AMA with Prof. Gopal Dixit

"Ask Me Anything!" with Prof. Gopal Dixit

Research Interests: 

Our research group focuses on probing ultrafast processes in nature on attosecond and femtosecond timescales. Our 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 timescale, whereas the electronic motion can be even faster, on the order of attoseconds 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.

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.

Ref : https://ultrafastlabiitb.wixsite.com

Questions and Answers:

What is your inspiration for poetry on facebook?

• Hmm!! I think you guys are talking about the poetries, which seem like intense and heart-broken. Unfortunately, I am sorry to disappoint you all. These poetries are the result of my attempt to keep in touch with my mother tongue: Hindi. As I spend almost a decade in Germany and I realized that I am losing my ability to write in Hindi. So I started writing. Now, I get motivation from different corners. I wish to write long poetry in the future.

Is there any scope for your Nature paper paving the way for some commercial technology? Will it affect our daily lives somehow?

• The main aim of our work, published in Nature Communications 2018, is to know the polarisation state of attosecond pulse, which has broad-energy bandwidth. The polarisation state of attosecond pulse changes shot to shot in time. So the polarisation state becomes time-dependent. In our work, we provided a method to know time-dependent polarisation and to distinguish the polarized, partially polarized and unpolarised pulse. Characterization of polarization of the pulse is essential to understand any chiral-sensitive light-matter interaction such as magnetization dynamics of spins, a distinction between left and right-handed chiral molecules. Chiral distinction is crucial in several research areas like drug-industry, biochemistry etc. The effect of the molecules depends on their handedness e.g. the same molecule but with different handedness is found in orange and lemon. Many biological molecules including DNA, proteins, lipids etc. have handedness. Therefore, understanding the chirality of molecules (handedness) is of utmost importance.

Why did you choose to get into academia instead of the industry?

• Creativity and freedom. More importantly, I have the freedom to switch from one research topic to other topics of my interest. I think such kind of freedom is not available in an industry generally. I would love to do some work in R&D sector, but not much work is going on in our country.

What captured your interest initially in the field of ultra-fast optics? Why did you get into it?

• After finishing my Ph. D. in atomic and molecular spectroscopy, I was exploring some exciting topics for my further research. This was the time when XFEL (x-ray free-electron laser) related research started and I got an opportunity to work on time-resolved x-ray scattering. Later, I explored other interesting topics such as Petahertz Electronics. Ultrafast optics or, I would say, ultrafast/attosecond science is the field where you could really explore several interesting questions and verify many fundamental aspects of quantum mechanics such as finding whether time is an operator or not, photoionization process is an instantaneous process or not, how to watch the bond-breaking or bond-making events during a chemical reaction, etc.

What are the main challenges that you face in your research?

• There are several challenges. The first and foremost is that few groups are working in attosecond science in our country. So, I am lacking an environment for scientific discussion and exchange of ideas. Both are the essential pillars for frontier research. Another aspect is not having enough awareness about attosecond science between academicians and researchers in our country.

Where do you get all your university t-shirts?

• I like having creative t-shirts. Whenever I see a uniquely designed t-shirt, I want to get a hold of it. But, sometimes my academic position and design of the t-shirt do not go hand-in-hand. Whenever I visit some university, I buy some souvenirs. T-shirts are one among many. Sometimes, I receive them as gifts from my colleagues around the globe.

What do you like to do in your free time? Any hobbies?

• Trying to understand the most complex thing in the World: have a guess... Other times, I like listening to songs and reading novels. I enjoy playing badminton too.

In what ways do you keep in touch with the advances in research in your field?

• My day starts with a cup of tea and arxiv and ends with leading journals like Phys. Rev. Letts., Nature, Science etc.

What advice do you have for UGs and PGs?

• If you like to excel in any given field or life in general, it is important to be fit mentally as well as physically. So, participate in different kinds of sports along with your academics. It is important to explore your hobbies too as IIT offers a plethora of activities. In short, I would say: Be the focus of the crowd not the part of it.

What do you think will be the next big thing in your field? How do you plan to be a part of

it?

• As you might be aware that the Nobel Prize in Physics for 2018 is awarded for ultrashort - intense laser pulse and its various applications. Now the scientific community is feeling that the next will be for attosecond science, sooner or later. Let me quote the lines from MIT technology review: “And hydrogen atoms will be just the start. It won’t be long before we have videos of the quantum motion of electrons in more complex molecules, perhaps even in biomolecules themselves. When that happens, we’ll be watching the quantum motion of life itself”. This is the big thing we all are waiting to happen and we all are contributing significantly in this direction. Here is the web-link of the full article: https://www.technologyreview.com/s/428614/imaging-the-quantum-motion-of-electrons-using-light/