IIT Kanpur

Education / Work History

  • Optical Physicist, Forbes Marshall, Pune Bengaluru, Karnataka, India (present)
  • Scientist, General Electric, Bangalore (2016-2017)
  • Postdoc, University of California (2013-2015)
  • Postdoc, Stanford University (2010-2013)
  • Ph.D. Scholar, IIT Kanpur (2004-2009)
  • M.Sc., The American College (2000-2002)
  • B.Sc., Madhurai Kamaraj University (1996-1999)

Research Topic / Interest

Contact me to know my current interests.

Publications

These include only those published in our lab.

  1. 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, J. Phys. Chem. 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}}},
      volume = {113},
      issn = {1520-6106},
      url = {https://doi.org/10.1021/jp903753u},
      doi = {10/dc3b67},
      number = {51},
      journaltitle = {J. Phys. Chem. B},
      urldate = {2019-08-14},
      date = {2009-12-24},
      pages = {16332-16336},
      author = {Goswami, Tapas and Kumar, S. K. Karthick and Dutta, Aveek and Goswami, Debabrata}
    }
    
  2. 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},
      volume = {476},
      issn = {0009-2614},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409006666},
      doi = {10/fpmh7d},
      number = {1},
      journaltitle = {Chemical Physics Letters},
      urldate = {2019-08-14},
      date = {2009-07-07},
      pages = {31-36},
      author = {Karthick Kumar, S. K. and Tiwari, Vivek and Goswami, Tapas and Goswami, Debabrata}
    }
    
  3. 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},
      volume = {360},
      issn = {0301-0104},
      url = {http://www.sciencedirect.com/science/article/pii/S0301010409001219},
      doi = {10/b2h79c},
      number = {1},
      journaltitle = {Chemical Physics},
      urldate = {2019-08-14},
      date = {2009-06-12},
      pages = {47-52},
      author = {Goswami, Tapas and Karthick Kumar, S. K. and Dutta, Aveek and Goswami, Debabrata}
    }
    
  4. 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},
      volume = {96},
      issn = {0011-3891},
      url = {https://www.jstor.org/stable/24104778},
      number = {11},
      journaltitle = {Current Science},
      urldate = {2019-08-14},
      date = {2009},
      pages = {1496-1500},
      author = {Kumar, S. K. Karthick and Goswami, T. and Bhattacharyya, I. and Goswami, D.}
    }
    
  5. 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,
      langid = {english},
      title = {Time {{Comb Pulses Through Ultrafast Pulse Shaping}}},
      url = {https://www.osapublishing.org/abstract.cfm?uri=PR-2007-MB61},
      doi = {10/gf6c9f},
      eventtitle = {Photorefractive {{Effects}}, {{Photosensitivity}}, {{Fiber Gratings}}, {{Photonic Materials}} and {{More}}},
      booktitle = {Controlling {{Light}} with {{Light}}: {{Photorefractive Effects}}, {{Photosensitivity}}, {{Fiber Gratings}}, {{Photonic Materials}} and {{More}} (2007), Paper {{MB61}}},
      publisher = {{Optical Society of America}},
      urldate = {2019-08-14},
      date = {2007-10-14},
      pages = {MB61},
      author = {Kumar, S. K. Karthick and Goswami, D.}
    }
    
  6. 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},
      isbn = {978-981-270-379-8},
      url = {https://www.worldscientific.com/doi/abs/10.1142/9789812772510_0010},
      volumes = {0},
      booktitle = {Current {{Topics}} in {{Atomic}}, {{Molecular}} and {{Optical Physics}}},
      publisher = {{WORLD SCIENTIFIC}},
      urldate = {2019-08-14},
      date = {2006-12-01},
      pages = {133-141},
      author = {Karthick Kumar, S. K. and Goswami, Debabrata},
      doi = {10.1142/9789812772510_0010}
    }
    
  7. 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,
      langid = {english},
      title = {Femtosecond {{Spatio}}-{{Temporal Control}}},
      journaltitle = {International Conference on Optics and Photonics},
      date = {2009},
      pages = {4},
      author = {Goswami, Debabrata and Goswami, T and De, A K and Roy, D and Das, D and Kumar, S K Karthick}
    }
    
  8. 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},
      volume = {108},
      issn = {0011-3891},
      url = {https://www.jstor.org/stable/24905603},
      number = {10},
      journaltitle = {Current Science},
      urldate = {2019-08-01},
      date = {2015},
      pages = {1801-1803},
      author = {Kumar, Ajitesh and Kumar, S. K. Karthick and Singhal, Sumit and Goswami, Debabrata}
    }
    
  9. Spectrally Resolved Photon-Echo Spectroscopy of Rhodamine-6G. A. Kumar, S. K. Karthick, and D. Goswami, J Spectrosc Dyn 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}}},
      volume = {3},
      issn = {2249-2704},
      url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790070/},
      number = {1},
      journaltitle = {J Spectrosc Dyn},
      urldate = {2019-08-02},
      date = {2013-02},
      pages = {2},
      author = {Kumar, Ajitesh and Karthick, S. K. and Goswami, D.},
      eprinttype = {pmid},
      eprint = {24098869},
      pmcid = {PMC3790070}
    }
    
  10. Chirp and Polarization Control of Femtosecond Molecular Fragmentation. T. Goswami, D. K. Das, S. K. Karthick Kumar, and D. Goswami, Indian J Phys 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,
      langid = {english},
      title = {Chirp and Polarization Control of Femtosecond Molecular Fragmentation},
      volume = {86},
      issn = {0974-9845},
      url = {https://my.pcloud.com/publink/show?code=XZXvxr7ZAeDqROTwM5f4IAxCCHc87VQw2hJ7},
      doi = {10/f3xs5c},
      number = {3},
      journaltitle = {Indian J Phys},
      urldate = {2019-08-02},
      date = {2012-03-01},
      pages = {181-185},
      author = {Goswami, T. and Das, D. K. and Karthick Kumar, S. K. and Goswami, D.}
    }
    
  11. 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}}},
      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.}
    }
    
  12. 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},
      volume = {8173},
      url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8173/817325/Spectrally-resolved-femtosecond-photon-echo-spectroscopy-of-astaxanthin/10.1117/12.899781.short},
      doi = {10/fs3jxj},
      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 = {2019-08-02},
      date = {2011-08-23},
      pages = {817325},
      author = {Kumar, Ajitesh and Kumar, S. K. Karthick and Gupta, Aditya and Goswami, Debabrata}
    }
    
  13. 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, J. Phys. Chem. 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{goswamiProbingUltrafastSolution2010,
      title = {Probing the {{Ultrafast Solution Dynamics}} of a {{Cyanine Dye}} in an {{Organic Solvent Interfaced}} with {{Water}}},
      volume = {113},
      issn = {1520-6106},
      url = {https://doi.org/10.1021/jp903753u},
      doi = {10/dc3b67},
      number = {51},
      journaltitle = {J. Phys. Chem. B},
      urldate = {2019-08-14},
      date = {2009-12-24},
      pages = {16332-16336},
      author = {Goswami, Tapas and Kumar, S. K. Karthick and Dutta, Aveek and Goswami, Debabrata}
    }
    
  14. 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{karthickkumarSpectrallyResolvedPhoton2010,
      title = {Spectrally Resolved Photon Echo Spectroscopy of {{Zn}}({{II}}), {{Co}}({{II}}) and {{Ni}}({{II}})–Octaethyl Porphyrins},
      volume = {476},
      issn = {0009-2614},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409006666},
      doi = {10/fpmh7d},
      number = {1},
      journaltitle = {Chemical Physics Letters},
      urldate = {2019-08-14},
      date = {2009-07-07},
      pages = {31-36},
      author = {Karthick Kumar, S. K. and Tiwari, Vivek and Goswami, Tapas and Goswami, Debabrata}
    }
    
  15. 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{goswamiControlLaserInduced2010,
      title = {Control of Laser Induced Molecular Fragmentation of N-Propyl Benzene Using Chirped Femtosecond Laser Pulses},
      volume = {360},
      issn = {0301-0104},
      url = {http://www.sciencedirect.com/science/article/pii/S0301010409001219},
      doi = {10/b2h79c},
      number = {1},
      journaltitle = {Chemical Physics},
      urldate = {2019-08-14},
      date = {2009-06-12},
      pages = {47-52},
      author = {Goswami, Tapas and Karthick Kumar, S. K. and Dutta, Aveek and Goswami, Debabrata}
    }
    
  16. 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{kumarVisible20femtosecondPulse2010,
      title = {Visible 20-Femtosecond Pulse Generation by Double-Pass Non-Collinear Optical Parametric Amplifier},
      volume = {96},
      issn = {0011-3891},
      url = {https://www.jstor.org/stable/24104778},
      number = {11},
      journaltitle = {Current Science},
      urldate = {2019-08-14},
      date = {2009},
      pages = {1496-1500},
      author = {Kumar, S. K. Karthick and Goswami, T. and Bhattacharyya, I. and Goswami, D.}
    }
    
  17. 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{goswamiFemtosecondSpatioTemporalControl2010,
      langid = {english},
      title = {Femtosecond {{Spatio}}-{{Temporal Control}}},
      journaltitle = {International Conference on Optics and Photonics},
      date = {2009},
      pages = {4},
      author = {Goswami, Debabrata and Goswami, T and De, A K and Roy, D and Das, D and Kumar, S K Karthick}
    }
    
  18. 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{goswamiChirpPolarizationControl2013,
      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},
      pages = {181--185},
      issn = {0974-9845},
      doi = {10/f3xs5c},
      url = {https://my.pcloud.com/publink/show?code=XZXvxr7ZAeDqROTwM5f4IAxCCHc87VQw2hJ7},
      urldate = {2019-08-02},
      keywords = {_tablet,42.25.Ja,42.50.Hz,42.62.Fi,42.65.Re,Chirp pulses,Control,Femtochemistry,Photodissociation},
      langid = {english},
      number = {3}
    }
    
  19. 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{goswamiControlLaserInduced2011,
      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},
      pages = {47--52},
      issn = {0301-0104},
      doi = {10/b2h79c},
      url = {http://www.sciencedirect.com/science/article/pii/S0301010409001219},
      urldate = {2019-08-14},
      keywords = {_tablet,Chirped femtosecond laser pulse,Coherent control,Fragmentation},
      number = {1}
    }
    
  20. 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{goswamiFemtosecondSpatioTemporalControl2011,
      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},
      keywords = {_tablet,⛔ No DOI found},
      langid = {english}
    }
    
  21. 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{goswamiProbingUltrafastSolution2011,
      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},
      pages = {16332--16336},
      issn = {1520-6106},
      doi = {10/dc3b67},
      url = {https://doi.org/10.1021/jp903753u},
      urldate = {2019-08-14},
      keywords = {_tablet},
      number = {51}
    }
    
  22. 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}}},
      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},
      pages = {251--253},
      issn = {0094-243X},
      doi = {10/bfnp4m},
      url = {https://aip.scitation.org/doi/abs/10.1063/1.3635869},
      urldate = {2019-08-02},
      keywords = {_tablet},
      number = {1}
    }
    
  23. 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{karthickkumarSpectrallyResolvedPhoton2011,
      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},
      pages = {31--36},
      issn = {0009-2614},
      doi = {10/fpmh7d},
      url = {http://www.sciencedirect.com/science/article/pii/S0009261409006666},
      urldate = {2019-08-14},
      keywords = {_tablet},
      number = {1}
    }
    
  24. 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{karthickkumarUltrafastPulseShaping2007,
      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},
      keywords = {_tablet},
      volumes = {0}
    }
    
  25. 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{kumarSpectrallyResolvedFemtosecond2012,
      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}}},
      keywords = {_tablet}
    }
    
  26. 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{kumarSpectrallyResolvedPhotonecho2014,
      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},
      pages = {2},
      issn = {2249-2704},
      url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790070/},
      urldate = {2019-08-02},
      eprint = {24098869},
      eprinttype = {pmid},
      keywords = {_tablet},
      number = {1},
      pmcid = {PMC3790070}
    }
    
  27. 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] [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{kumarStudyTwoXanthene2016,
      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},
      pages = {1801--1803},
      issn = {0011-3891},
      eprint = {24905603},
      eprinttype = {jstor},
      keywords = {_tablet},
      number = {10}
    }
    
  28. 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{kumarTimeCombPulses2008,
      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}}},
      keywords = {_tablet,Erbium fibers,Femtosecond fiber lasers,Femtosecond pulses,Fourier transforms,Phase modulation,Pulse shaping},
      langid = {english}
    }
    
  29. 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] [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{kumarVisible20femtosecondPulse2011,
      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},
      pages = {1496--1500},
      issn = {0011-3891},
      eprint = {24104778},
      eprinttype = {jstor},
      keywords = {_tablet},
      number = {11}
    }