Gopal Dixit

Biography

Gopal Dixit Assistant Professor

Research Interest

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.