Ajitesh Kumar

Education / Work History

• ONGC (present)
• Ph.D. Scholar, IIT Kanpur (2015)

Thesis Abstract

Probing Molecular Dynamics in Condensed Phase by Spectrally Resolved Photon Echo Spectroscopy

My thesis uses a multidimensional technique, Spectrally Resolved Photon Echo Spectroscopy (SRPE) to study the vibrational and electronic dynamics in complex molecular systems. The thesis also details out the theory and construction of a three pulse photon echo experimental setup. This also provides an overview and background of SRPE spectroscopy and discusses our femtosecond SRPE experimental system. The entire experimental setup, including the ultrafast laser systems is also describe. The functioning of home built femtosecond oscillator and Multipass amplifier (ODIN) has been described in details. The ODIN is pumped by a Nd:YAG laser (Evolution-15, Coherent Inc.) that generates nanosecond pulses at 532 nm wavelength and has a repetition rate of 1 KHz. The seed pulses for the ODIN comes from the home-built Ti:Sapphire oscillator (KM–Labs kit). The optical parametric amplifier, TOPAS (Quantronix Inc.) generates tunable laser pulses that cover the whole visible spectral region. We also describe the second laser system, which consists of a tunable repetition rate commercial Regenerative Amplifier (Spitfire Pro, Spectra Physics). This amplifier is seeded by femtosecond pulses from a 82 MHz Ti:Sapphire oscillator (Mai Tai, Spectra Physics) and amplified by a Nd:YLF Pump laser system (Empower, Spectra Physics). The technique used to measure the pulses coming out of these lasers is also described. Spectrally Resolved Photon Echo spectroscopy (SRPE) of Astaxanthin in two different solvents by using amplified laser system is discussed. This technique is also used to study the Rhodamine 6G (Rh6G) dye at two different excitation wavelengths. The study of Zinc substitution effect on the molecular dynamics of Protoporphyrin-IX in dichloromethane solvent is also presented by SRPE technique. This technique is further used in off-resonance condition for the first time to study the coherence and population dynamics of CdSe quantum-dots. The comparative study of the molecular dynamics of two xanthene dye derivatives (Rhodamine 6G and Fluorescein 548) is presented by using the SRPE spectroscopy.

Research Topic / Interest

Contact me to know my current interests.

Publications

These include only those published in our lab.

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

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

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

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

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

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

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

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

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

4. 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{kumarStudyTwoXanthene2016,
     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}
   }
   

5. 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{kumarSpectrallyResolvedPhotonecho2014,
     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}
   }
   

6. 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},
     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}
   }