Tushar Gaur

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Education / Work History

• Ph.D., IISc Bangalore
• M.Tech, Center for Lasers and Photonics (CELP), IIT Kanpur (2017-2019)
• B.Tech, Rajasthan Technical University (2009-2013)

Thesis Abstract

Discerning the Effects of Thermal Nonlinearity in Optical Trapping

The field of Optical Trapping is almost in the end of its fifth decade, importance of thermal effects have been addressed but no significant work was done in calculating the thermal effects on force and potential of the trapped particle. With the advent of using ultra short pulses in trapping it became important to describe the thermal effects on optical trapping to differentiate and articulate the advantages of pulsed lasers over CW laser based trapping. A proper theoretical comparison for the rise in temperature for both CW laser and Pulsed laser was done but the model worked only uptil pulse width of a few nanoseconds as we move to the subpico second pulses theoretical model cannot be used to predict the temperature due to computational limitations. As predicting the temperature in water medium for the case of femtosecond pulses was not approachable computationally, some other technique needed to be developed. To narrow down the gap between theoretical model and experiments it is important that the technique to be used includes all the thermal effects in optical trapping so, thermal nonlinearity of medium was included in the force equations of trapped particle. For this to happen Z-scan technique was used to measure the thermal nonlinear coefficients of various solution with both pulsed laser and CW laser which were then incorporated in optical trapping force equations through a newly generated MATLAB code to find out the effects of thermal nonlinearity which is directly related to rise in temperature of medium for studying the thermal effects on optical trapping. Results clearly show significant effects on forces and potential for trapped particle on adding thermal nonlinearity, a comparison was made to establish the difference in trapping when we use a pulsed laser and CW laser for two different regimes Rayleigh and GLMT.

Research Topic / Interest

Contact me to know my current interests.

Publications

These include only those published in our lab.

1. Comparative Study of the Real-Time Optical Trapping in the Rayleigh Regime for Continuous and Pulsed Lasers. S. N. Bandyopadhyay, T. Gaur, and D. Goswami, (2020) [Abstract] [PDF] [BibTeX]

   Abstract: Simulating real-time scenarios to predict optical trapping behavior for continuous wave (CW) as well as femtosecond pulsed lasers is a challenging problem. This is especially so, because, for a tightly focused laser, one must also include optical Kerr effect as well as thermal nonlinearity. We show here the distinct differences between CW and femtosecond pulsed laser mediated optical trapping via their effect in scattering and gradient forces in the Rayleigh regime. In our newly developed model, it will also be easier to predict the stability of the trap in real optical trapping scenario as well as provide information regarding choice of solvents, probes, and optical parameters like laser type, power range, wavelength, etc. as may the cases be.

    BibTeX: @unpublished{bandyopadhyayComparativeStudyRealtime2020,
     title = {Comparative Study of the Real-Time Optical Trapping in the {{Rayleigh}} Regime for Continuous and Pulsed Lasers},
     author = {Bandyopadhyay, Soumendra Nath and Gaur, Tushar and Goswami, Debabrata},
     date = {2020-02-01},
     eprint = {2002.00227},
     eprinttype = {arxiv},
     eprintclass = {physics},
     url = {http://arxiv.org/abs/2002.00227},
     urldate = {2020-02-06}
   }
   

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

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

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

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

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

    BibTeX: @inproceedings{gaurManifestingEffectsThermal2020,
     langid = {english},
     location = {{New Delhi, India}},
     title = {Manifesting the {{Effects}} of {{Thermal Nonlinearity}} in {{Optical Trapping}} for {{Rayleigh Regime}}},
     isbn = {978-90-825987-5-9},
     url = {https://my.pcloud.com/publink/show?code=XZqaxr7ZmnVNxAn4Y4mRbGS3d4A7FjmCWEv7},
     doi = {10/gf5mqf},
     eventtitle = {2019 {{URSI Asia}}-{{Pacific Radio Science Conference}} ({{AP}}-{{RASC}})},
     booktitle = {2019 {{URSI Asia}}-{{Pacific Radio Science Conference}} ({{AP}}-{{RASC}})},
     publisher = {{IEEE}},
     urldate = {2019-08-01},
     date = {2019-03},
     pages = {1-5},
     author = {Gaur, Tushar and Bandyopadhyay, Soumendra Nath and Goswami, Debabrata}
   }