneous control of centre of mass and internal degrees of freedom of molecules. We have found that the fragmentation pattern of n-propyl benzene molecule is coherently affected by a femtosecond pulse with linear frequency modulation. The fragments (C3H3+, C5H5+) are enhanced with negatively chirped pulses while the C6H5+ fragment is reduced with positively chirped pulses. Similarly, using both continuous-wave (CW) and high repetition-rate femtosecond lasers, we present stable 3-dimensional trapping of 1μm polystyrene microspheres. We also stably trapped 100nm latex nanoparticles using the femtosecond mode-locked laser at a very low average power where the CW lasers cannot trap, demonstrating the significance of the high peak power of the fleeting temporal existence of the femtosecond pulses. Trapping was visualized through dark-field microscopy as well as through a noise free detection using two-photon fluorescence as a diagnostics tool due to its intrinsic 3-dimensional resolution. Simultaneous control of centre of mass and internal degrees of freedom of molecules would require coupling of various control parameters where we demonstrate that coupling of control parameters cannot be an apriority predictable determinant function.

     BibTeX: @article{goswamiFemtosecondSpatioTemporalControl2009,
      title = {Femtosecond {{Spatio-Temporal Control}}},
      author = {Goswami, Debabrata and Goswami, T and De, A K and Roy, D and Das, D and Kumar, S K Karthick},
      date = {2009},
      journaltitle = {International Conference on Optics and Photonics},
      pages = {4}
    }
    

12. Probing the Ultrafast Solution Dynamics of a Cyanine Dye in an Organic Solvent Interfaced with Water. T. Goswami, S. K. K. Kumar, A. Dutta, and D. Goswami, The Journal of Physical Chemistry B 113(51), 16332–16336 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Dependence of ultrafast dynamics on the excited state evolution and ground state recovery of a cyanine dye (IR125) in dichloromethane (DCM) solvent interfaced with neat water is presented. We use degenerate pump−probe transient absorption spectroscopy to show that the excited-state dynamics of the dye molecule is strongly dependent on the position of the measurements from bulk DCM solution to the solution near the water layer. The decay component of the transient corresponding to the excited state lifetime increases from bulk DCM solution to its interface with water. Such results show that the effect of the presence of water layer over the dye solution in DCM extends several micrometers, indicating the surfactant nature of the IR125 molecules, and provides us a measure of the penetration of water into the DCM layer. The initial ultrafast decay component (coherent spike) directly correlates to the pulse-width of our near-transform limited pulses used in these experiments. This approach of measuring the excited state decay of a dye across an immiscible liquid interface can provide important characteristics of microtransport across such interfaces.

     BibTeX: @article{goswamiProbingUltrafastSolution2009,
      title = {Probing the {{Ultrafast Solution Dynamics}} of a {{Cyanine Dye}} in an {{Organic Solvent Interfaced}} with {{Water}}},
      author = {Goswami, Tapas and Kumar, S. K. Karthick and Dutta, Aveek and Goswami, Debabrata},
      date = {2009-12-24},
      journaltitle = {The Journal of Physical Chemistry B},
      shortjournal = {J. Phys. Chem. B},
      volume = {113},
      number = {51},
      pages = {16332--16336},
      issn = {1520-6106},
      doi = {10/dc3b67},
      url = {https://doi.org/10.1021/jp903753u},
      urldate = {2019-08-14}
    }
    

13. Spectrally Resolved Photon Echo Spectroscopy of Zn(II), Co(II) and Ni(II)–Octaethyl Porphyrins. S. K. Karthick Kumar, V. Tiwari, T. Goswami, and D. Goswami, Chemical Physics Letters 476(1), 31–36 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Spectrally resolved femtosecond three-pulse photon echo signal from some metal–octaethyl porphyrins (OEPs) like Zn(II)–OEP, Ni(II)–OEP, Co(II)–OEP is reported. Excited state dynamics is studied by time evolving photon echo spectra for different values of coherence and population relaxation times. Dependence on the spectrally resolved photon echo spectra on varying metal center is analyzed. For all these metallo-porphyrins, the electronic relaxation timescale is found to be limited by our laser pulsewidth of 50fs whereas the timescale for intramolecular vibrational relaxation, occurring within the Q00 band was found to be over a picosecond for Co(II)–OEP and Ni(II)–OEP and within a picosecond for Zn(II)–OEP.

     BibTeX: @article{karthickkumarSpectrallyResolvedPhoton2009,
      title = {Spectrally Resolved Photon Echo Spectroscopy of {{Zn}}({{II}}), {{Co}}({{II}}) and {{Ni}}({{II}})–Octaethyl Porphyrins},
      author = {Karthick Kumar, S. K. and Tiwari, Vivek and Goswami, Tapas and Goswami, Debabrata},
      date = {2009-07-07},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {476},
      number = {1},
      pages = {31--36},
      issn = {0009-2614},
      doi = {10/fpmh7d},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409006666},
      urldate = {2019-08-14}
    }
    

14. Visible 20-Femtosecond Pulse Generation by Double-Pass Non-Collinear Optical Parametric Amplifier. S. K. K. Kumar, T. Goswami, I. Bhattacharyya, and D. Goswami, Current Science 96(11), 1496–1500 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: We report a new design and construction of a highpower, white light seeded double-pass non-collinear optical parametric amplifier (NOPA) in the visible wavelength using a single amplifier crystal. For its successful implementation, many important practical considerations are discussed in detail. Tunable femtosecond pulses were obtained with pulse widths less than 20 fs and characterized using frequency-resolved optical gating technique. The generated visible pulse, tunable from 490 to 740 nm from the NOPA, was further optimized by second harmonic and four-wave mixing signals.

     BibTeX: @article{kumarVisible20femtosecondPulse2009,
      title = {Visible 20-Femtosecond Pulse Generation by Double-Pass Non-Collinear Optical Parametric Amplifier},
      author = {Kumar, S. K. Karthick and Goswami, T. and Bhattacharyya, I. and Goswami, D.},
      date = {2009},
      journaltitle = {Current Science},
      volume = {96},
      number = {11},
      eprint = {24104778},
      eprinttype = {jstor},
      pages = {1496--1500},
      issn = {0011-3891},
      url = {https://www.jstor.org/stable/24104778},
      urldate = {2019-08-14}
    }
    

15. Towards Self-Replicating Materials of DNA-functionalized Colloids. M. E. Leunissen, R. Dreyfus, R. Sha, T. Wang, N. C. Seeman, D. J. Pine, and P. M. Chaikin, Soft Matter 5(12), 2422–2430 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: We report the first results of ongoing research that involves the creation of a new class of non-biological materials designed to self-replicate and, as a result, to grow exponentially. We propose a system design that exploits the strong specificity and thermal reversibility of the interactions between colloidal particles functionalized with complementary single-stranded DNA ‘sticky ends’. Here, we experimentally test the fundamentals of the different steps that constitute the self-replication scheme. First of all, we quantitatively study the equilibrium and kinetic aspects of the aggregation–dissociation behavior of the particles. We find that the dissociation transition is very sharp (∼1 °C) and that it occurs at unexpectedly low temperatures, with the dissociation temperature shifting further down when the fraction of sticky ends becomes smaller. The sharpness of the transition and its sensitivity to the sticky end fraction are important control parameters in our self-replication scheme. We further find that for our present purposes it is best to use a DNA construct with a double-stranded backbone, as this largely prevents unwanted hybridization events, such as secondary structure formation. The latter is seen to lead to peculiar aggregation kinetics, due to a competition between inter- and intra-particle hybridization. Finally, we show how one can obtain dual recognition at different temperatures by functionalizing a single particle species with two distinct DNA sequences and we demonstrate the formation of permanent bonds, using the chemical intercalator psoralen and long-wavelength UV exposure.

     BibTeX: @article{leunissenSelfreplicatingMaterialsDNAfunctionalized2009,
      title = {Towards Self-Replicating Materials of {{DNA-functionalized}} Colloids},
      author = {Leunissen, Mirjam E. and Dreyfus, Rémi and Sha, Roujie and Wang, Tong and Seeman, Nadrian C. and Pine, David J. and Chaikin, Paul M.},
      date = {2009-06-09},
      journaltitle = {Soft Matter},
      shortjournal = {Soft Matter},
      volume = {5},
      number = {12},
      pages = {2422--2430},
      issn = {1744-6848},
      doi = {10/cj2sn9},
      url = {https://pubs.rsc.org/en/content/articlelanding/2009/sm/b817679e},
      urldate = {2019-10-01}
    }
    

16. Protein Aggregation Kinetics, Mechanism, and Curve-Fitting: A Review of the Literature. A. M. Morris, M. A. Watzky, and R. G. Finke, Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics 1794(3), 375–397 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Protein aggregation is an important phenomenon that alternatively is part of the normal functioning of nature or, central to this review, has negative consequences via its hypothesized central role in neurodegenerative diseases. A key to controlling protein aggregation is understanding the mechanism(s) of protein aggregation. Kinetic studies, data curve-fitting, and analysis are, in turn, keys to rigorous mechanistic studies. The main goal of this review is to analyze and report on the primary literature contributions to protein aggregation kinetics, mechanism, and curve-fitting. Following a brief introduction, the multiple different physical methods that have been employed to follow protein aggregation are presented and briefly discussed. Next, key information on the starting proteins and especially the products, and any detectable intermediates, involved in protein aggregation are presented. This is followed by tabulation (in the Supporting information) and discussion (in the main text), of the many approaches in the literature striving to determine the kinetics and mechanism of protein aggregation. It is found that these approaches can be broadly divided into three categories: (i) kinetic and thermodynamic, (ii) empirical, and (iii) other approaches. The first two approaches are the main focus of the present contribution, their goal being curve-fitting the available kinetic data and obtaining quantitative rate constants characterizing the nucleation, growth, and any other parts of the overall aggregation process. The large literature of protein aggregation is distilled down to five classes of postulated mechanisms: i) the subsequent monomer addition mechanism, ii) the reversible association mechanism, iii) prion aggregation mechanisms, iv) an “Ockham’s razor”/minimalistic model first presented in 1997 and known as the Finke–Watzky 2-step model, and v) quantitative structure activity relationship models. These five classes of mechanisms are reviewed in detail in historical order; where possible corresponding kinetic equations, and fits to aggregation data via the proposed mechanisms, are analyzed and discussed. The five classes of mechanisms are then analyzed and discussed in terms of their similarities and differences to one another. Also included is a brief discussion of selected empirical approaches used to investigate protein aggregation. Three problem areas in the protein aggregation kinetic and mechanistic studies area are identified, and a Summary and Conclusions section is provided en route to moving the field forward towards the still unachieved goal of unequivocal elucidation of the mechanism(s) of protein aggregation.

     BibTeX: @article{morrisProteinAggregationKinetics2009,
      title = {Protein Aggregation Kinetics, Mechanism, and Curve-Fitting: {{A}} Review of the Literature},
      shorttitle = {Protein Aggregation Kinetics, Mechanism, and Curve-Fitting},
      author = {Morris, Aimee M. and Watzky, Murielle A. and Finke, Richard G.},
      date = {2009-03-01},
      journaltitle = {Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics},
      shortjournal = {Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics},
      volume = {1794},
      number = {3},
      pages = {375--397},
      issn = {1570-9639},
      doi = {10/djk6mq},
      url = {http://www.sciencedirect.com/science/article/pii/S1570963908003488},
      urldate = {2019-10-01}
    }
    

17. Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes. A. Nag and D. Goswami, Journal of Photochemistry and Photobiology A: Chemistry 206(2), 188–197 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: For a series of rhodamine dyes, two-photon absorption (TPA) and two-photon fluorescence (TPF) have been performed in different solvents. Solvent-dependent TPA spectra of these dyes were measured with open aperture z-scan method and compared to their respective single-photon spectra at equivalent energies. In the TPA spectra, relative peak intensities and positions are highly solvent dependent, which could be a result of vibronic couplings that depend on solvent environment. Measured TPA cross-sections of rhodamine dyes are consistently higher in nonpolar solvents. Certain complementary and similarity between TPA and TPF are also elucidated. Finally, a two-photon figure-of-merit is presented for these dyes in different solvents as a function of wavelength.

     BibTeX: @article{nagSolventEffectTwophoton2009,
      title = {Solvent Effect on Two-Photon Absorption and Fluorescence of Rhodamine Dyes},
      author = {Nag, Amit and Goswami, Debabrata},
      date = {2009-08-15},
      journaltitle = {Journal of Photochemistry and Photobiology A: Chemistry},
      shortjournal = {Journal of Photochemistry and Photobiology A: Chemistry},
      volume = {206},
      number = {2},
      pages = {188--197},
      issn = {1010-6030},
      doi = {10/c4zdx8},
      url = {http://www.sciencedirect.com/science/article/pii/S1010603009002676},
      urldate = {2019-08-14}
    }
    

18. Two-Photon Cross-Section Measurements Using an Optical Chopper: Z-Scan and Two-Photon Fluorescence Schemes. A. Nag, A. K. De, and D. Goswami, Journal of Physics B: Atomic, Molecular and Optical Physics 42(6), 065103 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: An effective z-scan setup with a minimum thermal effect is shown for intensity-dependent measure of two-photon absorption (TPA) with high-repetition rate lasers. Use of an additional intensity modulation with an optical chopper provides enough blanking time for a high-repetition rate laser to yield equally accurate results in TPA measurements compared to a low repetition laser. Extension of this method of thermal effect management with an optical chopper to emission studies also results in good correspondence for two-photon cross-section measurements from either z-scan or two-photon fluorescence techniques. The method also significantly enhances two-photon fluorescence, which could be promising for multiphoton microscopy.

     BibTeX: @article{nagTwophotonCrosssectionMeasurements2009,
      title = {Two-Photon Cross-Section Measurements Using an Optical Chopper: Z-Scan and Two-Photon Fluorescence Schemes},
      shorttitle = {Two-Photon Cross-Section Measurements Using an Optical Chopper},
      author = {Nag, Amit and De, Arijit Kumar and Goswami, Debabrata},
      date = {2009-03-28},
      journaltitle = {Journal of Physics B: Atomic, Molecular and Optical Physics},
      volume = {42},
      number = {6},
      pages = {065103},
      issn = {0953-4075, 1361-6455},
      doi = {10/bhffqb},
      url = {http://stacks.iop.org/0953-4075/42/i=6/a=065103?key=crossref.bf9dc5810ad233241ea2c717000e14f8},
      urldate = {2018-12-10}
    }
    

19. Nanofabrication by Self-Assembly. G. A. Ozin, K. Hou, B. V. Lotsch, L. Cademartiri, D. P. Puzzo, F. Scotognella, A. Ghadimi, and J. Thomson, Materials Today 12(5), 12–23 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: The self-assembly paradigm in chemistry, physics and biology has matured scientifically over the past two-decades to a point of sophistication that one can begin to exploit its numerous attributes in nanofabrication. In what follows we will take a brief look at current thinking about self-assembly and with some recent examples taken from our own work examine how nanofabrication has benefited from self-assembly.

     BibTeX: @article{ozinNanofabricationSelfassembly2009,
      title = {Nanofabrication by Self-Assembly},
      author = {Ozin, Geoffrey A. and Hou, Kun and Lotsch, Bettina V. and Cademartiri, Ludovico and Puzzo, Daniel P. and Scotognella, Francesco and Ghadimi, Arya and Thomson, Jordan},
      date = {2009-05-01},
      journaltitle = {Materials Today},
      shortjournal = {Materials Today},
      volume = {12},
      number = {5},
      pages = {12--23},
      issn = {1369-7021},
      doi = {10/c7mc9z},
      url = {http://www.sciencedirect.com/science/article/pii/S1369702109701567},
      urldate = {2019-10-01}
    }
    

20. Acyclic Donor–Acceptor–Donor Chromophores for Large Enhancement of Two-Photon Absorption Cross-Section in the Presence of Mg(II), Ca(II) or Zn(II) Ions. D. Ray, A. Nag, D. Goswami, and P. K. Bharadwaj, Journal of Luminescence 129(3), 256–262 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: Two new chromophores in the format, donor–acceptor–donor, have been synthesized in high yields from easily available starting materials. These compounds do not show any two-photon absorption (TPA) cross-section in the wavelength range, 780–900nm when probed by the Z-scan technique with a femtosecond laser. However, in presence of Zn(II), Ca(II) or Mg(II) ion, each compound gives exceptionally large TPA cross-section in the same wavelength range.

     BibTeX: @article{rayAcyclicDonorAcceptor2009,
      title = {Acyclic Donor–Acceptor–Donor Chromophores for Large Enhancement of Two-Photon Absorption Cross-Section in the Presence of {{Mg}}({{II}}), {{Ca}}({{II}}) or {{Zn}}({{II}}) Ions},
      author = {Ray, Debdas and Nag, Amit and Goswami, Debabrata and Bharadwaj, Parimal K.},
      date = {2009-03-01},
      journaltitle = {Journal of Luminescence},
      shortjournal = {Journal of Luminescence},
      volume = {129},
      number = {3},
      pages = {256--262},
      issn = {0022-2313},
      doi = {10.1016/j.jlumin.2008.10.005},
      url = {http://www.sciencedirect.com/science/article/pii/S0022231308002858},
      urldate = {2019-08-14}
    }
    

21. Fundamentals of Statistical and Thermal Physics. F. Reif, (Waveland Press, 2009) [Abstract] [BibTeX]

    Abstract: All macroscopic systems consist ultimately of atoms obeying the laws of quantum mechanics. That premise forms the basis for this comprehensive text, intended for a first upper-level course in statistical and thermal physics. Reif emphasizes that the combination of microscopic concepts with some statistical postulates leads readily to conclusions on a purely macroscopic level. The authors writing style and penchant for description energize interest in condensed matter physics as well as provide a conceptual grounding with information that is crystal clear and memorable.Reif first introduces basic probability concepts and statistical methods used throughout all of physics. Statistical ideas are then applied to systems of particles in equilibrium to enhance an understanding of the basic notions of statistical mechanics, from which derive the purely macroscopic general statements of thermodynamics. Next, he turns to the more complicated equilibrium situations, such as phase transformations and quantum gases, before discussing nonequilibrium situations in which he treats transport theory and dilute gases at varying levels of sophistication. In the last chapter, he addresses some general questions involving irreversible processes and fluctuations.A large amount of material is presented to facilitate students later access to more advanced works, to allow those with higher levels of curiosity to read beyond the minimum given on a topic, and to enhance understanding by presenting several ways of looking at a particular question. Formatting within the text either signals material that instructors can assign at their own discretion or highlights important results for easy reference to them. Additionally, by solving many of the 230 problems contained in the text, students activate and embed their knowledge of the subject matter.

     BibTeX: @book{reifFundamentalsStatisticalThermal2009,
      title = {Fundamentals of {{Statistical}} and {{Thermal Physics}}},
      author = {Reif, F.},
      date = {2009-01-05},
      eprint = {ObsbAAAAQBAJ},
      eprinttype = {googlebooks},
      publisher = {{Waveland Press}},
      isbn = {978-1-4786-1005-2},
      pagetotal = {672}
    }
    

22. Towards Spatio-Temporal Control in Optical Trapping. D. Roy, A. K. De, and D. Goswami, in Optical Trapping and Optical Micromanipulation VI (International Society for Optics and Photonics, 2009), 7400, p. 74000G [Abstract] [PDF] [BibTeX]

    Abstract: Using both continuous-wave (CW) and high repetition rate femtosecond lasers, we present stable 3-dimensional trapping of 1μm polystyrene microspheres. We also stably trapped 100nm latex nanoparticles using the femtosecond mode-locked laser at a very low average power where the CW lasers cannot trap, demonstrating the significance of the fleeting temporal existence of the femtosecond pulses. Trapping was visualized through dark-field microscopy as well as through a noise free detection using two-photon fluorescence as a diagnostics tool owing to its intrinsic 3- dimensional resolution. Comparison between a Gaussian versus a flat-top Gaussian beam profile demonstrates the importance of laser spatial mode in optical trapping.

     BibTeX: @inproceedings{roySpatiotemporalControlOptical2009,
      title = {Towards Spatio-Temporal Control in Optical Trapping},
      booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VI}}},
      author = {Roy, Debjit and De, Arijit Kumar and Goswami, Debabrata},
      date = {2009-08-20},
      volume = {7400},
      pages = {74000G},
      publisher = {{International Society for Optics and Photonics}},
      doi = {10/fpdhxs},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7400/74000G/Towards-spatio-temporal-control-in-optical-trapping/10.1117/12.824372.short},
      urldate = {2019-08-14},
      eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation VI}}}
    }
    

23. Mechanical Properties of a Giant Liposome Studied Using Optical Tweezers. Y. Shitamichi, M. Ichikawa, and Y. Kimura, Chemical Physics Letters 479(4), 274–278 (2009) [Abstract] [PDF] [BibTeX]

    Abstract: The mechanical properties of a micrometer-sized giant liposome are studied by deforming it from the inside using dual-beam optical tweezers. As the liposome is extended, its shape changes from a sphere to a lemon shape, and finally, a tubular part is generated. The surface tension σ and the bending rigidity κ of the lipid membrane are obtained from the measured force–extension curve. In a one-phase liposome, it was found that σ increases as the charged component increases but κ remains approximately constant. In a two-phase liposome, the characteristic deformation and the force–extension curve differ from those observed for the one-phase liposome.

     BibTeX: @article{shitamichiMechanicalPropertiesGiant2009,
      title = {Mechanical Properties of a Giant Liposome Studied Using Optical Tweezers},
      author = {Shitamichi, Yoko and Ichikawa, Masatoshi and Kimura, Yasuyuki},
      date = {2009-09-17},
      journaltitle = {Chemical Physics Letters},
      shortjournal = {Chemical Physics Letters},
      volume = {479},
      number = {4},
      pages = {274--278},
      issn = {0009-2614},
      doi = {10/dfqrp5},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409009804},
      urldate = {2019-10-01}
    }
    

24. Optical Manipulation of Microtubules for Directed Biomolecule Assembly. C. Zoica Dinu, T. Chakrabarty, E. Lunsford, C. Mauer, J. Plewa, J. S. Dordick, and D. B. Chrisey, Soft Matter 5(20), 3818–3822 (2009) [PDF] [BibTeX]

     BibTeX: @article{zoicadinuOpticalManipulationMicrotubules2009,
      title = {Optical Manipulation of Microtubules for Directed Biomolecule Assembly},
      author = {Zoica~Dinu, Cerasela and Chakrabarty, Tania and Lunsford, Elaine and Mauer, Christopher and Plewa, Joseph and S.~Dordick, Jonathan and B.~Chrisey, Douglas},
      date = {2009},
      journaltitle = {Soft Matter},
      volume = {5},
      number = {20},
      pages = {3818--3822},
      doi = {10/brsq8p},
      url = {https://pubs.rsc.org/en/content/articlelanding/2009/sm/b904639a},
      urldate = {2019-10-01}
    }
    

2008

1. Propagation of Complex Shaped Ultrafast Pulses in Highly Optically Dense Samples. J. C. Davis, M. R. Fetterman, W. S. Warren, and D. Goswami, The Journal of Chemical Physics 128(15), 154312 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: We examine the propagation of shaped (amplitude- and frequency-modulated) ultrafast laser pulses through optically dense rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation all strongly depend on the laser pulse shape. For example, frequency swept pulses, which produce adiabatic passage in the optically thin limit (independent of the sign of the frequency sweep), behave unexpectedly in optically dense samples. Paraxial Maxwell optical Bloch equations can model our ultrafast pulse propagation results well and provide insight.

    BibTeX: @article{davisPropagationComplexShaped2008,
     title = {Propagation of Complex Shaped Ultrafast Pulses in Highly Optically Dense Samples},
     author = {Davis, J. C. and Fetterman, M. R. and Warren, W. S. and Goswami, D.},
     date = {2008-04-17},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {128},
     number = {15},
     pages = {154312},
     issn = {0021-9606},
     doi = {10/dcn637},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.2894871},
     urldate = {2019-08-14}
   }
   

2. Exploring the Nature of Photo-Damage in Two-photon Excitation by Fluorescence Intensity Modulation. A. K. De and D. Goswami, Journal of Fluorescence 19(2), 381 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: We investigate the relative photo-damage effects during one- and two-photon excitations and demonstrate that there exist fundamental differences in the damage induced by a high repetition rate laser as compared to that of a CW laser. This difference is evident from the degree of enhanced fluorescence intensity achieved by blanking the excitation with an optical chopper. Such an enhancement in fluorescence intensity provides better signal-to-noise ratio that could have immediate applications in multiphoton imaging of live specimens.

    BibTeX: @article{deExploringNaturePhotoDamage2008,
     title = {Exploring the {{Nature}} of {{Photo-Damage}} in {{Two-photon Excitation}} by {{Fluorescence Intensity Modulation}}},
     author = {De, Arijit Kumar and Goswami, Debabrata},
     date = {2008-08-21},
     journaltitle = {Journal of Fluorescence},
     shortjournal = {J Fluoresc},
     volume = {19},
     number = {2},
     pages = {381},
     issn = {1573-4994},
     doi = {10/ck4wnn},
     url = {https://doi.org/10.1007/s10895-008-0405-3},
     urldate = {2019-08-14}
   }
   

3. Nonlinear Optical Response of Carbon Nanotubes Functionalized with a Water Soluble Ink. J. Gupta, given-i=P. C. family=Vijayan given=Prof. C., S. Maurya, and D. Goswami, in (2008) [BibTeX]

    BibTeX: @inproceedings{guptaNonlinearOpticalResponse2008,
     title = {Nonlinear Optical Response of Carbon Nanotubes Functionalized with a Water Soluble Ink},
     author = {Gupta, Jyotsana and family=Vijayan, given=Prof. C., given-i={{Prof}}C and Maurya, Sandeep and Goswami, Debabrata},
     date = {2008-12-01}
   }
   

4. Attachment of Different Donor Groups to a Cryptand for Modulation of Two-Photon Absorption Cross-Section. A. Jana, S. Y. Jang, J.-Y. Shin, A. Kumar De, D. Goswami, D. Kim, and P. K. Bharadwaj, Chemistry – A European Journal 14(34), 10628–10638 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon absorption (TPA) properties of a laterally nonsymmetric aza cryptand with attached side arms have been investigated. This series of Schiff base derivatives supports the mechanistic approach for enhancing the TPA process, which is usually dictated by molecular geometry, π-bridging, delocalization length, and corresponding charge-transfer possibilities. The results described here suggest that on increasing the branching units, the TPA cross-section, σ(2), can be tuned to a larger value. The TPA activity is “switched on” when a metal atom enters the cavity and serves as a conduit of electronic delocalization. The σ(2) value increases as the donor strength increases. The maximum value is obtained on moving from the single-branched system to the nearly threefold symmetry. This serves as a useful synthetic strategy for designing novel octupolar molecules with high σ(2) values. Theoretical calculations at the B3LYP functional with the 6–31G* basis set under DFT formalism provide supporting evidence that the communication between the side arms through the metal d orbital and more ordered geometry of chromophores leads to a smaller HOMO–LUMO gap, which has a great influence upon the electronic properties of the molecules.

    BibTeX: @article{janaAttachmentDifferentDonor2008,
     title = {Attachment of {{Different Donor Groups}} to a {{Cryptand}} for {{Modulation}} of {{Two-Photon Absorption Cross-Section}}},
     author = {Jana, Atanu and Jang, So Young and Shin, Jae-Yoon and Kumar De, Arijit and Goswami, Debabrata and Kim, Dongho and Bharadwaj, Parimal K.},
     date = {2008},
     journaltitle = {Chemistry – A European Journal},
     volume = {14},
     number = {34},
     pages = {10628--10638},
     issn = {1521-3765},
     doi = {10/c5gh7k},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.200801396},
     urldate = {2019-08-14}
   }
   

5. Diaza-18-Crown-6 Based Chromophores for Modulation of Two-Photon Absorption Cross-Section by Metal Ions. A. Jana, A. Kumar De, A. Nag, D. Goswami, and P. K. Bharadwaj, Journal of Organometallic Chemistry 693(7), 1186–1194 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: Two chromophores with diaza-18-crown-6 as receptor have been synthesized in high yields. The electronic structure, one-photon absorption (OPA) spectra, and two-photon absorption (TPA) properties have been studied in detail. When no metal ion is added as input, both show negligible TPA cross-section (σ2). However, in the presence of Zn(II)/Cd(II)/Mg(II)/Ca(II) ion, each exhibits large TPA cross-section value. Binding of metal ion in the receptor increases the symmetric charge transfer leading to large σ2 values. Theoretical calculations at the B3LYP functional with 6-31G∗ and LanL2DZ mixed basis set under DFT formalism support experimental results.

    BibTeX: @article{janaDiaza18crown6BasedChromophores2008,
     title = {Diaza-18-Crown-6 Based Chromophores for Modulation of Two-Photon Absorption Cross-Section by Metal Ions},
     author = {Jana, Atanu and Kumar De, Arijit and Nag, Amit and Goswami, Debabrata and Bharadwaj, Parimal K.},
     date = {2008-04-01},
     journaltitle = {Journal of Organometallic Chemistry},
     shortjournal = {Journal of Organometallic Chemistry},
     volume = {693},
     number = {7},
     pages = {1186--1194},
     issn = {0022-328X},
     doi = {10/cdtg8k},
     url = {http://www.sciencedirect.com/science/article/pii/S0022328X08000466},
     urldate = {2019-08-14}
   }
   

6. Nano Computing. V. Sahni and D. Goswami, (Tata McGraw-Hill Education, 2008) [Abstract] [BibTeX]

   Abstract: Computing at the nanoscale is set to revolutionize computing and our way of life. Nanocomputing will help technologists to meet the quest to pack power of computing into the smallest possible device without compromising on speed or accuracy. This book will help scientists, researchers and professionals in related disciplines to understand the fundamentals of this upcoming domain.

    BibTeX: @book{sahniNanoComputing2008,
     title = {Nano {{Computing}}},
     author = {Sahni, Vishal and Goswami, Debabrata},
     date = {2008},
     eprint = {2YSWGKtuzzsC},
     eprinttype = {googlebooks},
     publisher = {{Tata McGraw-Hill Education}},
     isbn = {978-0-07-133109-8},
     pagetotal = {193}
   }
   

7. Coded Nanoscale Self-Assembly. P. Samineni and D. Goswami, Pramana 71(6), 1345–1351 (2008) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate coded self-assembly in nanostructures using the code seeded at the component level through computer simulations. Defects or cavities occur in all natural assembly processes including crystallization and our simulations capture this essential aspect under surface minimization constraints for self-assembly. Our bottom-up approach to nanostructures would provide a new dimension towards nanofabrication and better understanding of defects and crystallization process.

    BibTeX: @article{samineniCodedNanoscaleSelfassembly2008,
     title = {Coded Nanoscale Self-Assembly},
     author = {Samineni, Prathyush and Goswami, Debabrata},
     date = {2008-12-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {71},
     number = {6},
     pages = {1345--1351},
     issn = {0973-7111},
     doi = {10/dhqk8m},
     url = {https://doi.org/10.1007/s12043-008-0188-8},
     urldate = {2019-08-14}
   }
   

2007

1. Metal Induced Enhancement of Fluorescence and Modulation of Two-Photon Absorption Cross-Section with a Donor–Acceptor–Acceptor–Donor Receptor. S. Das, A. Nag, K. K. Sadhu, D. Goswami, and P. K. Bharadwaj, Journal of Organometallic Chemistry 692(22), 4969–4977 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: A metal ion sensing fluorophore L that exhibits a large two-photon absorption cross-section has been synthesized in good yields. The influences of different metal ion inputs, on the one- and two-photon spectroscopic properties of L, have been investigated. The ligand itself does not show any fluorescence although in presence of a metal ion like Zn(II), Cd(II), Mg(II) or Ca(II), a ∼25 time enhancement of fluorescence is observed. The ligand with symmetrical “donor–acceptor–acceptor–donor” characteristics exhibits a large two-photon absorption cross-section measured by femtosecond open-aperture Z-scan technique at 880nm. However, presence of any of the above metal ions lowers its two-photon absorption cross-section (δ) to different extents at 880nm. Theoretical calculation carried out in DFT formalism on the ligand and its Zn(II) complex corroborate experimental results.

    BibTeX: @article{dasMetalInducedEnhancement2007,
     title = {Metal Induced Enhancement of Fluorescence and Modulation of Two-Photon Absorption Cross-Section with a Donor–Acceptor–Acceptor–Donor Receptor},
     author = {Das, Sanjib and Nag, Amit and Sadhu, Kalyan K. and Goswami, Debabrata and Bharadwaj, Parimal K.},
     date = {2007-10-15},
     journaltitle = {Journal of Organometallic Chemistry},
     shortjournal = {Journal of Organometallic Chemistry},
     volume = {692},
     number = {22},
     pages = {4969--4977},
     issn = {0022-328X},
     doi = {10/fkrn5p},
     url = {http://www.sciencedirect.com/science/article/pii/S0022328X07005244},
     urldate = {2019-08-14}
   }
   

2. Erratum to “High Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities” [Opt. Commun. 261 (2006) 158–162]. D. Goswami, Optics Communications 280(1), 236 (2007) [PDF] [BibTeX]

    BibTeX: @article{goswamiErratumHighSensitive2007,
     title = {Erratum to “{{High}} Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities” [{{Opt}}. {{Commun}}. 261 (2006) 158–162]},
     author = {Goswami, Debabrata},
     date = {2007-12},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {280},
     number = {1},
     pages = {236},
     issn = {00304018},
     doi = {10/bxb2kz},
     url = {https://linkinghub.elsevier.com/retrieve/pii/S0030401807007420},
     urldate = {2019-08-14}
   }
   

3. On the Practicality of Adiabatic Quantum Computing with Optical Schemes. D. Goswami, International Journal of Quantum Information 05(01n02), 179–188 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: A robust implementation of quantum logical gates for a multilevel system is possible through decoherence control under the quantum adiabatic method using simple phase modulated laser pulses. Selective population inversion and Hamiltonian evolution with time through ultrafast pulse shaping techniques essentially amount to adiabatic quantum computing (AQC) instead of the standard unitary transformation. An important aspect of the AQC model is in addressing the atomic or molecular ensemble and hence in robust implementation. We argue that experimental demonstrations of selective population transfer through adiabatic rapid passage form useful adiabatic quantum computing logic. Similarly, a simple Hadamard operation can be demonstrated with phase-modulated laser pulses. Finally, we present a framework to efficiently solve approximate Euclidean Traveling Salesman Problem (Approx-TSP) with bounded error in the AQC model. We present an efficient and intuitive encoding for Approx-TSP in a quantum computing paradigm. Optical approaches to quantum computing have the potential to be used in a distributive sense to defray the present caveat of limited resources and scalability. We present how we make use of such schemes towards practicality issues in AQC. As far as we know, our results are the first realistic demonstration of the possibility of using ensemble states for AQC in multilevel systems.

    BibTeX: @article{goswamiPracticalityAdiabaticQuantum2007,
     title = {On the Practicality of Adiabatic Quantum Computing with Optical Schemes},
     author = {Goswami, Debabrata},
     date = {2007-02-01},
     journaltitle = {International Journal of Quantum Information},
     shortjournal = {Int. J. Quantum Inform.},
     volume = {05},
     pages = {179--188},
     issn = {0219-7499},
     doi = {10/fkvv3x},
     url = {https://www.worldscientific.com/doi/abs/10.1142/S0219749907002621},
     urldate = {2019-08-14},
     issue = {01n02}
   }
   

4. Probing Coherence Aspects of Adiabatic Quantum Computation and Control. D. Goswami, The Journal of Chemical Physics 127(12), 124305 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: Quantum interference between multiple excitation pathways can be used to cancel the couplings to the unwanted, nonradiative channels resulting in robustly controlling decoherence through adiabatic coherent control approaches. We propose a useful quantification of the two-level character in a multilevel system by considering the evolution of the coherent character in the quantum system as represented by the off-diagonal density matrix elements, which switches from real to imaginary as the excitation process changes from being resonant to completely adiabatic. Such counterintuitive results can be explained in terms of continuous population exchange in comparison to no population exchange under the adiabatic condition.

    BibTeX: @article{goswamiProbingCoherenceAspects2007,
     title = {Probing Coherence Aspects of Adiabatic Quantum Computation and Control},
     author = {Goswami, Debabrata},
     date = {2007-09-25},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {127},
     number = {12},
     pages = {124305},
     issn = {0021-9606},
     doi = {10.1063/1.2768954},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.2768954},
     urldate = {2019-08-14}
   }
   

5. Single Experimental Setup for High Sensitive Absorption Coefficient and Optical Nonlinearities Measurements. D. Goswami, in Lasers and Electro-Optics Research at the Cutting Edge (Nova Publishers, 2007) [Abstract] [BibTeX]

   Abstract: It is expected that ongoing advances in optics will revolutionise the 21st century as they began doing in the last quarter of the 20th. Such fields as communications, materials science, computing and medicine are leaping forward based on developments in optics. This series presents leading edge research on optics and lasers from researchers spanning the globe.

    BibTeX: @incollection{goswamiSingleExperimentalSetup2007,
     title = {Single {{Experimental Setup}} for {{High Sensitive Absorption Coefficient}} and {{Optical Nonlinearities Measurements}}},
     booktitle = {Lasers and {{Electro-optics Research}} at the {{Cutting Edge}}},
     author = {Goswami, Debabrata},
     date = {2007},
     publisher = {{Nova Publishers}},
     isbn = {978-1-60021-194-2}
   }
   

6. One-Pot Synthesis of Core-Modified Rubyrin, Octaphyrin, and Dodecaphyrin: Characterization and Nonlinear Optical Properties. R. Kumar, R. Misra, T. K. Chandrashekar, A. Nag, D. Goswami, E. Suresh, and C. H. Suresh, European Journal of Organic Chemistry 2007(27), 4552–4562 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: Modified 26π rubyrin, 36π octaphyrin, and 54π dodecaphyrin systems have been synthesized in moderately good yields through acid-catalyzed condensations of terthiophene diols and tripyrranes. The product distributions are decided both by the acid catalyst concentration and by the nature of the meso substituents. For example, a new isomer of [26]hexaphyrin(1.1.1.1.0.0) (rubyrin) was obtained with 0.3 equiv. of p-toluenesulfonic acid, when the meso substituent was mesityl in at least one of the precursors. A change of the mesityl substituent for a p-methoxy substituent in terthiophene diol resulted in the formation of a [3 + 3 + 3 + 3] condensation product – [54]dodecaphyrin(1.1.1.1.0.0.1.1.1.1.0.0) – in addition to the expected rubyrin. Furthermore, an increase in the acid concentration to 0.6 equiv. resulted in the formation of a new [36]octaphyrin(1.1.1.1.1.1.0.0), in addition to the rubyrin and dodecaphyrin. A single-crystal X-ray analysis of octaphyrin represents the first example of a planar conformation of an octaphyrin with six meso links. In rubyrin 19, one thiophene ring, opposite to the terthiophene subunit, is inverted, while in octaphyrin 30 one pyrrole ring and two thiophene rings are inverted. The various conformational possibilities tested for the unsubstituted dodecaphyrin 28, at semiempirical level, suggest that the most stable conformation is a figure-eight. The final geometry optimization of figure-eight dodecaphyrin was done at the B3LYP/6-31G* level of DFT. Octaphyrins and dodecaphyrins bind trifluoroacetate anion effectively in their diprotonated forms, the binding constants (K) being 638 M–1 for dodecaphyrin 28, and 415 M–1 for octaphyrin 30. Electrochemical data reveal HOMO destabilization with increasing π electron conjugation, consistently with the large red shifts of the absorption bands. Preliminary studies on the use of these expanded porphyrins as third-order NLO materials were followed by measurements of their two-photon absorption (TPA) cross-sections [σ(2)]. The σ(2) values increase upon going from the 26π rubyrins to the 54π dodecaphyrins, confirming our earlier observation that increases in π-conjugated electrons increase the TPA values.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

    BibTeX: @article{kumarOnePotSynthesisCoreModified2007,
     title = {One-{{Pot Synthesis}} of {{Core-Modified Rubyrin}}, {{Octaphyrin}}, and {{Dodecaphyrin}}: {{Characterization}} and {{Nonlinear Optical Properties}}},
     shorttitle = {One-{{Pot Synthesis}} of {{Core-Modified Rubyrin}}, {{Octaphyrin}}, and {{Dodecaphyrin}}},
     author = {Kumar, Rajeev and Misra, Rajneesh and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata and Suresh, Eringathodi and Suresh, Cherumuttathu H.},
     date = {2007},
     journaltitle = {European Journal of Organic Chemistry},
     volume = {2007},
     number = {27},
     pages = {4552--4562},
     issn = {1099-0690},
     doi = {10/bwctt3},
     url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/ejoc.200700466},
     urldate = {2019-08-14}
   }
   

7. Time Comb Pulses Through Ultrafast Pulse Shaping. S. K. K. Kumar and D. Goswami, in Controlling Light with Light: Photorefractive Effects, Photosensitivity, Fiber Gratings, Photonic Materials and More (2007), Paper MB61 (Optical Society of America, 2007), p. MB61 [Abstract] [PDF] [BibTeX]

   Abstract: Time-comb of femtosecond pulses at 1560nm is demonstrated by coupling a pulse-shaper in one arm of Mach-Zehnder interferometer. Time comb data for 5-pulses last 80ps. Such pulse-shaping technique is ideal in simultaneous time-wavelength multiplexing and coherent control.

    BibTeX: @inproceedings{kumarTimeCombPulses2007,
     title = {Time {{Comb Pulses Through Ultrafast Pulse Shaping}}},
     booktitle = {Controlling {{Light}} with {{Light}}: {{Photorefractive Effects}}, {{Photosensitivity}}, {{Fiber Gratings}}, {{Photonic Materials}} and {{More}} (2007), Paper {{MB61}}},
     author = {Kumar, S. K. Karthick and Goswami, D.},
     date = {2007-10-14},
     pages = {MB61},
     publisher = {{Optical Society of America}},
     doi = {10/gf6c9f},
     url = {https://www.osapublishing.org/abstract.cfm?uri=PR-2007-MB61},
     urldate = {2019-08-14},
     eventtitle = {Photorefractive {{Effects}}, {{Photosensitivity}}, {{Fiber Gratings}}, {{Photonic Materials}} and {{More}}}
   }
   

8. Nonlinear Optical Properties of Free Standing Films of PbS Quantum Dots in the Nonresonant Femtosecond Regime. P. A. Kurian, C. Vijayan, A. Nag, and D. Goswami, in Z. Gaburro and S. Cabrini, eds. (2007), p. 66390M [Abstract] [PDF] [BibTeX]

   Abstract: Devices based on optical technology for high speed communication networks require materials with large nonlinear optical response in the ultrafast regime. Nonlinear optical materials have also attracted wide attention as potential candidates for the protection of optical sensors and eyes while handling lasers. Optical limiters have a constant transmittance at low input influence and a decrease in transmittance at higher fluences and are based on a variety of mechanisms such as nonlinear refraction, nonlinear scattering, multiphoton absorption and free carrier absorption. As we go from bulk to nanosized materials especially in the strong quantum confinement regime where radius of the nanoparticle is less than the bulk exciton Bohr radius, the optical nonlinearity is enhanced due to quantum confinement effect. This paper is on the ultrafast nonresonant nonlinearity in free standing films of PbS quantum dots stabilized in a synthetic glue matrix by a simple chemical route which provides flexibility of processing in a variety of physical forms. Optical absorption spectrum shows significant blue shift from the bulk absorption onset indicating strong quantum confinement. PbS quantumdots of mean size 3.3nm are characterized by X-ray diffraction and transmission electron microscopy. The mechanism of nonlinear absorption giving rise to optical limiting is probed using open z-scan technique with laser pulses of 150 fs pulse duration at 780 nm and the results are presented in the nonresonant femtosecond regime. Irradiance dependence on nonlinear absorption are discussed.

    BibTeX: @inproceedings{kurianNonlinearOpticalProperties2007,
     title = {Nonlinear Optical Properties of Free Standing Films of {{PbS}} Quantum Dots in the Nonresonant Femtosecond Regime},
     author = {Kurian, Pushpa Ann and Vijayan, C. and Nag, Amit and Goswami, Debabrata},
     editor = {Gaburro, Zeno and Cabrini, Stefano},
     date = {2007-09-13},
     pages = {66390M},
     location = {{San Diego, California, USA}},
     doi = {10/cntz9g},
     url = {http://proceedings.spiedigitallibrary.org/proceeding.aspx?doi=10.1117/12.733034},
     urldate = {2019-08-14},
     eventtitle = {{{NanoScience}} + {{Engineering}}}
   }
   

9. The Nanoparticle–Protein Complex as a Biological Entity; a Complex Fluids and Surface Science Challenge for the 21st Century. I. Lynch, T. Cedervall, M. Lundqvist, C. Cabaleiro-Lago, S. Linse, and K. A. Dawson, Advances in Colloid and Interface Science 134–135, 167–174 (2007) [Abstract] [PDF] [BibTeX]

   Abstract: The major aim of our current work is to develop a deep understanding of biological effects of nanoparticles and how these effects are mediated by proteins that are adsorbed on the nanoparticles under different biological circumstances. Due to their small size, nanoparticles have distinct properties compared to the bulk form of the same materials, and these properties are rapidly revolutionizing many areas of medicine and technology. However, relatively little is known about the interaction of nanoscale objects with biological systems, as this requires quite different concepts from more established nanoscience. Thus, we have argued that in a biological fluid, proteins associate with nanoparticles, and it is the amount and presentation of the proteins on the surface rather than the particles themselves that are the cause of numerous biological responses. It is this outer layer of proteins that is seen by the biological cells, and leads to their responses. We are developing novel techniques to identify and quantify the proteins that are consistently associated with nanoparticles, as a function of the nanoparticle size, shape, and surface properties, and to correlate the adsorbed protein identities with their association and dissociation rates to and from the nanoparticles. We also seek to understand the degree of conformational change that they undergo upon adsorption to the nanoparticles. In essence, we wish to create “epitope maps” of the protein corona that surrounds nanoparticles in biological solutions, as it is the particle–protein complex that is the biologically active entity.

    BibTeX: @article{lynchNanoparticleProteinComplex2007,
     title = {The Nanoparticle–Protein Complex as a Biological Entity; a Complex Fluids and Surface Science Challenge for the 21st Century},
     author = {Lynch, Iseult and Cedervall, Tommy and Lundqvist, Martin and Cabaleiro-Lago, Celia and Linse, Sara and Dawson, Kenneth A.},
     date = {2007-10-31},
     journaltitle = {Advances in Colloid and Interface Science},
     shortjournal = {Advances in Colloid and Interface Science},
     series = {Surface Forces: Wetting Phenomena, Membrane Separation, Rheology. {{Topical}} Issue in Honour of {{Victor Starov}}},
     volume = {134--135},
     pages = {167--174},
     issn = {0001-8686},
     doi = {10/chq8ff},
     url = {http://www.sciencedirect.com/science/article/pii/S000186860700067X},
     urldate = {2019-10-01}
   }
   

10. A Sensitive Technique for Two-Photon Absorption Measurements: Towards Higher Resolution Microscopy. A. Nag, A. K. De, and D. Goswami, Journal of Physics: Conference Series 80, 012034 (2007) [Abstract] [PDF] [BibTeX]

    Abstract: High repetition rate (HRR) lasers are essential in multiphoton microscopy for satisfactory signal to noise at low average powers. However, HRR lasers generate thermal distortions in samples even with the slightest single photon absorption. Using an optical chopper with HRR lasers ("blanking") we demonstrate a femtosecond z-scan setup that effectively eliminates thermal as well as small linear absorption effects and precisely measures two-photon absorption (TPA) cross-sections of chromophores. Accurate measurement of TPA cross-sections in biologically relevant chromophores is especially important since the TPA spectrum is considerably different in regions with even minute linear absorption. Such blanking measurements with chopper also show enhanced fluorescence efficiency of the chromophores.

     BibTeX: @article{nagSensitiveTechniqueTwoPhoton2007,
      title = {A {{Sensitive Technique}} for {{Two-Photon Absorption Measurements}}: {{Towards Higher Resolution Microscopy}}},
      shorttitle = {A {{Sensitive Technique}} for {{Two-Photon Absorption Measurements}}},
      author = {Nag, Amit and De, Arijit Kr and Goswami, Debabrata},
      date = {2007-09},
      journaltitle = {Journal of Physics: Conference Series},
      shortjournal = {J. Phys.: Conf. Ser.},
      volume = {80},
      pages = {012034},
      issn = {1742-6596},
      doi = {10/bwjg5v},
      url = {https://doi.org/10.1088%2F1742-6596%2F80%2F1%2F012034},
      urldate = {2019-08-14}
    }
    

11. Numerical Recipes 3rd Edition: The Art of Scientific Computing. W. H. Press, S. A. Teukolsky, W. T. Vetterling, and B. P. Flannery, (Cambridge University Press, 2007) [Abstract] [BibTeX]

    Abstract: Co-authored by four leading scientists from academia and industry, Numerical Recipes Third Edition starts with basic mathematics and computer science and proceeds to complete, working routines. Widely recognized as the most comprehensive, accessible and practical basis for scientific computing, this new edition incorporates more than 400 Numerical Recipes routines, many of them new or upgraded. The executable C++ code, now printed in color for easy reading, adopts an object-oriented style particularly suited to scientific applications. The whole book is presented in the informal, easy-to-read style that made earlier editions so popular. Please visit www.nr.com or www.cambridge.org/us/numericalrecipes for more details. More information concerning licenses is available at: www.nr.com/licenses New key features: 2 new chapters, 25 new sections, 25% longer than Second Edition Thorough upgrades throughout the text Over 100 completely new routines and upgrades of many more. New Classification and Inference chapter, including Gaussian mixture models, HMMs, hierarchical clustering, Support Vector MachinesNew Computational Geometry chapter covers KD trees, quad- and octrees, Delaunay triangulation, and algorithms for lines, polygons, triangles, and spheres New sections include interior point methods for linear programming, Monte Carlo Markov Chains, spectral and pseudospectral methods for PDEs, and many new statistical distributions An expanded treatment of ODEs with completely new routines Plus comprehensive coverage of linear algebra, interpolation, special functions, random numbers, nonlinear sets of equations, optimization, eigensystems, Fourier methods and wavelets, statistical tests, ODEs and PDEs, integral equations, and inverse theory

     BibTeX: @book{pressNumericalRecipes3rd2007,
      title = {Numerical {{Recipes}} 3rd {{Edition}}: {{The Art}} of {{Scientific Computing}}},
      shorttitle = {Numerical {{Recipes}} 3rd {{Edition}}},
      author = {Press, William H. and Teukolsky, Saul A. and Vetterling, William T. and Flannery, Brian P.},
      date = {2007-09-06},
      eprint = {1aAOdzK3FegC},
      eprinttype = {googlebooks},
      publisher = {{Cambridge University Press}},
      isbn = {978-0-521-88068-8},
      pagetotal = {1195}
    }
    

2006

1. Dependence of Adiabatic Population Transfer on Pulse Profile. S. Dasgupta, T. Kushwaha, and D. Goswami, Pramana 66(6), 999 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Control of population transfer by rapid adiabatic passage has been an established technique wherein the exact amplitude profile of the shaped pulse is considered to be insignificant. We study the effect of ultrafast shaped pulses for two-level systems, by density-matrix approach. However, we find that adiabaticity depends simultaneously on pulse profile as well as the frequency modulation under non-resonant conditions

    BibTeX: @article{dasguptaDependenceAdiabaticPopulation2006,
     title = {Dependence of Adiabatic Population Transfer on Pulse Profile},
     author = {Dasgupta, S. and Kushwaha, T. and Goswami, D.},
     date = {2006-06-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {66},
     number = {6},
     pages = {999},
     issn = {0973-7111},
     doi = {10/bsg5fd},
     url = {https://doi.org/10.1007/BF02708454},
     urldate = {2019-08-14}
   }
   

2. Zinc(II)- and Copper(I)-Mediated Large Two-Photon Absorption Cross Sections in a Bis-cinnamaldiminato Schiff Base. S. Das, A. Nag, D. Goswami, and P. K. Bharadwaj, Journal of the American Chemical Society 128(2), 402–403 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: A Schiff base ligand has been synthesized by condensing 1,2-diaminobenzene with 4-(dimethylamino)cinnamaldehyde to give a donor−π-acceptor−π-donor system which does not show any two-photon absorption cross section but which does, upon complexation with Zn(II) or Cu(I), exhibit very high two-photon absorption cross sections.

    BibTeX: @article{dasZincIICopper2006,
     title = {Zinc({{II}})- and {{Copper}}({{I}})-{{Mediated Large Two-Photon Absorption Cross Sections}} in a {{Bis-cinnamaldiminato Schiff Base}}},
     author = {Das, Sanjib and Nag, Amit and Goswami, Debabrata and Bharadwaj, Parimal K.},
     date = {2006-01-01},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {128},
     number = {2},
     pages = {402--403},
     issn = {0002-7863},
     doi = {10/bccmmp},
     url = {https://doi.org/10.1021/ja056771q},
     urldate = {2019-08-14}
   }
   

3. Adiabatic Quantum Computation: Coherent Control Back Action. D. Goswami, AIP Conference Proceedings 864(1), 273–294 (2006) [PDF] [BibTeX]

    BibTeX: @article{goswamiAdiabaticQuantumComputation2006,
     title = {Adiabatic {{Quantum Computation}}: {{Coherent Control Back Action}}},
     shorttitle = {Adiabatic {{Quantum Computation}}},
     author = {Goswami, Debabrata},
     date = {2006-11-15},
     journaltitle = {AIP Conference Proceedings},
     shortjournal = {AIP Conference Proceedings},
     volume = {864},
     number = {1},
     pages = {273--294},
     issn = {0094-243X},
     doi = {10/dg98nw},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.2400899},
     urldate = {2019-08-14}
   }
   

4. High Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities. D. Goswami, Optics Communications 261(1), 158–162 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Accurate knowledge of absorption coefficient of a sample is a prerequisite for measuring the third-order optical nonlinearity of materials, which can be a serious limitation for unknown samples. We introduce a method, which measures both the absorption coefficient and the third-order optical nonlinearity of materials with high sensitivity in a single experimental arrangement. We use a dual-beam pump–probe experiment and conventional single-beam z-scan under different conditions to achieve this goal with communication relevant wavelength. We also demonstrate a counterintuitive coupling of the non-interacting probe-beam with the pump-beam in pump–probe z-scan experiment.

    BibTeX: @article{goswamiHighSensitiveMeasurements2006,
     title = {High Sensitive Measurements of Absorption Coefficient and Optical Nonlinearities},
     author = {Goswami, Debabrata},
     date = {2006-05-01},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {261},
     number = {1},
     pages = {158--162},
     issn = {0030-4018},
     doi = {10/ds4qqp},
     url = {http://www.sciencedirect.com/science/article/pii/S0030401805012903},
     urldate = {2019-08-14}
   }
   

5. Ultrafast Pulse Shaping Developments for Quantum Computation. S. K. Karthick Kumar and D. Goswami, in Current Topics in Atomic, Molecular and Optical Physics (WORLD SCIENTIFIC, 2006), pp. 133–141 [Abstract] [PDF] [BibTeX]

   Abstract: This paper is geared to provide some logical essence of our work on various aspects quantum computing through optical approach involving the engineering aspects of ultrafast laser pulse modulation and programmability. Such an effort also includes the hunt for an appropriate physical system for quantum information as we present here.

    BibTeX: @incollection{karthickkumarUltrafastPulseShaping2006,
     title = {Ultrafast Pulse Shaping Developments for Quantum Computation},
     booktitle = {Current {{Topics}} in {{Atomic}}, {{Molecular}} and {{Optical Physics}}},
     author = {Karthick Kumar, S. K. and Goswami, Debabrata},
     date = {2006-12-01},
     pages = {133--141},
     publisher = {{WORLD SCIENTIFIC}},
     doi = {10.1142/9789812772510_0010},
     url = {https://www.worldscientific.com/doi/abs/10.1142/9789812772510_0010},
     urldate = {2019-08-14},
     isbn = {978-981-270-379-8},
     volumes = {0}
   }
   

6. Second-Harmonic Generation from Magnetic Metamaterials. M. W. Klein, C. Enkrich, M. Wegener, and S. Linden, Science 313(5786), 502–504 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: We observe second-harmonic generation from metamaterials composed of split-ring resonators excited at 1.5-micrometer wavelength. Much larger signals are detected when magnetic-dipole resonances are excited, as compared with purely electric-dipole resonances. The experiments are consistent with calculations based on the magnetic component of the Lorentz force exerted on metal electrons—an intrinsic second-harmonic generation mechanism that plays no role in natural materials. This unusual mechanism becomes relevant in our work as a result of the enhancement and the orientation of the local magnetic fields associated with the magnetic-dipole resonances of the split-ring resonators. An array of split gold rings produces a current that exhibits a nonlinear magnetic response to infrared light, confirming predictions. An array of split gold rings produces a current that exhibits a nonlinear magnetic response to infrared light, confirming predictions.

    BibTeX: @article{kleinSecondHarmonicGenerationMagnetic2006,
     title = {Second-{{Harmonic Generation}} from {{Magnetic Metamaterials}}},
     author = {Klein, Matthias W. and Enkrich, Christian and Wegener, Martin and Linden, Stefan},
     date = {2006-07-28},
     journaltitle = {Science},
     volume = {313},
     number = {5786},
     eprint = {16873661},
     eprinttype = {pmid},
     pages = {502--504},
     issn = {0036-8075, 1095-9203},
     doi = {10/d4qxbj},
     url = {https://science.sciencemag.org/content/313/5786/502},
     urldate = {2019-10-01}
   }
   

7. 22π Smaragdyrin Molecular Conjugates with Aromatic Phenylacetylenes and Ferrocenes: Syntheses, Electrochemical, and Photonic Properties. R. Misra, R. Kumar, T. K. Chandrashekar, C. H. Suresh, A. Nag, and D. Goswami, Journal of the American Chemical Society 128(50), 16083–16091 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Syntheses, spectroscopic, electrochemical, and third-order nonlinear optical susceptibilities of a series of 22π smaragdyrins and their corresponding Rh(I) derivatives bearing phenylacetylene substituents and ferrocene-containing substituents are reported. The synthetic strategy involved a [3 + 2] acid-catalyzed oxidative coupling reaction of the appropriate dipyrromethane and oxatripyrrane. The desired meso substituents, such as phenylacetylenylphenyl and the ferrocenes, were incorporated to the dipyrromethane unit prior to the oxidative coupling reaction. The optical absorption, emission characteristics, and the quantum yield of the smaragdyrin conjugates depends on the nature of the substituent, nature of linker group, and the spacer length. Theoretical studies at the DFT level suggest high delocalization of electrons confined to only four of the five available heterocyclic rings for the free bases. However, upon Rh(I) metalation, the π-electron delocalization is extended to all the heterocyclic rings. The two-photon absorption cross section (TPA) values σ(2) measured through the open aperture Z-scan method, increases linearly with enhanced π-electron delocalization for the smaragdyrins containing phenylacetylene substituents. The meta branching of substituents decreases σ(2) values. Introduction of Rh(I) to the smaragdyrin cavity enhances the σ(2) values by about 3−10 orders of magnitude, attributed to the increased aromatic character upon Rh(I) insertion. The calculated molecular electrostatic potential (MESP) and harmonic oscillator model of aromaticity (HOMA) for the free bases and the Rh(I) derivatives justifies such a conclusion. A linear correlation observed for the second oxidation potential of Rh(I) derivatives and corresponding free bases also support the increased aromaticity upon Rh(I) insertion. The electrochemical data for ferrocene-containing smaragdyrins reveal easier ring oxidation by about 50−130 mV and harder ferrocene oxidation by 40−180 mV suggesting electron-donating nature of the ferrocene upon linking with the smaragdyrin π system. The TPA cross section value of 88782 GM observed for 5g represents one of the highest values known for a metalloexpanded porphyrin derivative.

    BibTeX: @article{misra22pSmaragdyrinMolecular2006,
     title = {22π {{Smaragdyrin Molecular Conjugates}} with {{Aromatic Phenylacetylenes}} and {{Ferrocenes}}:\, {{Syntheses}}, {{Electrochemical}}, and {{Photonic Properties}}},
     shorttitle = {22π {{Smaragdyrin Molecular Conjugates}} with {{Aromatic Phenylacetylenes}} and {{Ferrocenes}}},
     author = {Misra, Rajneesh and Kumar, Rajeev and Chandrashekar, Tavarekere K. and Suresh, C. H. and Nag, Amit and Goswami, Debabrata},
     date = {2006-12-01},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {128},
     number = {50},
     pages = {16083--16091},
     issn = {0002-7863},
     doi = {10/ds2r2p},
     url = {https://doi.org/10.1021/ja0628295},
     urldate = {2019-08-14}
   }
   

8. Modified (22π) Smaragdyrins with Large Two-Photon Absorption Cross Section: A Structure Function Correlation. R. Misra, R. Kumar, T. K. Chandrashekar, A. Nag, and D. Goswami, Organic Letters 8(4), 629–631 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon absorption (TPA) cross-section values for a series of 22π smaragdyrins bearing phenylacetylenylphenyl and [(phenylacetylenyl)phenylacetylenyl]phenyl meso links and their Rh(I) derivatives are reported.

    BibTeX: @article{misraModified22pSmaragdyrins2006,
     title = {Modified (22π) {{Smaragdyrins}} with {{Large Two-Photon Absorption Cross Section}}:\, {{A Structure Function Correlation}}},
     shorttitle = {Modified (22π) {{Smaragdyrins}} with {{Large Two-Photon Absorption Cross Section}}},
     author = {Misra, Rajneesh and Kumar, Rajeev and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata},
     date = {2006-02-01},
     journaltitle = {Organic Letters},
     shortjournal = {Org. Lett.},
     volume = {8},
     number = {4},
     pages = {629--631},
     issn = {1523-7060},
     doi = {10/dhmkht},
     url = {https://doi.org/10.1021/ol052809s},
     urldate = {2019-08-14}
   }
   

9. Structure Property Correlations in Alcohols through Two-Photon Absorption Cross-Section Measurements. A. Nag, S. Singh, and D. Goswami, Chemical Physics Letters 430(4), 420–423 (2006) [Abstract] [PDF] [BibTeX]

   Abstract: Two-photon absorption (TPA) cross-sections of neat alcohols are shown to be a femtosecond laser measurable property with useful structure property correlations that are directly correlated to the self-phase modulation of the alcohol in question. The amount of self-phase modulation is shown to be a molecular structure dependent property. The real and the imaginary components of the second-order hyperpolarizability are thus shown to be interrelated. Such TPA measurements prove that it is not possible to predict two-photon absorption properties by simple doubling the wavelengths of one-photon absorption spectra.

    BibTeX: @article{nagStructurePropertyCorrelations2006,
     title = {Structure Property Correlations in Alcohols through Two-Photon Absorption Cross-Section Measurements},
     author = {Nag, Amit and Singh, Sherdeep and Goswami, Debabrata},
     date = {2006-10-30},
     journaltitle = {Chemical Physics Letters},
     shortjournal = {Chemical Physics Letters},
     volume = {430},
     number = {4},
     pages = {420--423},
     issn = {0009-2614},
     doi = {10/dbmk87},
     url = {http://www.sciencedirect.com/science/article/pii/S0009261406013091},
     urldate = {2019-08-14}
   }
   

10. Nanowire Photonics. P. J. Pauzauskie and P. Yang, Materials Today 9(10), 36–45 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: The development of integrated electronic circuitry ranks among the most disruptive and transformative technologies of the 20th century. Even though integrated circuits are ubiquitous in modern life, both fundamental and technical constraints will eventually test the limits of Moore’s law. Nanowire photonic circuitry constructed from myriad one-dimensional building blocks offers numerous opportunities for the development of next-generation optical information processors and spectroscopy. However, several challenges remain before the potential of nanowire building blocks is fully realized. We cover recent advances in nanowire synthesis, characterization, lasing, integration, and the eventual application to relevant technical and scientific questions.

     BibTeX: @article{pauzauskieNanowirePhotonics2006,
      title = {Nanowire Photonics},
      author = {Pauzauskie, Peter J. and Yang, Peidong},
      date = {2006-10-01},
      journaltitle = {Materials Today},
      shortjournal = {Materials Today},
      volume = {9},
      number = {10},
      pages = {36--45},
      issn = {1369-7021},
      doi = {10/cs3g73},
      url = {http://www.sciencedirect.com/science/article/pii/S1369702106716522},
      urldate = {2019-10-01}
    }
    

11. Aromatic Core Modified Decaphyrins with the Largest Two-Photon Absorption Cross-Sections: Syntheses and Characterization. H. Rath, V. Prabhuraja, T. K. Chandrashekar, A. Nag, D. Goswami, and B. S. Joshi, Organic Letters 8(11), 2325–2328 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: Core-modified aromatic decaphyrins with 42π conjugated electrons exhibit the highest two-photon absorption cross-section value (σ2 = 108 000 GM) known for any organic molecule, suggesting possible device applications in the field of nonlinear optics.

     BibTeX: @article{rathAromaticCoreModified2006,
      title = {Aromatic {{Core Modified Decaphyrins}} with the {{Largest Two-Photon Absorption Cross-Sections}}:\, {{Syntheses}} and {{Characterization}}},
      shorttitle = {Aromatic {{Core Modified Decaphyrins}} with the {{Largest Two-Photon Absorption Cross-Sections}}},
      author = {Rath, Harapriya and Prabhuraja, Viswanathan and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata and Joshi, Bhawani S.},
      date = {2006-05-01},
      journaltitle = {Organic Letters},
      shortjournal = {Org. Lett.},
      volume = {8},
      number = {11},
      pages = {2325--2328},
      issn = {1523-7060},
      doi = {10/cwgk39},
      url = {https://doi.org/10.1021/ol060622a},
      urldate = {2019-08-14}
    }
    

12. Calibration of Optical Tweezers with Positional Detection in the Back Focal Plane. S. F. Tolić-Nørrelykke, E. Schäffer, J. Howard, F. S. Pavone, F. Jülicher, and H. Flyvbjerg, Review of Scientific Instruments 77(10), 103101 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: We explain and demonstrate a new method of force and position calibrations for optical tweezers with back-focal-plane photodetection. The method combines power spectral measurements of thermal motion and the response to a sinusoidal motion of a translation stage. It consequently does not use the drag coefficient of the trapped object as an input. Thus, neither the viscosity, nor the size of the trapped object, nor its distance to nearby surfaces needs to be known. The method requires only a low level of instrumentation and can be applied in situ in all spatial dimensions. It is both accurate and precise: true values are returned, with small error bars. We tested this experimentally, near and far from surfaces in the lateral directions. Both position and force calibrations were accurate to within 3%. To calibrate, we moved the sample with a piezoelectric translation stage, but the laser beam could be moved instead, e.g., by acousto-optic deflectors. Near surfaces, this precision requires an improved formula for the hydrodynamical interaction between an infinite plane and a microsphere in nonconstant motion parallel to it. We give such a formula.

     BibTeX: @article{tolic-norrelykkeCalibrationOpticalTweezers2006,
      title = {Calibration of Optical Tweezers with Positional Detection in the Back Focal Plane},
      author = {Tolić-Nørrelykke, Simon F. and Schäffer, Erik and Howard, Jonathon and Pavone, Francesco S. and Jülicher, Frank and Flyvbjerg, Henrik},
      date = {2006-10-01},
      journaltitle = {Review of Scientific Instruments},
      shortjournal = {Review of Scientific Instruments},
      volume = {77},
      number = {10},
      pages = {103101},
      issn = {0034-6748},
      doi = {10/dzq7fk},
      url = {https://aip.scitation.org/doi/full/10.1063/1.2356852},
      urldate = {2019-10-01}
    }
    

13. Optical Trapping and Light-Induced Agglomeration of Gold Nanoparticle Aggregates. Y. Zhang, C. Gu, A. M. Schwartzberg, S. Chen, and J. Z. Zhang, Physical Review B 73(16), 165405 (2006) [Abstract] [PDF] [BibTeX]

    Abstract: This paper demonstrates the optical trapping of micron-sized gold nanoparticle aggregates (GNAs) with a TEM00 mode laser at 532nm and reports the observation of an unusual light-induced agglomeration phenomenon that occurs besides the trapping of the GNAs. The observed agglomerate has a 60–100μm donut-shaped metal microstructure with the rate of formation dependent on the laser power used. Citrate capped gold nanoparticles also show light-induced agglomeration, yielding different sized microstructures from those produced with GNAs. While the observed trapping can be explained by a model including the optical radiation and radiometric forces, the light-induced agglomeration cannot be explained by these two forces alone as the size of the agglomerate is much greater than the waist of the Gaussian beam used in the optical trapping. We attribute the additional cause of the light-induced agglomeration to ion detachment from the surface of the nanoparticles (aggregates) due to light illumination or heating. This is supported by the observation of reversible electrical conductivity changes of the solution of the nanoparticles (aggregates) upon laser illumination or direct heating. Light-induced agglomeration can be useful in the design and fabrication of microstructures from nanomaterials for various device applications.

     BibTeX: @article{zhangOpticalTrappingLightinduced2006,
      title = {Optical Trapping and Light-Induced Agglomeration of Gold Nanoparticle Aggregates},
      author = {Zhang, Yi and Gu, Claire and Schwartzberg, Adam M. and Chen, Shaowei and Zhang, Jin Z.},
      date = {2006-04-06},
      journaltitle = {Physical Review B},
      shortjournal = {Phys. Rev. B},
      volume = {73},
      number = {16},
      pages = {165405},
      doi = {10/bpw2d7},
      url = {https://link.aps.org/doi/10.1103/PhysRevB.73.165405},
      urldate = {2019-10-01}
    }
    

2005

1. Adiabatic Quantum Computing with Phase Modulated Laser Pulses. D. Goswami, Journal of Physics A: Mathematical and General 38(38), L615–L626 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: Implementation of quantum logical gates for multilevel systems is demonstrated through decoherence control under the quantum adiabatic method using simple phase modulated laser pulses. We make use of selective population inversion and Hamiltonian evolution with time to achieve such goals robustly instead of the standard unitary transformation language.

    BibTeX: @article{goswamiAdiabaticQuantumComputing2005,
     title = {Adiabatic Quantum Computing with Phase Modulated Laser Pulses},
     author = {Goswami, Debabrata},
     date = {2005-09-23},
     journaltitle = {Journal of Physics A: Mathematical and General},
     shortjournal = {J. Phys. A: Math. Gen.},
     volume = {38},
     number = {38},
     pages = {L615-L626},
     issn = {0305-4470, 1361-6447},
     doi = {10/cf95fb},
     url = {http://stacks.iop.org/0305-4470/38/i=38/a=L02?key=crossref.595c46dd082aae283e104e33a2aafff9},
     urldate = {2019-08-14}
   }
   

2. Multiphoton Coherent Control in Complex Systems. D. Goswami, Journal of Optics B: Quantum and Semiclassical Optics 7(10), S265–S269 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: Control of multiphoton transitions is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion while the even terms lead to self-induced transparency. The results hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse width.

    BibTeX: @article{goswamiMultiphotonCoherentControl2005,
     title = {Multiphoton Coherent Control in Complex Systems},
     author = {Goswami, Debabrata},
     date = {2005-09},
     journaltitle = {Journal of Optics B: Quantum and Semiclassical Optics},
     shortjournal = {J. Opt. B: Quantum Semiclass. Opt.},
     volume = {7},
     number = {10},
     pages = {S265--S269},
     issn = {1464-4266},
     doi = {10.1088/1464-4266/7/10/009},
     url = {https://doi.org/10.1088%2F1464-4266%2F7%2F10%2F009},
     urldate = {2019-08-14}
   }
   

3. Quantum Computation with Ultrafast Laser Pulse Shaping. D. Goswami, Resonance 10(6), 8–14 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: Quantum computing exploits the quantum mechanical nature of matter to exist in multiple possible states simultaneously. Building up on the digital binary logic of bits, quantum computing is built on the basis of interacting two-level quantum systems or ‘qubits’ that follow the laws of quantum mechanics. Addressability of the quantum system and its fragility to fidelity are the major issues of concern, which if addressed appropriately, will enable this new approach to revolutionize the present form of computing.

    BibTeX: @article{goswamiQuantumComputationUltrafast2005,
     title = {Quantum Computation with Ultrafast Laser Pulse Shaping},
     author = {Goswami, Debabrata},
     date = {2005-06-01},
     journaltitle = {Resonance},
     shortjournal = {Reson},
     volume = {10},
     number = {6},
     pages = {8--14},
     issn = {0973-712X},
     doi = {10/c3f36s},
     url = {https://doi.org/10.1007/BF02895790},
     urldate = {2019-08-14}
   }
   

4. Heterodimers of Nanoparticles: Formation at a Liquid−Liquid Interface and Particle-Specific Surface Modification by Functional Molecules. H. Gu, Z. Yang, J. Gao, C. K. Chang, and B. Xu, Journal of the American Chemical Society 127(1), 34–35 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: On the basis of a fundamental property of nanoparticles, the self-assembling at a liquid−liquid interface to form “colloidosomes”, a heterogeneous reaction takes place on the exposed surface of the nanoparticles to produce the heterodimers of two distinct nanospheres, which can be modified by two different functional molecules in a particle-specific manner.

    BibTeX: @article{guHeterodimersNanoparticlesFormation2005,
     title = {Heterodimers of {{Nanoparticles}}:\, {{Formation}} at a {{Liquid}}−{{Liquid Interface}} and {{Particle-Specific Surface Modification}} by {{Functional Molecules}}},
     shorttitle = {Heterodimers of {{Nanoparticles}}},
     author = {Gu, Hongwei and Yang, Zhimou and Gao, Jinhao and Chang, C. K. and Xu, Bing},
     date = {2005-01-01},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {127},
     number = {1},
     pages = {34--35},
     issn = {0002-7863},
     doi = {10/dxqtsd},
     url = {https://doi.org/10.1021/ja045220h},
     urldate = {2019-10-01}
   }
   

5. Expanding the Optical Trapping Range of Gold Nanoparticles. P. M. Hansen, V. K. Bhatia, N. Harrit, and L. Oddershede, Nano Letters 5(10), 1937–1942 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate stable three-dimensional (3D) single-beam optical trapping of gold nanoparticles with diameters between 18 and 254 nm. Three-dimensional power spectral analysis reveals that, for nanoparticles with diameters less than 100 nm, the trap stiffness is proportional to the volume of the particle. For larger particles, the trap stiffness still increases with size, however, less steeply. Finally, we provide numbers for the largest forces exertable on gold nanoparticles.

    BibTeX: @article{hansenExpandingOpticalTrapping2005,
     title = {Expanding the {{Optical Trapping Range}} of {{Gold Nanoparticles}}},
     author = {Hansen, Poul Martin and Bhatia, Vikram Kjøller and Harrit, Niels and Oddershede, Lene},
     date = {2005-10-01},
     journaltitle = {Nano Letters},
     shortjournal = {Nano Lett.},
     volume = {5},
     number = {10},
     pages = {1937--1942},
     issn = {1530-6984},
     doi = {10.1021/nl051289r},
     url = {https://doi.org/10.1021/nl051289r},
     urldate = {2019-10-01}
   }
   

6. Novel Optical and Statistical Methods Reveal Colloid–Wall Interactions Inconsistent with DLVO and Lifshitz Theories. P. M. Hansen, J. K. Dreyer, J. Ferkinghoff-Borg, and L. Oddershede, Journal of Colloid and Interface Science 287(2), 561–571 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: We present an experimental method based on video microscopy to perform nanometer scale position detection of a micrometer bead in the direction along the propagation of the detection light. Using the same bead for calibration and detection significantly improves the in depth resolution in comparison to video microscopy methods from literature. This method is used together with an optical trap to measure interaction potentials between a glass surface and colloids made of polystyrene or silica at different electrolyte concentrations. The results are confirmed by an independent method where the optical trap is used in connection with a quadrant photodiode. Also, we present a maximum likelihood analysis method which considerably improves the spatial resolution of interaction potentials by optimizing the underlying potential function to fit all observed position distributions. The measured interaction potentials agree well with DLVO theory for small electrolyte concentrations; however, for larger electrolyte concentrations the potentials differ qualitatively from both DLVO and Lifshitz theory.

    BibTeX: @article{hansenNovelOpticalStatistical2005,
     title = {Novel Optical and Statistical Methods Reveal Colloid–Wall Interactions Inconsistent with {{DLVO}} and {{Lifshitz}} Theories},
     author = {Hansen, Poul Martin and Dreyer, Jakob Kisbye and Ferkinghoff-Borg, Jesper and Oddershede, Lene},
     date = {2005-07-15},
     journaltitle = {Journal of Colloid and Interface Science},
     shortjournal = {Journal of Colloid and Interface Science},
     volume = {287},
     number = {2},
     pages = {561--571},
     issn = {0021-9797},
     doi = {10/dnc43n},
     url = {http://www.sciencedirect.com/science/article/pii/S0021979705001104},
     urldate = {2019-10-01}
   }
   

7. Core-Modified Expanded Porphyrins with Large Third-Order Nonlinear Optical Response. H. Rath, J. Sankar, V. PrabhuRaja, T. K. Chandrashekar, A. Nag, and D. Goswami, Journal of the American Chemical Society 127(33), 11608–11609 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: The third-order nonlinear optical response through measurement of two-photon absorption cross-sections (TPACS) for aromatic core-modified expanded porphyrin analogues by a femtosecond open aperture Z-scan method is reported. The values reported here are among the largest known so far in the literature for any organic molecules.

    BibTeX: @article{rathCoreModifiedExpandedPorphyrins2005,
     title = {Core-{{Modified Expanded Porphyrins}} with {{Large Third-Order Nonlinear Optical Response}}},
     author = {Rath, Harapriya and Sankar, Jeyaraman and PrabhuRaja, Viswanathan and Chandrashekar, Tavarekere K. and Nag, Amit and Goswami, Debabrata},
     date = {2005-08-24},
     journaltitle = {Journal of the American Chemical Society},
     shortjournal = {J. Am. Chem. Soc.},
     volume = {127},
     number = {33},
     pages = {11608--11609},
     issn = {0002-7863},
     doi = {10/c2tqsv},
     url = {https://doi.org/10.1021/ja0537575},
     urldate = {2019-08-14}
   }
   

8. Polarization-Induced Modulation of a Femtosecond Nonlinear Process. A. Srivastava and D. Goswami, Physics Letters A 341(5), 523–526 (2005) [Abstract] [PDF] [BibTeX]

   Abstract: We present experimental evidence of laser-induced polarization preference for the highly nonlinear phenomenon of supercontinuum generation. Such results have been arrived through the choice of isotropic and anisotropic materials interacting with femtosecond laser pulses of changing ellipticity. Experimental evidence of additional polarization effects is also present in anisotropic materials. Laser polarization emerges as an important control parameter that exhibits counterintuitive dependence in generating the corresponding high-order nonlinear phenomenon.

    BibTeX: @article{srivastavaPolarizationinducedModulationFemtosecond2005,
     title = {Polarization-Induced Modulation of a Femtosecond Nonlinear Process},
     author = {Srivastava, Alok and Goswami, Debabrata},
     date = {2005-06-27},
     journaltitle = {Physics Letters A},
     shortjournal = {Physics Letters A},
     volume = {341},
     number = {5},
     pages = {523--526},
     issn = {0375-9601},
     doi = {10/crsvpk},
     url = {http://www.sciencedirect.com/science/article/pii/S0375960105006584},
     urldate = {2019-08-14}
   }
   

2004

1. Power Spectrum Analysis for Optical Tweezers. K. Berg-Sørensen and H. Flyvbjerg, Review of Scientific Instruments 75(3), 594–612 (2004) [PDF] [BibTeX]

    BibTeX: @article{berg-sorensenPowerSpectrumAnalysis2004,
     title = {Power Spectrum Analysis for Optical Tweezers},
     author = {Berg-Sørensen, Kirstine and Flyvbjerg, Henrik},
     date = {2004-02-18},
     journaltitle = {Review of Scientific Instruments},
     shortjournal = {Review of Scientific Instruments},
     volume = {75},
     number = {3},
     pages = {594--612},
     issn = {0034-6748},
     doi = {10/cbss66},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.1645654},
     urldate = {2019-10-01}
   }
   

2. Towards Efficiently Solving Quantum Traveling Salesman Problem. D. Goswami, H. Karnick, P. Jain, and H. K. Maji, (2004) [Abstract] [PDF] [BibTeX]

   Abstract: We present a framework for efficiently solving Approximate Traveling Salesman Problem (Approximate TSP) for Quantum Computing Models. Existing representations of TSP introduce extra states which do not correspond to any permutation. We present an efficient and intuitive encoding for TSP in quantum computing paradigm. Using this representation and assuming a Gaussian distribution on tour-lengths, we give an algorithm to solve Approximate TSP (Euclidean) within BQP resource bounds. Generalizing this strategy for any distribution, we present an oracle based Quantum Algorithm to solve Approximate TSP. We present a realization of the oracle in the quantum counterpart of PP.

    BibTeX: @unpublished{goswamiEfficientlySolvingQuantum2004,
     title = {Towards {{Efficiently Solving Quantum Traveling Salesman Problem}}},
     author = {Goswami, Debabrata and Karnick, Harish and Jain, Prateek and Maji, Hemanta K.},
     date = {2004-11-02},
     eprint = {quant-ph/0411013},
     eprinttype = {arxiv},
     url = {http://arxiv.org/abs/quant-ph/0411013},
     urldate = {2019-08-14}
   }
   

3. Directed Assembly and Rupture Mechanics of Colloidal Aggregates. J. P. Pantina and E. M. Furst, Langmuir 20(10), 3940–3946 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: The macroscopic rheological behavior of colloidal gels arises from the micromechanical properties of the gel backbone, which are governed by nanoscale particle interactions. These colloidal interactions have been commonly understood in terms of the Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. Recent work has shown, however, that nonidealities, such as surface roughness and charge nonuniformity, may cause the particle interactions to significantly deviate from DLVO predictions at near-contact separations. Here we present novel techniques for directing the assembly of colloidal aggregates that mimic the gel backbone, based on optical micromanipulation of multiple particles using laser tweezers. This also provides an in situ method for measuring near-contact interactions via single-bond rupture forces. We find that PMMA particles aggregated in the presence of nonorganic salts exhibit interparticle bond strengths more than 10 times greater than those predicted by DLVO theory. However, good agreement is found with DLVO predictions when the anionic surfactant sodium dodecyl sulfate (SDS) is used as the flocculant.

    BibTeX: @article{pantinaDirectedAssemblyRupture2004,
     title = {Directed {{Assembly}} and {{Rupture Mechanics}} of {{Colloidal Aggregates}}},
     author = {Pantina, John P. and Furst, Eric M.},
     date = {2004-05-01},
     journaltitle = {Langmuir},
     shortjournal = {Langmuir},
     volume = {20},
     number = {10},
     pages = {3940--3946},
     issn = {0743-7463},
     doi = {10/btmtnz},
     url = {https://doi.org/10.1021/la0364338},
     urldate = {2019-10-01}
   }
   

4. Single Experimental Setup for High Sensitive Absorption Coefficient and Optical Nonlinearities Measurements. A. Sharan, S. A. Hosseini, and D. Goswami, (2004) [Abstract] [PDF] [BibTeX]

   Abstract: Accurate knowledge of absorption coefficient of a sample is a prerequisite for measuring the third order optical nonlinearity of materials, which can be a serious limitation for unknown samples. We introduce a method, which measures both the absorption coefficient and the third order optical nonlinearity of materials with high sensitivity in a single experimental arrangement. We use a dual-beam pump-probe experiment and conventional single-beam z-scan under different conditions to achieve this goal. We also demonstrate a counterintuitive coupling of the non-interacting probe-beam with the pump-beam in pump-probe z-scan experiment.

    BibTeX: @unpublished{sharanSingleExperimentalSetup2004,
     title = {Single {{Experimental Setup}} for {{High Sensitive Absorption Coefficient}} and {{Optical Nonlinearities Measurements}}},
     author = {Sharan, A. and Hosseini, S. Abbas and Goswami, D.},
     date = {2004-01-01},
     eprint = {physics/0401003},
     eprinttype = {arxiv},
     url = {http://arxiv.org/abs/physics/0401003},
     urldate = {2019-08-14}
   }
   

5. Laser Polarization Effects in Supercontinuum Generation. A. Srivastava and D. Goswami, (2004) [Abstract] [PDF] [BibTeX]

   Abstract: We present experimental evidence of a fourth order process in electric field in supercontinuum generation. We also show laser induced polarization preference in the supercontinuum generating media. These results have become possible through the choice of isotropic and anisotropic samples interacting with ultrashort laser pulses of changing ellipticity. Laser polarization emerges as an important control parameter for the highly nonlinear phenomenon of supercontinuum generation.

    BibTeX: @unpublished{srivastavaLaserPolarizationEffects2004,
     title = {Laser {{Polarization Effects}} in {{Supercontinuum Generation}}},
     author = {Srivastava, Alok and Goswami, Debabrata},
     date = {2004-02-22},
     eprint = {quant-ph/0402163},
     eprinttype = {arxiv},
     url = {http://arxiv.org/abs/quant-ph/0402163},
     urldate = {2019-08-14}
   }
   

6. Equilibrium Cluster Formation in Concentrated Protein Solutions and Colloids. A. Stradner, H. Sedgwick, F. Cardinaux, W. C. K. Poon, S. U. Egelhaaf, and P. Schurtenberger, Nature 432(7016), 492–495 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: Controlling interparticle interactions, aggregation and cluster formation is of central importance in a number of areas, ranging from cluster formation in various disease processes to protein crystallography and the production of photonic crystals. Recent developments in the description of the interaction of colloidal particles with short-range attractive potentials have led to interesting findings including metastable liquid–liquid phase separation and the formation of dynamically arrested states (such as the existence of attractive and repulsive glasses, and transient gels)1,2,3,4,5,6,7. The emerging glass paradigm has been successfully applied to complex soft-matter systems, such as colloid–polymer systems8 and concentrated protein solutions9. However, intriguing problems like the frequent occurrence of cluster phases remain10,11,12,13. Here we report small-angle scattering and confocal microscopy investigations of two model systems: protein solutions and colloid–polymer mixtures. We demonstrate that in both systems, a combination of short-range attraction and long-range repulsion results in the formation of small equilibrium clusters. We discuss the relevance of this finding for nucleation processes during protein crystallization, protein or DNA self-assembly and the previously observed formation of cluster and gel phases in colloidal suspensions12,13,14,15,16,17.

    BibTeX: @article{stradnerEquilibriumClusterFormation2004,
     title = {Equilibrium Cluster Formation in Concentrated Protein Solutions and Colloids},
     author = {Stradner, Anna and Sedgwick, Helen and Cardinaux, Frédéric and Poon, Wilson C. K. and Egelhaaf, Stefan U. and Schurtenberger, Peter},
     date = {2004-11},
     journaltitle = {Nature},
     shortjournal = {Nature},
     volume = {432},
     number = {7016},
     pages = {492--495},
     issn = {1476-4687},
     doi = {10/dgtd9p},
     url = {https://www.nature.com/articles/nature03109},
     urldate = {2019-10-01}
   }
   

7. Anomalous Diffusion in Living Yeast Cells. I. M. Tolić-Nørrelykke, E.-L. Munteanu, G. Thon, L. Oddershede, and K. Berg-Sørensen, Physical Review Letters 93(7), 078102 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: The viscoelastic properties of the cytoplasm of living yeast cells were investigated by studying the motion of lipid granules naturally occurring in the cytoplasm. A large frequency range of observation was obtained by a combination of video-based and laser-based tracking methods. At time scales from 10−4 to 102 s, the granules typically perform subdiffusive motion with characteristics different from previous measurements in living cells. This subdiffusive behavior is thought to be due to the presence of polymer networks and membranous structures in the cytoplasm. Consistent with this hypothesis, we observe that the motion becomes less subdiffusive upon actin disruption.

    BibTeX: @article{tolic-norrelykkeAnomalousDiffusionLiving2004,
     title = {Anomalous {{Diffusion}} in {{Living Yeast Cells}}},
     author = {Tolić-Nørrelykke, Iva Marija and Munteanu, Emilia-Laura and Thon, Genevieve and Oddershede, Lene and Berg-Sørensen, Kirstine},
     date = {2004-08-13},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {93},
     number = {7},
     pages = {078102},
     doi = {10/d7hp3v},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.93.078102},
     urldate = {2019-10-01}
   }
   

8. MatLab Program for Precision Calibration of Optical Tweezers. I. M. Tolić-Nørrelykke, K. Berg-Sørensen, and H. Flyvbjerg, Computer Physics Communications 159(3), 225–240 (2004) [Abstract] [PDF] [BibTeX]

   Abstract: Optical tweezers are used as force transducers in many types of experiments. The force they exert in a given experiment is known only after a calibration. Computer codes that calibrate optical tweezers with high precision and reliability in the (x,y)-plane orthogonal to the laser beam axis were written in MatLab (MathWorks Inc.) and are presented here. The calibration is based on the power spectrum of the Brownian motion of a dielectric bead trapped in the tweezers. Precision is achieved by accounting for a number of factors that affect this power spectrum. First, cross-talk between channels in 2D position measurements is tested for, and eliminated if detected. Then, the Lorentzian power spectrum that results from the Einstein–Ornstein–Uhlenbeck theory, is fitted to the low-frequency part of the experimental spectrum in order to obtain an initial guess for parameters to be fitted. Finally, a more complete theory is fitted, a theory that optionally accounts for the frequency dependence of the hydrodynamic drag force and hydrodynamic interaction with a nearby cover slip, for effects of finite sampling frequency (aliasing), for effects of anti-aliasing filters in the data acquisition electronics, and for unintended “virtual” filtering caused by the position detection system. Each of these effects can be left out or included as the user prefers, with user-defined parameters. Several tests are applied to the experimental data during calibration to ensure that the data comply with the theory used for their interpretation: Independence of x- and y-coordinates, Hooke’s law, exponential distribution of power spectral values, uncorrelated Gaussian scatter of residual values. Results are given with statistical errors and covariance matrix. Program summary Title of program: tweezercalib Catalogue identifier: ADTV Program obtainable from: CPC Program Library, Queen’s University of Belfast, N. Ireland. Program Summary URL: http://cpc.cs.qub.ac.uk/summaries/ADTV Computer for which the program is designed and others on which it has been tested: General computer running MatLab (MathWorks Inc.). Programming language used: MatLab (MathWorks Inc.). Uses “Optimization Toolbox” and “Statistics Toolbox”. Memory required to execute with typical data: Of order 4 times the size of the data file. High speed storage required: None No. of lines in distributed program, including test data, etc.: 133183 No. of bytes in distributed program, including test data, etc.: 1043674 Distribution format: tar gzip file Nature of physical problem: Calibrate optical tweezers with precision by fitting theory to experimental power spectrum of position of bead doing Brownian motion in incompressible fluid, possibly near microscope cover slip, while trapped in optical tweezers. Thereby determine spring constant of optical trap and conversion factor for arbitrary-units-to-nanometers for detection system. Method of solution: Elimination of cross-talk between quadrant photo-diode’s output channels for positions (optional). Check that distribution of recorded positions agrees with Boltzmann distribution of bead in harmonic trap. Data compression and noise reduction by blocking method applied to power spectrum. Full accounting for hydrodynamic effects: Frequency-dependent drag force and interaction with nearby cover slip (optional). Full accounting for electronic filters (optional), for “virtual filtering” caused by detection system (optional). Full accounting for aliasing caused by finite sampling rate (optional). Standard non-linear least-squares fitting. Statistical support for fit is given, with several plots suitable for inspection of consistency and quality of data and fit. Restrictions on the complexity of the problem: Data should be positions of bead doing Brownian motion while held by optical tweezers. For high precision in final results, data should be time series measured over a long time, with sufficiently high experimental sampling rate: The sampling rate should be well above the characteristic frequency of the trap, the so-called corner frequency. Thus, the sampling frequency should typically be larger than 10 kHz. The Fast Fourier Transform applied requires the time series to contain 2n data points, and long measurement time is obtained with n>12–15. Finally, the optics should be set to ensure a harmonic trapping potential in the range of positions visited by the bead. The fitting procedure checks for harmonic potential. Typical running time: (Tens of) minutes Unusual features of the program: None References: The theoretical underpinnings for the procedure are found in [K. Berg-Sørensen, H. Flyvbjerg, Rev. Sci. Instrum. 75 (3) (2004) 594].

    BibTeX: @article{tolic-norrelykkeMatLabProgramPrecision2004,
     title = {{{MatLab}} Program for Precision Calibration of Optical Tweezers},
     author = {Tolić-Nørrelykke, Iva Marija and Berg-Sørensen, Kirstine and Flyvbjerg, Henrik},
     date = {2004-06-01},
     journaltitle = {Computer Physics Communications},
     shortjournal = {Computer Physics Communications},
     volume = {159},
     number = {3},
     pages = {225--240},
     issn = {0010-4655},
     doi = {10/fgkfzg},
     url = {http://www.sciencedirect.com/science/article/pii/S0010465504001043},
     urldate = {2019-10-01}
   }
   

2003

1. Gelation in Model Colloid−Polymer Mixtures. J. Bergenholtz, W. C. K. Poon, and M. Fuchs, Langmuir 19(10), 4493–4503 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Mode coupling theory (MCT) is used to model gel formation in mixtures of colloidal particles and nonadsorbing polymer. The polymer induces an effective, short-range attraction among the colloids, which is modeled by a depletion attraction of the Asakura−Oosawa form. This enables the MCT to be solved analytically for dilute systems, leading to a prediction, free of adjustable parameters, of the location of the gel boundary in the phase diagram. For concentrated systems, a simple mapping is suggested that makes a previous theory for Yukawa interactions applicable to colloid−polymer mixtures. The results are compared against Monte Carlo simulations and experiments on model systems. Excellent agreement is observed at high colloid concentrations, where the theory predicts melting of glassy structures on addition of small amounts of polymer. Further addition of polymer causes gelation, in semiquantitative accord with experimental data at moderate to high colloid concentrations. However, at lower concentrations the theory is unable to capture the onset of transient gelation.

    BibTeX: @article{bergenholtzGelationModelColloid2003,
     title = {Gelation in {{Model Colloid}}−{{Polymer Mixtures}}},
     author = {Bergenholtz, J. and Poon, W. C. K. and Fuchs, M.},
     date = {2003-05-01},
     journaltitle = {Langmuir},
     shortjournal = {Langmuir},
     volume = {19},
     number = {10},
     pages = {4493--4503},
     issn = {0743-7463},
     doi = {10/bdsbxs},
     url = {https://doi.org/10.1021/la0340089},
     urldate = {2019-10-01}
   }
   

2. Self-Organization in Biological Systems. S. Camazine, J.-L. Deneubourg, N. R. Franks, J. Sneyd, E. Bonabeau, and G. Theraula, (Princeton University Press, 2003) [Abstract] [BibTeX]

   Abstract: The synchronized flashing of fireflies at night. The spiraling patterns of an aggregating slime mold. The anastomosing network of army-ant trails. The coordinated movements of a school of fish. Researchers are finding in such patterns–phenomena that have fascinated naturalists for centuries–a fertile new approach to understanding biological systems: the study of self-organization. This book, a primer on self-organization in biological systems for students and other enthusiasts, introduces readers to the basic concepts and tools for studying self-organization and then examines numerous examples of self-organization in the natural world. Self-organization refers to diverse pattern formation processes in the physical and biological world, from sand grains assembling into rippled dunes to cells combining to create highly structured tissues to individual insects working to create sophisticated societies. What these diverse systems hold in common is the proximate means by which they acquire order and structure. In self-organizing systems, pattern at the global level emerges solely from interactions among lower-level components. Remarkably, even very complex structures result from the iteration of surprisingly simple behaviors performed by individuals relying on only local information. This striking conclusion suggests important lines of inquiry: To what degree is environmental rather than individual complexity responsible for group complexity? To what extent have widely differing organisms adopted similar, convergent strategies of pattern formation? How, specifically, has natural selection determined the rules governing interactions within biological systems? Broad in scope, thorough yet accessible, this book is a self-contained introduction to self-organization and complexity in biology–a field of study at the forefront of life sciences research.

    BibTeX: @book{camazineSelforganizationBiologicalSystems2003,
     title = {Self-Organization in {{Biological Systems}}},
     author = {Camazine, Scott and Deneubourg, Jean-Louis and Franks, Nigel R. and Sneyd, James and Bonabeau, Eric and Theraula, Guy},
     date = {2003-09-17},
     eprint = {BIqCDwAAQBAJ},
     eprinttype = {googlebooks},
     publisher = {{Princeton University Press}},
     isbn = {978-0-691-11624-2},
     pagetotal = {546}
   }
   

3. Optical Computing. D. Goswami, Resonance 8(6), 56–71 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Optics has been used in computing for a number of years but the main emphasis has been and continues to be to link portions of computers, for communications, or more intrinsically in devices that have some optical application or component (optical pattern recognition, etc). Optical digital computers are still some years away, however a number of devices that can ultimately lead to real optical computers have already been manufactured, including optical logic gates, optical switches, optical interconnections, and optical memory. The most likely near-term optical computer will really be a hybrid composed of traditional architectural design along with some portions that can perform some functional operations in optical mode.

    BibTeX: @article{goswamiOpticalComputing2003,
     title = {Optical Computing},
     author = {Goswami, Debabrata},
     date = {2003-06-01},
     journaltitle = {Resonance},
     shortjournal = {Reson},
     volume = {8},
     number = {6},
     pages = {56--71},
     issn = {0973-712X},
     doi = {10/d5qtw5},
     url = {https://doi.org/10.1007/BF02837869},
     urldate = {2019-08-14}
   }
   

4. Optical Pulse Shaping Approaches to Coherent Control. D. Goswami, Physics Reports 374(6), 385–481 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: The last part of the twentieth century has experienced a huge resurge of activity in the field of coherent light–matter interaction, more so in attempting to exert control over such interactions. Birth of coherent control was originally spurred by the theoretical understanding of the quantum interferences that lead to energy randomization and experimental developments in ultrafast laser spectroscopy. The theoretical predictions on control of reaction channels or energy randomization processes are still more dramatic than the experimental demonstrations, though this gap between the two is consistently reducing over the recent years with realistic theoretical models and technological developments. Experimental demonstrations of arbitrary optical pulse shaping have made some of the previously impracticable theoretical predictions possible to implement. Starting with the simple laser modulation schemes to provide proof-of-the-principle demonstrations, feedback loop pulse shaping systems have been developed that can actively manipulate some atomic and molecular processes. This tremendous experimental boost of optical pulse shaping developments has prospects and implications into many more new directions, such as quantum computing and terabit/sec data communications. This review captures certain aspects and impacts of optical pulse shaping into the fast developing areas of coherent control and other related fields. Currently available reviews focus on one or the other detailed aspects of coherent control, and the reader will be referred to such details as and when necessary for issues that are dealt in brief here. We will focus on the current issues including control of intramolecular dynamics and make connections to the future concepts, such as, quantum computation, biomedical applications, etc.

    BibTeX: @article{goswamiOpticalPulseShaping2003,
     title = {Optical Pulse Shaping Approaches to Coherent Control},
     author = {Goswami, Debabrata},
     date = {2003-02-01},
     journaltitle = {Physics Reports},
     shortjournal = {Physics Reports},
     volume = {374},
     number = {6},
     pages = {385--481},
     issn = {0370-1573},
     doi = {10/fwwrc5},
     url = {http://www.sciencedirect.com/science/article/pii/S0370157302004805},
     urldate = {2019-08-14}
   }
   

5. Ultrafast Pulse Shaping Approaches to Quantum Computing. D. Goswami, (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Quantum computing exploits the quantum-mechanical nature of matter to exist in multiple possible states simultaneously. This new approach promises to revolutionize the present form of computing. As an approach to quantum computing, we discuss ultrafast laser pulse shaping, in particular, the acousto-optic modulator based Fourier-Transform pulse-shaper, which has the ability to modulate tunable high power ultrafast laser pulses. We show that optical pulse shaping is an attractive route to quantum computing since shaped pulses can be transmitted over optical hardware and the same infrastructure can be used for computation and optical information transfer. We also address the problem of extending coherence-times for optically induced processes.

    BibTeX: @unpublished{goswamiUltrafastPulseShaping2003,
     title = {Ultrafast {{Pulse Shaping Approaches}} to {{Quantum Computing}}},
     author = {Goswami, Debabrata},
     date = {2003-12-24},
     eprint = {quant-ph/0312192},
     eprinttype = {arxiv},
     url = {http://arxiv.org/abs/quant-ph/0312192},
     urldate = {2019-08-14}
   }
   

6. Control of Supercontinuum Generation with Polarization of Incident Laser Pulses. A. Srivastava and D. Goswami, Applied Physics B 77(2), 325–328 (2003) [Abstract] [PDF] [BibTeX]

   Abstract: Supercontinuum generation is dependent on the polarization state of the incident laser. The polarization of the generated supercontinuum is the same as that of the incident laser. The magnitude of the generated supercontinuum depends on the polarization of the incident laser and increases as the polarization changes from circular to linear, irrespective of the nature of the sample, be it isotropic, anisotropic, or chiral. In all samples, the polarization dependence indicates a preference for the linear component of the incident laser beam. The anisotropic sample shows an additional difference in the generated supercontinuum for the two perpendicular directions of the incident laser polarization.

    BibTeX: @article{srivastavaControlSupercontinuumGeneration2003,
     title = {Control of Supercontinuum Generation with Polarization of Incident Laser Pulses},
     author = {Srivastava, A. and Goswami, D.},
     date = {2003-09-01},
     journaltitle = {Applied Physics B},
     shortjournal = {Appl Phys B},
     volume = {77},
     number = {2},
     pages = {325--328},
     issn = {1432-0649},
     doi = {10/bhqfj6},
     url = {https://doi.org/10.1007/s00340-003-1243-2},
     urldate = {2019-08-14}
   }
   

2002

1. Decoherence Control in Quantum Computing with Simple Chirped Pulses. D. Goswami, Pramana 59(2), 235–242 (2002) [Abstract] [PDF] [BibTeX]

   Abstract: We show how the use of optimally shaped pulses to guide the time evolution of a system (‘coherent control’) can be an effective approach towards quantum computation logic. We demonstrate this with selective control of decoherence for a multilevel system with a simple linearly chirped pulse. We use a multiphoton density-matrix approach to explore the effects of ultrafast shaped pulses for two-level systems that do not have a single photon resonance, and show that many multiphoton results are surprisingly similar to the single-photon results. Finally, we choose two specific chirped pulses: one that always generates inversion and the other that always generates self-induced transparency to demonstrate an ensemble CNOT gate.

    BibTeX: @article{goswamiDecoherenceControlQuantum2002,
     title = {Decoherence Control in Quantum Computing with Simple Chirped Pulses},
     author = {Goswami, Debabrata},
     date = {2002-08-01},
     journaltitle = {Pramana},
     shortjournal = {Pramana - J Phys},
     volume = {59},
     number = {2},
     pages = {235--242},
     issn = {0973-7111},
     doi = {10/bv363m},
     url = {https://doi.org/10.1007/s12043-002-0113-5},
     urldate = {2019-08-14}
   }
   

2. Erratum: Laser Phase Modulation Approaches towards Ensemble Quantum Computing [Phys. Rev. Lett.0031–9007PRLTAO \textbf88 , 177901 (2002)]. D. Goswami, Physical Review Letters 89(27), 279901 (2002) [PDF] [BibTeX]

    BibTeX: @article{goswamiErratumLaserPhase2002,
     title = {Erratum: {{Laser Phase Modulation Approaches}} towards {{Ensemble Quantum Computing}} [{{Phys}}. {{Rev}}. {{Lett}}.0031–{{9007PRLTAO}} {\textbf{88}} , 177901 (2002)]},
     shorttitle = {Erratum},
     author = {Goswami, Debabrata},
     date = {2002-12-18},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {89},
     number = {27},
     pages = {279901},
     issn = {0031-9007, 1079-7114},
     doi = {10/chtkbd},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.89.279901},
     urldate = {2019-08-14}
   }
   

3. Laser Phase Modulation Approaches towards Ensemble Quantum Computing. D. Goswami, Physical Review Letters 88(17), 177901 (2002) [Abstract] [PDF] [BibTeX]

   Abstract: Selective control of decoherence is demonstrated for a multilevel system by generalizing the instantaneous phase of any chirped pulse as individual terms of a Taylor series expansion. In the case of a simple two-level system, all odd terms in the series lead to population inversion, while the even terms lead to self-induced transparency. These results also hold for multiphoton transitions that do not have any lower-order photon resonance or any intermediate virtual state dynamics within the laser pulse width. Such results form the basis of a robustly implementable CNOT gate.

    BibTeX: @article{goswamiLaserPhaseModulation2002,
     title = {Laser {{Phase Modulation Approaches}} towards {{Ensemble Quantum Computing}}},
     author = {Goswami, Debabrata},
     date = {2002-04-15},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {88},
     number = {17},
     pages = {177901},
     doi = {10/c339br},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.88.177901},
     urldate = {2019-08-14}
   }
   

4. High Sensitive Measurement of Absorption Coefficient and Optical Nonlinearities with a Single Experimental Setup. S. A. Hosseini, A. Sharan, and D. Goswami, (2002) [Abstract] [PDF] [BibTeX]

   Abstract: Accurate knowledge of absorption coefficient of a sample is a prerequisite for measuring the third order optical nonlinearity of materials, which could become a serious limitation for unknown samples. We introduce a new method, which measures both the absorption coefficient and the third order optical nonlinearity of materials with high sensitivity in a single experimental setup. We use a dual-beam pump-probe experiment under different conditions to achieve this goal. We also demonstrate a counterintuitive coupling of the non-interacting probe-beam with the pump-beam in pump-probe z-scan experiment.

    BibTeX: @unpublished{hosseiniHighSensitiveMeasurement2002,
     title = {High {{Sensitive Measurement}} of {{Absorption Coefficient}} and {{Optical Nonlinearities}} with a {{Single Experimental Setup}}},
     author = {Hosseini, S. Abbas and Sharan, A. and Goswami, D.},
     date = {2002-01-08},
     eprint = {physics/0201009},
     eprinttype = {arxiv},
     url = {http://arxiv.org/abs/physics/0201009},
     urldate = {2019-08-14}
   }
   

5. Novel Femtosecond Setup for High Sensitive Absorption Coefficient and Optical Nonlinearities Measurements. S. A. Hosseini, A. Sharan, and D. Goswami, in Nonlinear Optics: Materials, Fundamentals and Applications (2002), Paper MB4 (Optical Society of America, 2002), p. MB4 [Abstract] [PDF] [BibTeX]

   Abstract: We introduce a new method to measure both absorption coefficient and third order optical nonlinearity of materials with high sensitivity in a single experimental setup. A dual-beam pump-probe experiment achieves this goal but shows a counterintuitive coupling.

    BibTeX: @inproceedings{hosseiniNovelFemtosecondSetup2002,
     title = {Novel {{Femtosecond Setup}} for {{High Sensitive Absorption Coefficient}} and {{Optical Nonlinearities Measurements}}},
     booktitle = {Nonlinear {{Optics}}: {{Materials}}, {{Fundamentals}} and {{Applications}} (2002), Paper {{MB4}}},
     author = {Hosseini, S. Abbas and Sharan, A. and Goswami, D.},
     date = {2002-07-29},
     pages = {MB4},
     publisher = {{Optical Society of America}},
     doi = {10/gf6c9t},
     url = {https://www.osapublishing.org/abstract.cfm?uri=NLO-2002-MB4},
     urldate = {2019-08-14},
     eventtitle = {Nonlinear {{Optics}}: {{Materials}}, {{Fundamentals}} and {{Applications}}}
   }
   

6. Prospects of Ultrafast Pulse Shaping. A. Sharan and D. Goswami, Current Science 82(1), 30–37 (2002) [Abstract] [PDF] [BibTeX]

   Abstract: Availability of femtosecond solid-state lasers around the world has spurred a lot of technological activity in the femtosecond timescale and has also given us a tool to probe and gain more insight into the fundamentals of physics, chemistry and biology. An eventual prospect of controlling and manipulating some of the hitherto impossible tasks, can perhaps now be dreamt of. In this review we give a brief account of some of the promising techniques for ultrafast laser pulse shaping and then list some of the exciting prospects.

    BibTeX: @article{sharanProspectsUltrafastPulse2002,
     title = {Prospects of Ultrafast Pulse Shaping},
     author = {Sharan, Alok and Goswami, Debabrata},
     date = {2002},
     journaltitle = {Current Science},
     volume = {82},
     number = {1},
     eprint = {24105924},
     eprinttype = {jstor},
     pages = {30--37},
     issn = {0011-3891},
     url = {https://www.jstor.org/stable/24105924},
     urldate = {2019-08-14}
   }
   

2001

1. Fast-Frequency-Hopping Modulation and Detection Demonstration. M. R. Fetterman, J. C. Davis, H.-S. Tan, W. Yang, D. Goswami, J.-K. Rhee, and W. S. Warren, JOSA B 18(9), 1372–1376 (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate fast-frequency-hopping modulation that exploits the unique features of acousto-optic-modulator based laser pulse shaping and the spectrally and temporally resolved upconversion technique (STRUT) pulse-characterization method. These pulses have been specifically designed so that they can be characterized by the STRUT, without any processing of the STRUT data set. We present examples of complex fast-frequency-hopping laser pulses that have been generated and characterized by our pulse-shaping system and STRUT. We discuss the theoretical limitations on the data rate that can be obtained with such a technique.

    BibTeX: @article{fettermanFastfrequencyhoppingModulationDetection2001,
     title = {Fast-Frequency-Hopping Modulation and Detection Demonstration},
     author = {Fetterman, M. R. and Davis, J. C. and Tan, H.-S. and Yang, W. and Goswami, D. and Rhee, J.-K. and Warren, W. S.},
     date = {2001-09-01},
     journaltitle = {JOSA B},
     shortjournal = {J. Opt. Soc. Am. B, JOSAB},
     volume = {18},
     number = {9},
     pages = {1372--1376},
     issn = {1520-8540},
     doi = {10/bqpmmt},
     url = {https://www.osapublishing.org/josab/abstract.cfm?uri=josab-18-9-1372},
     urldate = {2019-08-14}
   }
   

2. Multiphoton Control with Ultrafast Pulse Shaping. D. Goswami and S. A. Hosseini, in Optical Fiber Communication Conference and International Conference on Quantum Information (OSA, 2001), p. PA29 [Abstract] [PDF] [BibTeX]

   Abstract: A multiphoton density-matrix approach explores the effects of ultrafast shaped pulses for two-level systems that do not have a single photon resonance, and show that many multiphoton results are surprisingly similar to the single-photon results. These conditions thus allow extending the single-photon coherent control ideas to develop multiphoton coherent control.

    BibTeX: @inproceedings{goswamiMultiphotonControlUltrafast2001,
     title = {Multiphoton {{Control}} with {{Ultrafast Pulse Shaping}}},
     booktitle = {Optical {{Fiber Communication Conference}} and {{International Conference}} on {{Quantum Information}}},
     author = {Goswami, Debabrata and Hosseini, Syed Abbas},
     date = {2001},
     pages = {PA29},
     publisher = {{OSA}},
     location = {{Rochester, New York}},
     doi = {10/gf6c92},
     url = {https://www.osapublishing.org/abstract.cfm?uri=ICQI-2001-PA29},
     urldate = {2019-08-14},
     eventtitle = {International {{Conference}} on {{Quantum Information}}},
     isbn = {978-1-55752-654-0}
   }
   

3. Coherent Control of Multiphoton Transitions with Femtosecond Pulse Shaping. S. A. Hosseini and D. Goswami, Physical Review A 64(3), 033410 (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We explore the effects of ultrafast shaped pulses for two-level systems that do not have a single-photon resonance, by developing a multiphoton density-matrix approach. We take advantage of the fact that the dynamics of the intermediate virtual states are absent within our laser pulse time scales. Under these conditions, the multiphoton results are similar to those for a single photon, and it is possible to extend the single-photon coherent control ideas to develop multiphoton coherent control.

    BibTeX: @article{hosseiniCoherentControlMultiphoton2001,
     title = {Coherent Control of Multiphoton Transitions with Femtosecond Pulse Shaping},
     author = {Hosseini, S. Abbas and Goswami, Debabrata},
     date = {2001-08-09},
     journaltitle = {Physical Review A},
     shortjournal = {Phys. Rev. A},
     volume = {64},
     number = {3},
     pages = {033410},
     doi = {10/ffjx3v},
     url = {https://link.aps.org/doi/10.1103/PhysRevA.64.033410},
     urldate = {2019-08-14}
   }
   

4. Conditions for Soliton-Like Wave Propagation in Pockels and Photorefractive Media. S. A. Hosseini, S. M. Mahdavi, and D. Goswami, (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We study the conditions for soliton-like wave propagation in the Photorefractive (PR) and electro-optic (i.e., Pockels) material, by using Nonlinear Schrodinger (NLS) equation. The complete NLS equation is solved analytically and numerically by transforming it into the phase space. Our results clearly show the existence of both the dark and bright solitary solutions for the PR medium. Interestingly, however, we find only one bright solitary solution in the Pockels case and there is no evidence of any dark solitary solution.

    BibTeX: @unpublished{hosseiniConditionsSolitonLikeWave2001,
     title = {Conditions for {{Soliton-Like Wave Propagation}} in {{Pockels}} and {{Photorefractive Media}}},
     author = {Hosseini, S. Abbas and Mahdavi, S. M. and Goswami, Debabrata},
     date = {2001-04-03},
     eprint = {physics/0104012},
     eprinttype = {arxiv},
     url = {http://arxiv.org/abs/physics/0104012},
     urldate = {2019-08-14}
   }
   

5. High-Ratio Electro-optical Data Compression for Massive Accessing Networks Using AOM-based Ultrafast Pulse Shaping. W. Yang, M. R. Fetterman, D. Goswami, and W. S. Warren, Journal of Optical Communications 22(1), 15–18 (2001) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate the compression of a 3.5 Mbit/s electronic data packet into an optical data packet with 700-Gbit/s effective data rate. The compressed optical data packet can be subsequently decompressed in the optical domain using lump dispersion devices. Combined with high speed optical add-drops [1-5], this high ratio data compression technique enables thousands of electronic end-users to share the bandwidthabundant optical channel directly and simultaneously.

    BibTeX: @article{yangHighratioElectroopticalData2001,
     title = {High-Ratio {{Electro-optical Data Compression}} for {{Massive Accessing Networks Using AOM-based Ultrafast Pulse Shaping}}},
     author = {Yang, Weiguo and Fetterman, Matthew R. and Goswami, Debabrata and Warren, Warren S.},
     date = {2001},
     journaltitle = {Journal of Optical Communications},
     volume = {22},
     number = {1},
     pages = {15--18},
     issn = {2191-6322},
     doi = {10/gf6c93},
     url = {https://www.degruyter.com/dg/viewarticle/j$002fjoc.2001.22.1$002fjoc.2001.22.1.15$002fjoc.2001.22.1.15.xml},
     urldate = {2019-08-14}
   }
   

2000

1. Driving Wave Packet Recurrences with Optimally Modulated Laser Pulses. B. M. Goodson, D. Goswami, H. Rabitz, and W. S. Warren, The Journal of Chemical Physics 112(11), 5081–5090 (2000) [Abstract] [PDF] [BibTeX]

   Abstract: In the weak-field limit, laser pulses optimized to induce vibrational wave packet recurrences in excited state potentials were calculated for Morse oscillators and for a real system [the X\mkern1mu1Σ+ and A\mkern1mu3Π(1) states of IBr]. The performance of the optimized pulses was studied via simulated wave packet propagation. Such optimal light fields may be computationally generated given only the form of the electronic potential surfaces, knowledge of the particular ground state supplying population, and simple molecular constants. Thus it should be possible to use the modulation of light fields experimentally optimized to achieve recurrences in order to obtain substantial information regarding previously uncharacterized potential surfaces in both diatomic and polyatomic molecules. Moreover, it should be possible to generalize this approach to the strong-field limit.

    BibTeX: @article{goodsonDrivingWavePacket2000,
     title = {Driving Wave Packet Recurrences with Optimally Modulated Laser Pulses},
     author = {Goodson, Boyd M. and Goswami, Debabrata and Rabitz, Herschel and Warren, Warren S.},
     date = {2000-03-03},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {112},
     number = {11},
     pages = {5081--5090},
     issn = {0021-9606},
     doi = {10/cgpwmf},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.481062},
     urldate = {2019-08-14}
   }
   

2. Suppression of Supercontinuum Generation with Circularly Polarized Light. A. S. Sandhu, S. Banerjee, and D. Goswami, Optics Communications 181(1), 101–107 (2000) [Abstract] [PDF] [BibTeX]

   Abstract: Controlling a nonlinear process such as supercontinuum generation (SG) with the polarization-state of laser is an important demonstration of laser selectivity. We show that the threshold for SG and the total amount of supercontinuum generated depends on incident laser polarization for isotropic samples. Irrespective of the nature of the samples chosen, SG efficiency decreases as the incident laser polarization changes from linear to circular and thus, provides the first experimental demonstration of the suppression of SG with circularly polarized light. The ratio of the overall SG between the linear and circular polarization (i.e., measure of suppression) undergoes an intensity dependent decrease from large initial values to asymptotic limits, irrespective of samples.

    BibTeX: @article{sandhuSuppressionSupercontinuumGeneration2000,
     title = {Suppression of Supercontinuum Generation with Circularly Polarized Light},
     author = {Sandhu, Arvinder S and Banerjee, Sudeep and Goswami, Debabrata},
     date = {2000-07-01},
     journaltitle = {Optics Communications},
     shortjournal = {Optics Communications},
     volume = {181},
     number = {1},
     pages = {101--107},
     issn = {0030-4018},
     doi = {10/brwfhq},
     url = {http://www.sciencedirect.com/science/article/pii/S0030401800007525},
     urldate = {2019-08-14}
   }
   

1999

1. Altering Excitation Dynamics in Optically Dense Media Using Shaped Ultrafast Laser Pulses. J. C. Davis, M. R. Fetterman, D. Goswami, Wei Guo Yang, D. Keusters, and W. S. Warren, in Technical Digest. Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference (1999), pp. 107–108 [Abstract] [BibTeX]

   Abstract: Summary form only given. We study the interaction between intense (50 MW peak power), shaped ultrafast laser pulses and optically dense samples of Rb vapor. In particular, we concentrate our attention on laser pulses with a the complex hyperbolic secant envelope, or equivalently, a sech electric field envelope with a tanh frequency sweep. In order to produce and characterize the shaped laser pulses used in our experiments, we exploited several new technologies: amplified, shaped laser pulses were generated using an acousto-optic modulator-based system combined with a chirped-pulse regenerative amplifier. The amplitude and phase of these pulses were then characterized by the STRUT (spectrally and temporally resolved upconversion technique). The STRUT was used to measure the laser pulses both before and after propagating through Rb vapor. Examples of such experimental STRUT images are presented. The complex sech pulse was selected because, in optically thin media, only it and rectangular pulses give complete analytical solutions to the Bloch equations. This shape has been found to generate complete population inversion over a well-defined and amplitude-insensitive bandwidth. In optically dense samples the excited state dynamics are not so straightforward. We have found, both in experiments and theoretically, that the extent and character of the population inversion is related to the frequency sweep of the laser pulses as does the amount of residual excited population after the pulse and any subsequent stimulated emission.

    BibTeX: @inproceedings{davisAlteringExcitationDynamics1999,
     title = {Altering Excitation Dynamics in Optically Dense Media Using Shaped Ultrafast Laser Pulses},
     booktitle = {Technical {{Digest}}. {{Summaries}} of {{Papers Presented}} at the {{Quantum Electronics}} and {{Laser Science Conference}}},
     author = {Davis, J. C. and Fetterman, M. R. and Goswami, D. and {Wei Guo Yang} and Keusters, D. and Warren, W. S.},
     date = {1999-05},
     pages = {107--108},
     doi = {10/cbtw6x},
     eventtitle = {Technical {{Digest}}. {{Summaries}} of {{Papers Presented}} at the {{Quantum Electronics}} and {{Laser Science Conference}}}
   }
   

2. Propagation of Complex Laser Pulses in Optically Dense Media. M. R. Fetterman, J. C. Davis, D. Goswami, W. Yang, and W. S. Warren, Physical Review Letters 82(20), 3984–3987 (1999) [Abstract] [PDF] [BibTeX]

   Abstract: Ultrafast laser pulses with complex envelopes (amplitude and frequency modulated) are used to excite an optically dense column of rubidium vapor. Pulse reshaping, stimulated emission dynamics, and residual electronic excitation in the Rb vapor are all shown to depend strongly on the laser pulse shape. Pulses that produce adiabatic passage in the optically thin limit exhibit more complex behavior in optically thick samples, including an unexpected dependence on the sign of the frequency sweep. Numerical solutions of the Maxwell-Bloch equations are shown to account for our results.

    BibTeX: @article{fettermanPropagationComplexLaser1999,
     title = {Propagation of {{Complex Laser Pulses}} in {{Optically Dense Media}}},
     author = {Fetterman, M. R. and Davis, J. C. and Goswami, D. and Yang, W. and Warren, W. S.},
     date = {1999-05-17},
     journaltitle = {Physical Review Letters},
     shortjournal = {Phys. Rev. Lett.},
     volume = {82},
     number = {20},
     pages = {3984--3987},
     doi = {10/dgk8pv},
     url = {https://link.aps.org/doi/10.1103/PhysRevLett.82.3984},
     urldate = {2019-08-14}
   }
   

3. Real-Time Adaptive Amplitude Feedback in an AOM-based Ultrafast Optical Pulse Shaping System. Weiguo Yang, Feng Huang, M. R. Fetterman, J. C. Davis, D. Goswami, and W. S. Warren, IEEE Photonics Technology Letters 11(12), 1665–1667 (1999) [Abstract] [BibTeX]

   Abstract: We demonstrate real-time adaptive amplitude feedback in an AOM-based ultrafast optical pulse shaping system operating at /spl lambda/=1550 nm wavelength for optical communication applications. At the optimized feedback depth, a simple negative feedback algorithm converges in fewer than 10 iterations to within 5% of the target shape. This technique may be very useful for many applications including spectrum-sliced WDM.

    BibTeX: @article{weiguoyangRealtimeAdaptiveAmplitude1999,
     title = {Real-Time Adaptive Amplitude Feedback in an {{AOM-based}} Ultrafast Optical Pulse Shaping System},
     author = {{Weiguo Yang} and {Feng Huang} and Fetterman, M. R. and Davis, J. C. and Goswami, D. and Warren, W. S.},
     date = {1999-12},
     journaltitle = {IEEE Photonics Technology Letters},
     volume = {11},
     number = {12},
     pages = {1665--1667},
     issn = {1041-1135},
     doi = {10/dvrf7c}
   }
   

1998

1. Generation of Amplified Shaped Pulses for Highly Adiabatic Excitation. M. Fetterman, D. Goswami, D. Keusters, J.-K. Rhee, and W. S. Warren, in Ultrafast Phenomena XI, T. Elsaesser, J. G. Fujimoto, D. A. Wiersma, and W. Zinth, eds., Springer Series in Chemical Physics (Springer Berlin Heidelberg, 1998), pp. 24–26 [Abstract] [BibTeX]

   Abstract: Complex amplified pulses, including al ps, 100 µJ tanh-swept sech pulse for adiabatic inversion, are generated experimentally. STRUT detection verifies the modulation and follows the dynamics induced by such pulses in Rb vapor. Applications to production of spin-polarized gases for medical imaging are discussed.

    BibTeX: @inproceedings{fettermanGenerationAmplifiedShaped1998,
     title = {Generation of Amplified Shaped Pulses for Highly Adiabatic Excitation},
     booktitle = {Ultrafast {{Phenomena XI}}},
     author = {Fetterman, Matthew and Goswami, Debabrata and Keusters, Dorine and Rhee, June-Koo and Warren, Warren S.},
     editor = {Elsaesser, Thomas and Fujimoto, James G. and Wiersma, Douwe A. and Zinth, Wolfgang},
     date = {1998},
     series = {Springer {{Series}} in {{Chemical Physics}}},
     pages = {24--26},
     publisher = {{Springer Berlin Heidelberg}},
     isbn = {978-3-642-72289-9}
   }
   

2. Ultrafast Pulse Shaping: Amplification and Characterization. M. R. Fetterman, D. Goswami, D. Keusters, W. Yang, J.-K. Rhee, and W. S. Warren, Optics Express 3(10), 366–375 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate high-resolution amplified pulse shaping using an acousto-optic modulator (AOM) at a center-wavelength of 795nm. The output pulses have energy of 200μJ/pulse and a transform-limited pulsewidth of 150fs. A spectral modulation of over 40 features is achieved in a single pulse. We characterize the pulses using the STRUT (Spectrally and Temporally Resolved Upconversion Technique). Using predistortion techniques, we demonstrate that the pulses can be shaped in amplitude and phase. We create a complex pulse shape with hyperbolic secant amplitude and hyperbolic tangent frequency sweep, which is useful for applications in adiabatic rapid passage experiments.

    BibTeX: @article{fettermanUltrafastPulseShaping1998,
     title = {Ultrafast Pulse Shaping: Amplification and Characterization},
     shorttitle = {Ultrafast Pulse Shaping},
     author = {Fetterman, M. R. and Goswami, D. and Keusters, D. and Yang, W. and Rhee, J.-K. and Warren, W. S.},
     date = {1998-11-09},
     journaltitle = {Optics Express},
     shortjournal = {Opt. Express, OE},
     volume = {3},
     number = {10},
     pages = {366--375},
     issn = {1094-4087},
     doi = {10/czfxs8},
     url = {https://www.osapublishing.org/oe/abstract.cfm?uri=oe-3-10-366},
     urldate = {2019-08-14}
   }
   

3. Interference Model for Back-Focal-Plane Displacement Detection in Optical Tweezers. F. Gittes and C. F. Schmidt, Optics Letters 23(1), 7–9 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: The lateral position of an optically trapped object in a microscope can be monitored with a quadrant photodiode to within nanometers or better by measurement of intensity shifts in the back focal plane of the lens that is collimating the outgoing laser light. This detection is largely independent of the position of the trap in the field of view. We provide a model for the essential mechanism of this type of detection, giving a simple, closed-form analytic solution with simplifying assumptions. We identify intensity shifts as first-order far-field interference between the outgoing laser beam and scattered light from the trapped particle, where the latter is phase advanced owing to the Gouy phase anomaly. This interference also reflects momentum transfer to the particle, giving the spring constant of the trap. Our response formula is compared with the results of experiments.

    BibTeX: @article{gittesInterferenceModelBackfocalplane1998,
     title = {Interference Model for Back-Focal-Plane Displacement Detection in Optical Tweezers},
     author = {Gittes, Frederick and Schmidt, Christoph F.},
     date = {1998-01-01},
     journaltitle = {Optics Letters},
     shortjournal = {Opt. Lett., OL},
     volume = {23},
     number = {1},
     pages = {7--9},
     issn = {1539-4794},
     doi = {10/bjwpvd},
     url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-23-1-7},
     urldate = {2019-10-01}
   }
   

4. Laser Enhanced NMR Spectroscopy, Revisited. W. S. Warren, D. Goswami, and S. Mayr, Molecular Physics 93(3), 371–375 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: Experimental investigations of the effects of moderately powerful (10–20 W cm-2) offresonant continuous lasers on NMR spectra provide no evidence for the B (3) field recently proposed, or for any other mechanism which depends on the light polarization. Observed 1H and 13C line shifts with argon-ion laser irradiation for the molecule p -methoxyphenyliminocamphor mostly can be explained by heating effects. Residual shifts due to other mechanisms appear to be at most 0·1 Hz (5% of the linewidth). One mechanism which could account for residual shifts of this magnitude is differences between NMR frequencies in the excited (triplet) and ground electronic states, although our data have insufficient resolution to make definitive claims. However, it seems unlikely that this effect can be made sufficiently large to give practical resolution enhancements without massive heating.

    BibTeX: @article{warrenLaserEnhancedNMR1998,
     title = {Laser Enhanced {{NMR}} Spectroscopy, Revisited},
     author = {Warren, W. S. and Goswami, Debabrata and Mayr, Suzanne},
     date = {1998-02-01},
     journaltitle = {Molecular Physics},
     volume = {93},
     number = {3},
     pages = {371--375},
     issn = {0026-8976},
     doi = {10/c692sm},
     url = {https://doi.org/10.1080/002689798169041},
     urldate = {2019-08-14}
   }
   

5. Optical-Wavelength-Domain Code Division Multiplexing Using an AOM-based Ultrafast Optical Pulse-Shaping Approach. W. Yang, J. Davis, D. Goswami, M. Fetterman, and W. S. Warren, in All-Optical Networking: Architecture, Control, and Management Issues (International Society for Optics and Photonics, 1998), 3531, pp. 80–86 [Abstract] [PDF] [BibTeX]

   Abstract: Optical wavelength domain code-division multiplexing access (WD-CDMA) using an AOM-based ultrafast optical pulse shaping approach is proposed and demonstrated experimentally at 1550 nm. This new multiplexing technique utilizes wavelength domain codes that are essentially different optical spectral patterns in order to achieve CDMA. In addition to the advantages of the conventional CDMA technique, WD-CDMA can make full use of the entire optical bandwidth without requiring faster optical switches or modulators. This approach also drastically reduces sensitivity to fiber dispersion. Experimentally, we demonstrate an optical spectral encoder using ultrafast optical pulse shaping with 16 wavelength bits over an optical bandwidth of 5 THz. The spectrally-encoded optical pulse generated with the spectral encoder is then decoded with different WD-CDMA codes in the spectral domain. Different code-division channels can thus extract their own bit information while sharing the same spectral-encoded laser pulse as their common carrier. These spectral-encoded pulses are shown using the cross- correlation technique to be confined within a time slot of 15 ps. A larger number of WD bits is also achievable with our system.

    BibTeX: @inproceedings{yangOpticalwavelengthdomainCodeDivision1998,
     title = {Optical-Wavelength-Domain Code Division Multiplexing Using an {{AOM-based}} Ultrafast Optical Pulse-Shaping Approach},
     booktitle = {All-{{Optical Networking}}: {{Architecture}}, {{Control}}, and {{Management Issues}}},
     author = {Yang, Weiguo and Davis, Jennifer and Goswami, Debabrata and Fetterman, Matthew and Warren, Warren S.},
     date = {1998-10-07},
     volume = {3531},
     pages = {80--86},
     publisher = {{International Society for Optics and Photonics}},
     doi = {10/chgwnm},
     url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/3531/0000/Optical-wavelength-domain-code-division-multiplexing-using-an-AOM-based/10.1117/12.327047.short},
     urldate = {2019-08-14},
     eventtitle = {All-{{Optical Networking}}: {{Architecture}}, {{Control}}, and {{Management Issues}}}
   }
   

6. Rapid Ultrafine-Tunable Optical Delay Line at the 1.55-Μm Wavelength. W. Yang, D. Keusters, D. Goswami, and W. S. Warren, Optics Letters 23(23), 1843–1845 (1998) [Abstract] [PDF] [BibTeX]

   Abstract: A fast, ultrafine-tunable delay line at 1550 nm is demonstrated by use of acousto-optic pulse shaping. Delays of up to 30 ps can be achieved without any optical readjustment. The delay is linear to the rf center frequency applied to the acousto-optic modulator and is fully electronic. It takes only 3 µs to switch between different time slots, irrespective of the time separation in the tuning range of 30 ps; for a smaller tuning range the tuning speed can be faster. The tuning resolution and range depend on the choice of system parameters. The pulse energy can be regulated by rf power.

    BibTeX: @article{yangRapidUltrafinetunableOptical1998,
     title = {Rapid Ultrafine-Tunable Optical Delay Line at the 1.55-Μm Wavelength},
     author = {Yang, Weiguo and Keusters, Dorine and Goswami, Debabrata and Warren, Warren S.},
     date = {1998-12-01},
     journaltitle = {Optics Letters},
     shortjournal = {Opt. Lett., OL},
     volume = {23},
     number = {23},
     pages = {1843--1845},
     issn = {1539-4794},
     doi = {10/fq4dfs},
     url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-23-23-1843},
     urldate = {2019-08-14}
   }
   

1997

1. Protein Dynamics Derived from Clusters of Crystal Structures. Biophysical Journal 73(6), 2891–2896 (1997) [Abstract] [PDF] [BibTeX]

   Abstract: A method is presented to mathematically extract concerted structural transitions in proteins from collections of crystal structures. The "essential dynamics" procedure is used to filter out small-amplitude fluctuations from such a set of structures; the remaining large conformational changes describe motions such as those important for the uptake/release of substrate/ligand and in catalytic reactions. The method is applied to sets of x-ray structures for a number of proteins, and the results are compared with the results from essential dynamics as applied to molecular dynamics simulations of those proteins. A significant degree of similarity is found, thereby providing a direct experimental basis for the application of such simulations to the description of large concerted motions in proteins.

    BibTeX: @article{vanaaltenProteinDynamicsDerived1997,
     title = {Protein Dynamics Derived from Clusters of Crystal Structures},
     author = {},
     date = {1997-12-01},
     journaltitle = {Biophysical Journal},
     shortjournal = {Biophysical Journal},
     volume = {73},
     number = {6},
     pages = {2891--2896},
     issn = {0006-3495},
     doi = {10/bkftm3},
     url = {http://www.sciencedirect.com/science/article/pii/S0006349597783176},
     urldate = {2019-10-01}
   }
   

2. Fast and Ultra-Fine Tunable Optical Delay Line at λ = 1.55 Μm Wavelength. W. Yang, D. Keusters, D. Goswami, and W. S. Warren, in (1997) [BibTeX]

    BibTeX: @inproceedings{yangFastUltrafineTunable1997,
     title = {Fast and Ultra-Fine Tunable Optical Delay Line at λ = 1.55 Μm Wavelength},
     author = {Yang, W. and Keusters, D. and Goswami, D. and Warren, W. S.},
     date = {1997-12-15},
     location = {{Princeton University Center for Ultrafast Laser Application}},
     eventtitle = {{{CULA Kick-off Meeting}}}
   }
   

1994

1. Effects of Pulses with Simple Phase and Frequency Modulations. D. Goswami and W. S. Warren, Physical Review A 50(6), 5190–5196 (1994) [Abstract] [PDF] [BibTeX]

   Abstract: The effects of pulse shapes with simple phase and frequency modulation (phase proportional to amplitude or intensity, frequency proportional to intensity) are explored numerically. Many such shapes can be generated by combining self-phase-modulation with modern laser pulse-shaping capabilities (which are more flexible for amplitude modulation than for frequency modulation). Even though all of these wave forms begin and end at the same frequency (and hence violate the mathematical conditions for adiabatic inversion), we show that they can generate adiabatic population inversion or suppress intramolecular energy redistribution.

    BibTeX: @article{goswamiEffectsPulsesSimple1994,
     title = {Effects of Pulses with Simple Phase and Frequency Modulations},
     author = {Goswami, Debabrata and Warren, Warren S.},
     date = {1994-12-01},
     journaltitle = {Physical Review A},
     shortjournal = {Phys. Rev. A},
     volume = {50},
     number = {6},
     pages = {5190--5196},
     doi = {10/bnhs43},
     url = {https://link.aps.org/doi/10.1103/PhysRevA.50.5190},
     urldate = {2019-08-14}
   }
   

2. Femtosecond Laser Pulse Shaping by Use of Microsecond Radio-Frequency Pulses. C. W. Hillegas, J. X. Tull, D. Goswami, D. Strickland, and W. S. Warren, Optics Letters 19(10), 737–739 (1994) [Abstract] [PDF] [BibTeX]

   Abstract: We demonstrate a new pulse-shaping technique, using an acousto-optic modulator as a spatial modulator in a zero-dispersion delay line. Compared with existing techniques, this approach simplifies optical alignment and dramatically improves update rates. It should also improve flexibility for generating complex waveforms.

    BibTeX: @article{hillegasFemtosecondLaserPulse1994,
     title = {Femtosecond Laser Pulse Shaping by Use of Microsecond Radio-Frequency Pulses},
     author = {Hillegas, C. W. and Tull, J. X. and Goswami, D. and Strickland, D. and Warren, W. S.},
     date = {1994-05-15},
     journaltitle = {Optics Letters},
     shortjournal = {Opt. Lett., OL},
     volume = {19},
     number = {10},
     pages = {737--739},
     issn = {1539-4794},
     doi = {10/bgs6mn},
     url = {https://www.osapublishing.org/ol/abstract.cfm?uri=ol-19-10-737},
     urldate = {2019-08-14}
   }
   

3. Adiabatic Population Transfer with Frequency‐swept Laser Pulses. J. S. Melinger, S. R. Gandhi, A. Hariharan, D. Goswami, and W. S. Warren, The Journal of Chemical Physics 101(8), 6439–6454 (1994) [Abstract] [PDF] [BibTeX]

   Abstract: We present detailed experimental and theoretical results on population transfer with frequency‐swept picosecond laser pulses. Here, we demonstrate that intense frequency‐swept pulses, when applied in the adiabatic limit, lead to both more efficient and more selective excitation than do unmodulated laser pulses. The experimental work is performed on quasi‐two‐level systems (pentacene/p‐terphenyl crystal and Na vapor), quasi‐three‐level systems (Na vapor), and on more complex multilevel systems (I2 vapor). We discuss the different characteristics of adiabatic population transfer in both few‐level, and multilevel cases, and, in particular, present computer calculations to explore the effects of molecular rotations in multilevel adiabatic population transfer.

    BibTeX: @article{melingerAdiabaticPopulationTransfer1994,
     title = {Adiabatic Population Transfer with Frequency‐swept Laser Pulses},
     author = {Melinger, J. S. and Gandhi, Suketu R. and Hariharan, A. and Goswami, D. and Warren, W. S.},
     date = {1994-10-15},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {101},
     number = {8},
     pages = {6439--6454},
     issn = {0021-9606},
     doi = {10/dbhhsg},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.468368},
     urldate = {2019-08-14}
   }
   

1993

1. Control of Chemical Dynamics by Restricting Intramolecular Vibrational Relaxation. D. Goswami and W. S. Warren, The Journal of Chemical Physics 99(6), 4509–4517 (1993) [Abstract] [PDF] [BibTeX]

   Abstract: We address the issue of localization of bond energy in a molecule by stopping intramolecular vibrational relaxation (IVR). We show through model calculations that appropriate frequency sweeps permit selective locking over a well‐defined range of resonance frequencies, with little excitation outside that range. We also propose a modified version of an adiabatic half passage experiment that will perform photon locking without complications from inhomogeneities or partial excitation of other transitions for a bright state coupled to a finite number of dark states.

    BibTeX: @article{goswamiControlChemicalDynamics1993,
     title = {Control of Chemical Dynamics by Restricting Intramolecular Vibrational Relaxation},
     author = {Goswami, Debabrata and Warren, Warren S.},
     date = {1993-09-15},
     journaltitle = {The Journal of Chemical Physics},
     shortjournal = {J. Chem. Phys.},
     volume = {99},
     number = {6},
     pages = {4509--4517},
     issn = {0021-9606},
     doi = {10/bjh64b},
     url = {https://aip.scitation.org/doi/abs/10.1063/1.466050},
     urldate = {2019-08-14}
   }
   

1992

1. Laser-Enhanced NMR Spectroscopy. W. S. Warren, S. Mayr, D. Goswami, and A. P. West, Science 255(5052), 1683–1685 (1992) [Abstract] [PDF] [BibTeX]

   Abstract: Experimental studies show that optical irradiation far from any absorption bands can shift the resonances in a nuclear magnetic resonance (NMR) spectrum without significant heating. This effect may lead to increased dispersion in NMR studies of complex molecules.

    BibTeX: @article{warrenLaserenhancedNMRSpectroscopy1992,
     title = {Laser-Enhanced {{NMR}} Spectroscopy},
     author = {Warren, W. S. and Mayr, S. and Goswami, D. and West, A. P.},
     date = {1992-03-27},
     journaltitle = {Science},
     volume = {255},
     number = {5052},
     eprint = {1553555},
     eprinttype = {pmid},
     pages = {1683--1685},
     issn = {0036-8075, 1095-9203},
     doi = {10/fr8pjn},
     url = {https://science.sciencemag.org/content/255/5052/1683},
     urldate = {2019-08-14}
   }
   

1991

1. Fluorescence Quenching of Few Aromatic Amines by Chlorinated Methanes. D. Goswami, R. S. Sarpal, and S. K. Dogra, Bulletin of the Chemical Society of Japan 64(10), 3137–3141 (1991) [Abstract] [PDF] [BibTeX]

   Abstract: Fluorescence quenching of few aromatic amines; aniline (AB), 1-naphthylamine (1-AN), 2-naphthylamine (2-AN), 2,3-naphthalenediamine (2,3-DAN), 9-phenanthrenamine (9-AP), 1-pyrenamine (1-APy), 2-chrysenamine (2-AC), 6-chrysenamine (6-AC), and 3-fluoranthenamine (3-AF) by dichloromethane, chloroform, and carbon tetrachloride has been studied in cyclohexane and acetonitrile. The quenching rate constants (kq) have been determined in both the solvents and these values are nearly independent of the solvent polarity. The values of kq are nearly equal to diffusion-controlled limits (kdiff) for CHCl3 and CCl4 in both the solvents, whereas for CH2Cl2 it is three to four order of magnitude less than kdiff. For a given amine, kq increases with the increase in electron affinity of the quencher, whereas for a given quencher (dichloromethane) kq increases with the increase in singlet state energy of fluorophore. The results obtained are explained in terms of a quenching mechanism involving an intermediate donor–acceptor (DA)* complex formed between the excited aromatic amine and quencher.

    BibTeX: @article{goswamiFluorescenceQuenchingFew1991,
     title = {Fluorescence {{Quenching}} of {{Few Aromatic Amines}} by {{Chlorinated Methanes}}},
     author = {Goswami, Debabrata and Sarpal, Ranjit S. and Dogra, Sneh K.},
     date = {1991-10-01},
     journaltitle = {Bulletin of the Chemical Society of Japan},
     shortjournal = {BCSJ},
     volume = {64},
     number = {10},
     pages = {3137--3141},
     issn = {0009-2673},
     doi = {10/cd4jj6},
     url = {https://www.journal.csj.jp/doi/abs/10.1246/bcsj.64.3137},
     urldate = {2019-08-14}
   }
   

2. Colloidal Dispersions. W. B. Russel, W. B. Russel, D. A. Saville, and W. R. Schowalter, (Cambridge University Press, 1991) [Abstract] [BibTeX]

   Abstract: This book covers the physical side of colloidal science from the individual forces acting between particles smaller than a micrometer that are suspended in a liquid, through the resulting equilibrium and dynamic properties. A variety of internal forces both attractive and repulsive act in conjunction with Brownian motion and the balance between them all decides the phase behaviour. On top of this various external fields, such as gravity or electromagnetic fields, diffusion and non-Newtonian rheology produce complex effects, each of which is of important scientific and technological interest. The authors aim to impart a sound, quantitative understanding based on fundamental theory and experiments with well-characterised model systems. This broad grasp of the fundamentals lends insight and helps to develop the intuitive sense needed to isolate essential features of the technological problems and design critical experiments. The main prerequisites for understanding the book are basic fluid mechanics, statistical mechanics and electromagnetism, though self contained reviews of each subject are provided at appropriate points. Some facility with differential equations is also necessary. Exercises are included at the end of each chapter, making the work suitable as a textbook for graduate courses in chemical engineering or applied mathematics. It will also be useful as a reference for individuals in academia or industry undertaking research in colloid science.

    BibTeX: @book{russelColloidalDispersions1991,
     title = {Colloidal {{Dispersions}}},
     author = {Russel, William Bailey and Russel, W. B. and Saville, D. A. and Schowalter, W. R.},
     date = {1991},
     eprint = {3shp8Kl6YoUC},
     eprinttype = {googlebooks},
     publisher = {{Cambridge University Press}},
     isbn = {978-0-521-42600-8},
     pagetotal = {548}
   }