FemtoLab: Arijit De

Arijit De

Education / Work History

Assistant Professor, Department of Chemical Sciences, IISER Mohali (2014-present)
Postdoc, Physical Biosciences Division, Lawrence Berkeley National Laboratory and Dept. of Chemistry, University of California Berkeley (2010-2014)
- Advisor: Prof. Graham R. Fleming
Senior Project Scientist, Department of Chemistry, IIT Kanpur (2010)
- Advisor: Prof. Debabrata Goswami
Ph.D., Department of Chemistry, IIT Kanpur (2010)
- Advisor: Prof. Debabrata Goswami
- Thesis: Spatio-temporal control in laser-scanning fluorescence microscopy and optical trapping
M.Sc., Department of Chemistry, IIT Kanpur (2005)
- Project: Ultrafast pulse shaping

Thesis Abstract

Spatio-temporal control in laser-scanning fluorescence microscopy and optical trapping

This thesis describes the development of several advanced fluorescence imaging methods and addresses few technical developments of a laser tweezer. The work presented in this thesis has taken the concept of dynamical control to new vistas and thrown insight on spatiotemporal dynamical control with applications in fluorescence microscopy and optical trapping through experimental demonstrations. Further studies in this exciting field are expected to enrich our understanding in condensed phase molecular dynamics at the single molecule level. The thesis starts with a prelude (Chapter 0) considering the chronological development in the science of microscopy as well as of optical trapping. Chapter 1 deals with the motivation behind the present work with discussion addressing the open problems left to be solved regarding dynamics and control in fluorescence microscopy and optical trapping. Chapter 2 discusses the instrumentation part in detail. Chapter 3 discusses the optimal choice of one-photon pulsed illumination (instead of conventional continuous wave illumination) suitable to have significantly enhanced fluorescence. Towards the end of this chapter, the built-in confocality under ultrafast pulsed illumination is addressed. In Chapter 4, the mechanism of laser-induced photo-thermal corruption due to pulse pile-up effect is discussed. In Chapter 5, a detail discussion on molecular structure-property correlation regarding two-photon absorption cross-section is given with a discussion on the measurement of the cross-section values. Chapter 6 discusses how precise time delay between pair of ultrafast pulses can lead to possible selective excitation in fluorescence microscopy by making use of both the coherent vibrational wave-packet interferometry as well as by the selective fluorescence suppression by stimulated emission. In Chapter 7, besides a discussion on a simple method of force calibration in optical tweezer by using pulse-train modulation, the use of gigantic peak-power of a femto-second laser pulse (with rather low average power) leading to stable optical trap of latex nano-particles is demonstrated, which is otherwise impossible with continuous wave excitation at the same average power. The concluding chapter, Chapter 8, summarizes the possibility of having full control over all degrees of freedom, namely translational, rotational, vibrational and electronic, by combining laser pulse-shaping with laser beam-shaping.

Publications

These include only those published in our lab.

Journal Papers

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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
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}
}
```
Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De and D. Goswami, JBO 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{deUltrafastPulsepairControl2010,
  title = {Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
  volume = {14},
  issn = {1083-3668, 1560-2281},
  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},
  doi = {10/fvc8h7},
  number = {6},
  journaltitle = {JBO},
  urldate = {2019-08-14},
  date = {2009-11},
  pages = {064018},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination. A. K. De, D. Roy, A. Dutta, and D. Goswami, Appl. Opt., AO 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{deStableOpticalTrapping2010,
  langid = {english},
  title = {Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination},
  volume = {48},
  issn = {2155-3165},
  url = {https://www.osapublishing.org/ao/abstract.cfm?uri=ao-48-31-G33},
  doi = {10/b9sxj4},
  number = {31},
  journaltitle = {Appl. Opt., AO},
  urldate = {2019-08-14},
  date = {2009-11-01},
  pages = {G33-G37},
  author = {De, Arijit Kumar and Roy, Debjit and Dutta, Aveek and Goswami, Debabrata}
}
```
A Systematic Study on Fluorescence Enhancement under Single-Photon Pulsed Illumination. A. K. De and D. Goswami, J Fluoresc 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{deSystematicStudyFluorescence2010,
  langid = {english},
  title = {A {{Systematic Study}} on {{Fluorescence Enhancement}} under {{Single}}-Photon {{Pulsed Illumination}}},
  volume = {19},
  issn = {1573-4994},
  url = {https://doi.org/10.1007/s10895-009-0489-4},
  doi = {10/bk2648},
  number = {5},
  journaltitle = {J Fluoresc},
  urldate = {2019-08-14},
  date = {2009-09-01},
  pages = {931-937},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
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{deSimpleTwistSignal2010,
  langid = {english},
  title = {A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy},
  volume = {235},
  issn = {1365-2818},
  url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03176.x},
  doi = {10/ckpt72},
  number = {2},
  journaltitle = {Journal of Microscopy},
  urldate = {2019-08-14},
  date = {2009},
  pages = {119-123},
  author = {De, A. K. and Goswami, D.}
}
```
Exploring the Nature of Photo-Damage in Two-Photon Excitation by Fluorescence Intensity Modulation. A. K. De and D. Goswami, J Fluoresc 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{deExploringNaturePhotoDamage2009,
  langid = {english},
  title = {Exploring the {{Nature}} of {{Photo}}-{{Damage}} in {{Two}}-Photon {{Excitation}} by {{Fluorescence Intensity Modulation}}},
  volume = {19},
  issn = {1573-4994},
  url = {https://doi.org/10.1007/s10895-008-0405-3},
  doi = {10/ck4wnn},
  number = {2},
  journaltitle = {J Fluoresc},
  urldate = {2019-08-14},
  date = {2008-08-21},
  pages = {381},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
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{deAddingNewDimensions2010,
  langid = {english},
  title = {Adding New Dimensions to Laser-Scanning Fluorescence Microscopy},
  volume = {233},
  issn = {1365-2818},
  url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03122.x},
  doi = {10/fd3jh9},
  number = {2},
  journaltitle = {Journal of Microscopy},
  urldate = {2019-08-14},
  date = {2009},
  pages = {320-325},
  author = {De, A. K. and Goswami, D.}
}
```
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{deTwophotonFluorescenceDiagnostics2012,
  langid = {english},
  title = {Two-Photon Fluorescence Diagnostics of Femtosecond Laser Tweezers},
  volume = {101},
  url = {https://my.pcloud.com/publink/show?code=XZyaxr7ZQuCnGQH0PFBeRMoMq6mRURASwEJk},
  number = {7},
  journaltitle = {CURRENT SCIENCE},
  date = {2011},
  pages = {4},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata}
}
```
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, JBO 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{deSelectiveTwophotonFluorescence2012,
  title = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation: Control by Selective One-Color Stimulated Emission},
  volume = {16},
  issn = {1083-3668, 1560-2281},
  url = {https://my.pcloud.com/publink/show?code=XZoNxr7Zgv99AAhjLt4lAwzfutsBwYsdJNvy},
  doi = {10/fqkzpp},
  shorttitle = {Selective Two-Photon Fluorescence Suppression by Ultrafast Pulse-Pair Excitation},
  number = {10},
  journaltitle = {JBO},
  urldate = {2019-08-02},
  date = {2011-10},
  pages = {100505},
  author = {De, Arijit K. and Roy, Debjit and Goswami, Debabrata}
}
```
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{deControllingMolecularMotions2012,
  title = {Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping: A Spatiotemporal Approach},
  volume = {30},
  issn = {0144-235X},
  url = {https://doi.org/10.1080/0144235X.2011.603237},
  doi = {10/fmhbzc},
  shorttitle = {Towards Controlling Molecular Motions in Fluorescence Microscopy and Optical Trapping},
  number = {3},
  journaltitle = {International Reviews in Physical Chemistry},
  urldate = {2019-08-13},
  date = {2011-07-01},
  pages = {275-299},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy. A. K. De, D. Roy, and D. Goswami, Phys. Rev. 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{deFluorophoreDiscriminationTracing2012,
  title = {Fluorophore Discrimination by Tracing Quantum Interference in Fluorescence Microscopy},
  volume = {83},
  url = {https://link.aps.org/doi/10.1103/PhysRevA.83.015402},
  doi = {10/c73nhs},
  number = {1},
  journaltitle = {Phys. Rev. A},
  urldate = {2019-08-14},
  date = {2011-01-21},
  pages = {015402},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata}
}
```
Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation. A. K. De, D. Roy, and D. Goswami, JBO 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{deSelectiveSuppressionTwophoton2011,
  title = {Selective Suppression of Two-Photon Fluorescence in Laser Scanning Microscopy by Ultrafast Pulse-Train Excitation},
  volume = {15},
  issn = {1083-3668, 1560-2281},
  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},
  doi = {10/cp9rx2},
  number = {6},
  journaltitle = {JBO},
  urldate = {2019-08-14},
  date = {2010-11},
  pages = {060502},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata}
}
```
Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy. A. K. De and D. Goswami, JBO 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{deUltrafastPulsepairControl2011,
  title = {Ultrafast Pulse-Pair Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
  volume = {14},
  issn = {1083-3668, 1560-2281},
  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},
  doi = {10/fvc8h7},
  number = {6},
  journaltitle = {JBO},
  urldate = {2019-08-14},
  date = {2009-11},
  pages = {064018},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination. A. K. De, D. Roy, A. Dutta, and D. Goswami, Appl. Opt., AO 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{deStableOpticalTrapping2011,
  langid = {english},
  title = {Stable Optical Trapping of Latex Nanoparticles with Ultrashort Pulsed Illumination},
  volume = {48},
  issn = {2155-3165},
  url = {https://www.osapublishing.org/ao/abstract.cfm?uri=ao-48-31-G33},
  doi = {10/b9sxj4},
  number = {31},
  journaltitle = {Appl. Opt., AO},
  urldate = {2019-08-14},
  date = {2009-11-01},
  pages = {G33-G37},
  author = {De, Arijit Kumar and Roy, Debjit and Dutta, Aveek and Goswami, Debabrata}
}
```
A Systematic Study on Fluorescence Enhancement under Single-Photon Pulsed Illumination. A. K. De and D. Goswami, J Fluoresc 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{deSystematicStudyFluorescence2011,
  langid = {english},
  title = {A {{Systematic Study}} on {{Fluorescence Enhancement}} under {{Single}}-Photon {{Pulsed Illumination}}},
  volume = {19},
  issn = {1573-4994},
  url = {https://doi.org/10.1007/s10895-009-0489-4},
  doi = {10/bk2648},
  number = {5},
  journaltitle = {J Fluoresc},
  urldate = {2019-08-14},
  date = {2009-09-01},
  pages = {931-937},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
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{deSimpleTwistSignal2011,
  langid = {english},
  title = {A Simple Twist for Signal Enhancement in Non-Linear Optical Microscopy},
  volume = {235},
  issn = {1365-2818},
  url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03176.x},
  doi = {10/ckpt72},
  number = {2},
  journaltitle = {Journal of Microscopy},
  urldate = {2019-08-14},
  date = {2009},
  pages = {119-123},
  author = {De, A. K. and Goswami, D.}
}
```
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{deAddingNewDimensions2011,
  langid = {english},
  title = {Adding New Dimensions to Laser-Scanning Fluorescence Microscopy},
  volume = {233},
  issn = {1365-2818},
  url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2818.2009.03122.x},
  doi = {10/fd3jh9},
  number = {2},
  journaltitle = {Journal of Microscopy},
  urldate = {2019-08-14},
  date = {2009},
  pages = {320-325},
  author = {De, A. K. and Goswami, D.}
}
```

Conference Proceedings

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}}}
}
```
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}}}
}
```
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}}}
}
```
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}
}
```
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{deThreedimensionalImageFormation2010,
  title = {Three-Dimensional Image Formation under Single-Photon Ultra-Short Pulsed Illumination},
  volume = {7378},
  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},
  doi = {10/b7mtnv},
  eventtitle = {Scanning {{Microscopy}} 2009},
  booktitle = {Scanning {{Microscopy}} 2009},
  publisher = {{International Society for Optics and Photonics}},
  urldate = {2019-08-14},
  date = {2009-05-22},
  pages = {737827},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
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{deCoherentControlMultiphoton2010,
  title = {Coherent Control in Multiphoton Fluorescence Imaging},
  volume = {7183},
  url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7183/71832B/Coherent-control-in-multiphoton-fluorescence-imaging/10.1117/12.807687.short},
  doi = {10/d2cztk},
  eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}},
  booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}},
  publisher = {{International Society for Optics and Photonics}},
  urldate = {2019-08-14},
  date = {2009-02-25},
  pages = {71832B},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
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{deStableTrappingSingle2011,
  title = {Towards Stable Trapping of Single Macromolecules in Solution},
  volume = {7762},
  url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7762/776203/Towards-stable-trapping-of-single-macromolecules-in-solution/10.1117/12.862364.short},
  doi = {10/ckqvtz},
  eventtitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}},
  booktitle = {Optical {{Trapping}} and {{Optical Micromanipulation VII}}},
  publisher = {{International Society for Optics and Photonics}},
  urldate = {2019-08-14},
  date = {2010-08-27},
  pages = {776203},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata}
}
```
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{deSpatiotemporalControlMultiphoton2011,
  title = {Spatio-Temporal Control in Multiphoton Fluorescence Laser-Scanning Microscopy},
  volume = {7569},
  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},
  doi = {10/c529hw},
  eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}},
  booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences X}}},
  publisher = {{International Society for Optics and Photonics}},
  urldate = {2019-08-14},
  date = {2010-02-26},
  pages = {756929},
  author = {De, Arijit Kumar and Roy, Debjit and Goswami, Debabrata}
}
```
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{deThreedimensionalImageFormation2011,
  title = {Three-Dimensional Image Formation under Single-Photon Ultra-Short Pulsed Illumination},
  volume = {7378},
  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},
  doi = {10/b7mtnv},
  eventtitle = {Scanning {{Microscopy}} 2009},
  booktitle = {Scanning {{Microscopy}} 2009},
  publisher = {{International Society for Optics and Photonics}},
  urldate = {2019-08-14},
  date = {2009-05-22},
  pages = {737827},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```
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{deCoherentControlMultiphoton2011,
  title = {Coherent Control in Multiphoton Fluorescence Imaging},
  volume = {7183},
  url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/7183/71832B/Coherent-control-in-multiphoton-fluorescence-imaging/10.1117/12.807687.short},
  doi = {10/d2cztk},
  eventtitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}},
  booktitle = {Multiphoton {{Microscopy}} in the {{Biomedical Sciences IX}}},
  publisher = {{International Society for Optics and Photonics}},
  urldate = {2019-08-14},
  date = {2009-02-25},
  pages = {71832B},
  author = {De, Arijit Kumar and Goswami, Debabrata}
}
```

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Thermal Effects and Sensing

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Arijit De

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Spatio-temporal control in laser-scanning fluorescence microscopy and optical trapping

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