Gopal Dixit
Assistant Professor
Photograph: 
Phone: 
+91 22 25767558
Email: 
gdixit@phy.iitb.ac.in
Office: 

203

Research Interests: 
Currently I am looking  for motivated and brilliant Ph. D. and Postdoc co-workers, who could join my team to explore fascinating  aspects of studying microworld  in motion.  If you are interested to work on a thesis or a project with me, please visit my office or write me a mail.    

My research focuses on probing ultrafast processes in nature on attosecond and femtosecond timescales. My research interest include:

1. Four Dimensional Imaging of Electronic Motion: The motion of atoms within molecule and solid that is associated with physical and chemical transformations occurs on femtosecond (1 fs = 10-15 second) timescale, whereas the electronic motion can be even faster, on the order of attoseconds (1 as = 10-18 second) timescale. In order to understand the functionality and dynamic behavior of ultrafast physical, and chemical processes completely, it is essential to have a complete four-dimensional imaging (three spatial and one temporal) of electronic motion with sub-angstrom spatial and few-femtoseconds to several hundreds of attoseconds temporal resolutions, respectively, in real-space and in real-time. Moreover, imaging and manipulating the electronic motion on ultrafast timescale provide novel pathways towards controlling ultrafast processes. In this direction, we use time-resolved ultrafast x-ray scattering in pump-probe scenario where a pump laser pulse initiate the ultrafast process which is followed by the second probe pulse with duration shorter than the timescale of the ultrafast process. By varying the pump-probe delay time, we could record the current state of the process like a snapshot and obtain the individual images of a slow-motion electronic movie. Since electrons provide the glue that binds atoms together to form molecules, the ability to image and control electrons in matter could have revolutionary consequences for applications.

Apart from using time-resolved x-ray scattering and its different variants, we will also focus on the development of other time-resolved ultrafast x-ray spectroscopic methods such as time-resolved Raman scattering, time resolved x-ray absorption, time-, energy-, and angle-resolved photoelectron spectroscopic for probing ultrafast non-equilibrium electronic motion in matter.

2. TIME DELAY IN PHOTOEMISSION: 
When an ultrashort laser pulse with enough energy impinges on matter, laser pulse transfers the energy to the matter and subsequently electrons from various orbitals are kicked out from the matter. However, to know whether the response time to the absorption of light is finite leading to a time delay in photoemission or the ejection of the photoelectron occurs instantaneously was not possible until recently. A finite time delay between photoemission processes corresponding to different valence orbitals has been measured experimentally. A ubiquitous understanding in all these measurements is the dominant influence of electron correlations to determine the temporal behavior of ejected electrons. Understanding the response time of light to the matter has a very important role in pump- probe spectroscopy and can be used to calibrate time zero in pump-probe delay time with a precision of a few attoseconds. 


Selected Publications: 

1. Bredtmann T., Ivanov M. and Dixit G.: “X-ray imaging of chemically active valence electrons during a pericyclic reaction”  Nature Communication 5, 5589 (2014).

2. Santra R., Dixit G. and Slowik J. M.: “Comment on How to observe coherent electron dynamics directly” Phys. Rev. Lett. 113, 189301 (2014). 

3. Slowik J. M., Son S. –K., Dixit G., Zurek J. and Santra R.: “Incoherent x-ray scattering in single molecule imaging”  New. J. Phys. 16, 073042 (2014). 

4. Dixit G., Slowik J. M. and Santra R.:  “Theory of time-resolved non-resonant x-ray scattering for imaging ultrafast coherent electron motion” Phys. Rev. A 89, 043409 (2014).

5. Dixit G., Slowik J. M. and Santra R.:  “Proposed imaging of the ultrafast electronic motion in samples using x-ray phase-contrast” Phys. Rev. Lett. 110, 137403 (2013).

Appeared as a cover page in Phys. Rev. Letts.

(see also highlight in Nature Photonics 7, 423, 2013)

6. Dixit G., Chakraborty H. S. and Madjet M. E.: “Time delay in the recoiling valence-photoemission of Ar endohedrally confined in C60”  Phys. Rev. Lett. 111, 203003 (2013).

7. Dixit G. and Santra R.:  “Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets” J. Chem. Phys. 138, 134311 (2013).

8. Dixit G., Vendrell O. and Santra R.: “Imaging electronic quantum motion with light” Proc. Nat. Acad. Sci. U.S.A. 109, 11636 (2012).

(see also new and views in Nature Photonics 6, 645, 2012).

9. Magrakvelidze M., Madjet M. E., Dixit G., Ivanov M., and Chakraborty H. S.: Attosecond time delay in valence photoionization and photorecombination of argon: a TDLDA study Phys. Rev. A 91,  063415 (2015).

10. Magrakvelidze M., Anstine, D. M., Dixit G., Madjet M. E., and Chakraborty H. S.: “Attosecond structures from the molecular cavity in fullerene photoemission time delay” Phys. Rev. A 91, 053407 (2015).

11. Barillot T., Cauchy C., Hervieux P-A., Gisselbrecht M., Canton S. E., Johnsson P., Laksman J., Mansson E. P., Dahlstroem J. M., Magrakvelidze M., Dixit G.,  Madjet M. E., Chakraborty H. S. Suraud E., Dinh P. M.,  Wopperer P.,  Hansen K., Loriot V., Bordas C., Sorensen S., and Lepine F.: “Angular asymmetry and attosecond time delay from the giant plasmon resonance C60 photoionization”  Phys. Rev. A 91, 033413 (2015).

 

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