Amit Nag

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Education / Work History

• Assistant Professor, BITS Pilani, Hyderabad Campus, India (2012–present)
• Post-doctoral researcher, LMU, Munich, Germany (2011 - 2012)
• Post-doctoral researcher, University of California, Irvine, CA, USA (2009-2011)
• Post-doctoral researcher, Princeton University, Princeton, NJ, USA (Fall 2009)
• Ph.D., Scholar, IIT Kanpur (2009)
• M.Sc., Jadavpur University, Kolkata, W.B., India (2003)
• B.Sc., Burdwan Raj College,University of Burdwan, Burdwan, W.B., India (2001)

Thesis Abstract

Accurate Quantification and Control of Two-Photon Processes

The main theme of the thesis is to understand the two-photon process, its accurate quantification and control using femtosecond pulsed lasers. This effort culminated in identifying control parameters. The thesis has been organized into seven chapters. The introductory Chapter 1 starts with the brief history of the two-photon absorption (TPA) process, basic concepts and its significant applications in different areas of science. A general importance of the TPA related studies and a brief review of these studies performed by other research groups have been presented. In Chapter 2, the principles, technical details of different experimental setups to measure the TPA process and different pulse characterization techniques are described in detail. Chapter 3 of the thesis describes sensitive measurements of large TPA cross-section (TPCS) values of different chromophores starting from modified porphyrin to simple co-ordination metal complexes using open aperture z-scan method with high repetition rate (HRR) MHz lasers. Very small nonlinearities of neat solvent molecules are also described. The pulse pileup problems and cumulative thermal effects are the major difficulties to apprehend in the experiments using HRR lasers. In Chapter 4, it has been shown that an optical chopper can be optimized to sufficiently minimize the thermal contributions of HRR lasers by periodic blanking of the laser pulses to the system under study. This particular study also unifies the TPCS measurements from z-scan and two-photon fluorescence (TPF) techniques. In Chapter 5, experimental observations are presented on how solvents can vary the TPA and TPF properties of fluorescent dyes. Chapter 6 presents an interesting study of modulation of TPF through variation of the incident laser polarization for different fluorescent dyes. In Chapter 7, the design of a folded geometry acousto-optic modulator based pulse shaper is discussed, which is capable of shaping individual pulses from a kHz amplified laser. Once the pulse shaping scheme is established and characterized, we experimentally study the variation of TPA and TPF for several chromophores in solutions by simple phase ordering a femtosecond laser pulse.

Research Topic / Interest

Contact me to know my current interests.

Publications

These include only those published in our lab.

1. 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}}}
   }
   

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. 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}
   }
   

4. 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}
   }
   

5. 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}
   }
   

6. 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}
   }
   

7. 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}
   }
   

8. 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}
   }
   

9. 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}
   }
   

10. 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}
    }
    

11. 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{dasSolventEffectMultiple2019,
      title = {Solvent Effect on Multiple Emission and Ultrafast Dynamics of Higher Excited States},
      volume = {706},
      issn = {0009-2614},
      url = {https://my.pcloud.com/publink/show?code=XZOAxr7ZeXIX0Ahn0DBrmUdo3wS0tyDPhbz7},
      doi = {10/gd3phb},
      journaltitle = {Chemical Physics Letters},
      urldate = {2019-08-01},
      date = {2018-08-16},
      pages = {375-379},
      author = {Das, Dipak Kumar and Makhal, Krishnandu and Goswami, Debabrata}
    }
    

12. 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{goswamiSolventEffectDual2019,
      langid = {english},
      location = {{Cham}},
      title = {Solvent {{Effect}} on {{Dual Fluorescence}} and the {{Corresponding Excited State Dynamics}}},
      isbn = {978-3-030-01569-5},
      url = {https://doi.org/10.1007/978-3-030-01569-5_7},
      booktitle = {Reviews in {{Fluorescence}} 2017},
      series = {Reviews in {{Fluorescence}}},
      publisher = {{Springer International Publishing}},
      urldate = {2019-08-01},
      date = {2018},
      pages = {145-160},
      author = {Goswami, Debabrata and Das, Dipak Kumar and Makhal, Krishnandu},
      editor = {Geddes, Chris D.},
      doi = {10.1007/978-3-030-01569-5_7}
    }
    

13. 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, J Fluoresc 28(3), 855–862 (2018) [PDF] [BibTeX]

     BibTeX: @article{dasTwoPhotonSpectroscopy2019,
      langid = {english},
      title = {Two {{Photon Spectroscopy Can Serve}} as a {{Marker}} of {{Protein Denaturation Pathway}}},
      volume = {28},
      issn = {1053-0509, 1573-4994},
      url = {https://my.pcloud.com/publink/show?code=XZGNxr7ZDvT2qqOXdaJrTjbB8A2tB5nJ8kH7},
      doi = {10.1007/s10895-018-2250-3},
      number = {3},
      journaltitle = {J Fluoresc},
      urldate = {2019-08-01},
      date = {2018-05},
      pages = {855-862},
      author = {Das, Dipak Kumar and Islam, Sk Imadul and Samanta, Nirnay and Yadav, Yogendra and Goswami, Debabrata and Mitra, Rajib Kumar}
    }
    

14. 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{dasObservingGroundState2019,
      langid = {english},
      title = {Observing Ground State Vibrational Coherence and Excited State Relaxation Dynamics of a Cyanine Dye in Pure Solvents},
      volume = {20},
      url = {https://my.pcloud.com/publink/show?code=XZ1Axr7ZxiTGNbfEV1bmLPqho9PtQzSq3qUk},
      doi = {10/gf5mqz},
      number = {19},
      journaltitle = {Physical Chemistry Chemical Physics},
      urldate = {2019-08-01},
      date = {2018},
      pages = {13400-13411},
      author = {Das, Dipak Kumar and Makhal, Krishnandu and Goswami, Debabrata}
    }
    

15. 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{dasDirectObservationCoherent2015,
      langid = {english},
      title = {Direct {{Observation}} of {{Coherent Oscillations}} in {{Solution}} Due to {{Microheterogeneous Environment}}},
      volume = {4},
      issn = {2045-2322},
      url = {https://www.nature.com/articles/srep06097},
      doi = {10/gf5mth},
      journaltitle = {Scientific Reports},
      urldate = {2019-08-01},
      date = {2014-08-18},
      pages = {6097},
      author = {Das, Dipak Kumar and Makhal, Krishnandu and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata}
    }
    

16. 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{goswamiControllingFemtosecondLaserdriven2014,
      title = {Controlling the Femtosecond Laser-Driven Transformation of Dicyclopentadiene into Cyclopentadiene},
      volume = {558},
      issn = {0009-2614},
      url = {https://my.pcloud.com/publink/show?code=XZFvxr7ZpduyXffXsJj4NXDLmSt1zLjBhELV},
      doi = {10/f4nnb2},
      journaltitle = {Chemical Physics Letters},
      urldate = {2019-08-02},
      date = {2013-02-12},
      pages = {1-7},
      author = {Goswami, Tapas and Das, Dipak K. and Goswami, Debabrata}
    }
    

17. 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{goswamiUsingMolecularStates2012,
      title = {Towards {{Using Molecular States}} as {{Qubits}}},
      volume = {1384},
      issn = {0094-243X},
      url = {https://aip.scitation.org/doi/abs/10.1063/1.3635869},
      doi = {10/bfnp4m},
      number = {1},
      journaltitle = {AIP Conference Proceedings},
      urldate = {2019-08-02},
      date = {2011-09-23},
      pages = {251-253},
      author = {Goswami, Debabrata and Goswami, Tapas and Kumar, S. K. Karthick and Das, Dipak K.}
    }
    

18. 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{dasControlFemtosecondLaser2012,
      title = {Control of Femtosecond Laser Driven Retro-{{Diels}}-{{Alder}}-like Reaction of Dicyclopentadiene},
      volume = {8173},
      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},
      doi = {10/dsc8s7},
      eventtitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      booktitle = {Photonics 2010: {{Tenth International Conference}} on {{Fiber Optics}} and {{Photonics}}},
      publisher = {{International Society for Optics and Photonics}},
      urldate = {2019-08-13},
      date = {2011-08-23},
      pages = {81730O},
      author = {Das, Dipak Kumar and Goswami, Tapas and Goswami, Debabrata}
    }
    

19. Towards Using Molecular Ions as Qubits: Femtosecond Control of Molecular Fragmentation with Multiple Knobs. T. Goswami, D. K. Das, and D. Goswami, Pramana - J Phys 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{goswamiUsingMolecularIons2011,
      langid = {english},
      title = {Towards Using Molecular Ions as Qubits: {{Femtosecond}} Control of Molecular Fragmentation with Multiple Knobs},
      volume = {75},
      issn = {0973-7111},
      url = {https://doi.org/10.1007/s12043-010-0190-9},
      doi = {10.1007/s12043-010-0190-9},
      shorttitle = {Towards Using Molecular Ions as Qubits},
      number = {6},
      journaltitle = {Pramana - J Phys},
      urldate = {2019-08-14},
      date = {2010-12-01},
      pages = {1065-1069},
      author = {Goswami, Tapas and Das, Dipak K. and Goswami, Debabrata}
    }