At the forefront of science: how can we visualize a vacuum? An interview with Academician Khazanov.

— How long have you been involved in science?

— I would say since university. At that time, it was still the Gorky Polytechnic Institute. In 1982, I enrolled in the Faculty of Radioelectronics and Technical Cybernetics.

— What does “engaging in science” mean to you?

— It means establishing truths that have not yet been discovered. Through various means. Through contemplation, calculations on paper, and of course, through experimentation. Physics is primarily an experimental science, and I mainly conduct experiments in my research. Naturally, nowadays a very useful tool for physicists is the computer. It significantly expands the capabilities of any scientist, not just physicists.

— Did you have any interest in exploring the world as a child? Was there anyone in your family who was involved in science or worked in this field?

— No, no one in my family was connected to science. My mother is a surgeon, and my father was a journalist and playwright, working as an editor at Gorky Television from its inception. I wouldn’t say that I had a particularly strong interest in scientific activities as a child, but I was very passionate about physics and mathematics since school. These were my favorite subjects. Apparently, this is how I ended up choosing my profession.

— Where did you study, and what was your attitude toward education?

— I attended an ordinary school that was simply close to my home, School No. 11 in Nizhny Novgorod. I can't say that my school years were particularly special or memorable. I didn't enjoy studying much, but I found the material in mathematics and physics interesting. I studied many things on my own. I read popular science books. I can't remember specific titles now, but something like “Entertaining Physics” and “Entertaining Mathematics.” I also participated in Olympiads.

— So you had already decided on your specialty back in school?

— Well, generally speaking, yes, although I played chess at almost a professional level, and there was a possibility to turn that hobby into a profession. But I chose science.

— In what area of physics did you work during your student years?

— I got involved with lasers right from the start and, in a broad sense, I haven’t changed that theme much since. However, within that theme, I have engaged in very different activities and research. In other words, the focus of my research has changed several times throughout my life, but it has always remained within the realm of optics.

— But choosing a direction and actively working in it is only part of the success. I think it's very important for a student to have a good and interested mentor. Do you agree with this statement, and who do you consider your mentor?

— Yes, absolutely. I actually had two scientific supervisors. One was Herman Aronovich Pasmannik, who is now in America. He prepared me more in the theoretical part. The second was Nikolai Fyodorovich Andreev, head of the laboratory of pulsed solid-state lasers at IPF RAS. He taught me experimental research. I worked side by side with him in the same room, sitting at adjacent desks for many years. This was very important and had a significant impact on all my subsequent activities. In this sense, I was certainly lucky.

I started working full-time in Nikolai Fyodorovich's laboratory right after graduation. Consequently, I had very little experience. But at that time, the laboratory was transitioning to a new type of laser. When I came to the laboratory during my internship, I participated in experiments on an old, well-studied setup. But then new pulsed lasers appeared, and Nikolai Fyodorovich and his laboratory took on the challenge of mastering them. In fact, I started all this with him, as they say, “from scratch.” Usually, this phrase refers to a writing desk, but in my case, it was an optical one. We began assembling mirror after mirror, element by element, until the entire setup was built. It was certainly challenging, but also interesting, and I learned a lot right away.

— What area are you currently working in? Why did you choose it, and how did you arrive at this point?

— I am working in the field of powerful pulsed lasers. My main task is to increase the efficiency of these lasers, not only in terms of power output but also in other aspects. Choosing this direction was, in part, a matter of circumstance. Initially, I studied powerful nanosecond lasers and the nonlinearity associated with the Mandelstam-Brillouin scattering. Later, I worked on thermal effects. This is also an area of powerful lasers, but here the average power is important rather than peak power, which inevitably generates a lot of heat. Consequently, all the problems and physics are related to this. These studies later allowed me to join the international project on gravitational wave detection, LIGO. I was introduced to this project by Alexander Mikhailovich Sergeyev (who later became the president of the Russian Academy of Sciences from 2017 to 2022. — ed.). It immediately became clear that one of the many (but nevertheless mandatory to eliminate) limitations on the detector's sensitivity required research in which I already had experience. As a result, I was able not only to understand the physics of the problem but also to devise a solution. A few years later, unique devices were created at IPF RAS that operated at high power—Faraday isolators, which fully met the needs of LIGO and continue to operate there around the clock to this day.

In the early 2000s, I began working with femtosecond lasers with high (again) peak power as part of a petawatt laser project in collaboration with RFNC-VNIIEF. In femtosecond lasers, the thermal component is not as critical. The main task in this field is to achieve high peak power for various fundamental experiments.

— As far as I know, scientists keep track of their field of research and related areas. What is the current situation in your field? What is the key task at the moment?

— Well, that depends on the horizon. One of the dreams on a distant horizon is to create a laser so powerful that its field is strong enough to explore the structure of the vacuum. The physical vacuum is not empty. It is a complex “device” with many hidden elements, and to reveal them, very strong fields are needed, which can only be achieved with a laser. This is a fundamental issue that has an accepted theoretical concept, but there has been essentially no experimental verification. This is perhaps the main task at present. Our laser is currently not powerful enough for such experiments, but there are many tasks that accompany this. Additionally, there is the physics of lasers itself, which aims to understand what currently limits parameters and how to improve them.

— Tell us about your latest research. What did you study, what methods did you use, and what results did you achieve? How do you plan to develop these results further?

— In the last year, I have been actively studying a device used in every powerful femtosecond laser—the optical compressor. It is used almost identically in every laser, but while developing the next generation of lasers, it became clear that the compressor limits the device's capabilities. We realized that among the fundamental questions, this one is key. And there are significant limitations that need to be figured out how to overcome. It turned out that we can move in this direction.

The problem is that the diffraction gratings used in the compressor are sensitive to powerful radiation. At today's technological level, the rest of the laser is ready for increased power, but they are not. Making them technologically less “finicky” and more stable is quite challenging. Despite researchers' efforts, progress in this area has been minimal. We began to investigate this issue and found several potential solutions. Firstly, we can modify the compressor's design to reduce the likelihood of optical breakdown and damage to the gratings. Secondly, we can optimize the compressor's parameters to increase the beam power without degrading its spatial characteristics. Thirdly, we can develop new methods for compensating for distortions caused by the compressor's operation.

The next problem is that the compressor must not only create a short pulse but also preserve its spatial properties. Strictly speaking, all optical elements are imperfect, but diffraction gratings degrade spatial properties in a specific way, and known methods for addressing this issue do not work here.

And, of course, once we understood this, it became clearer how to manufacture these gratings and how to use them correctly. Some things were obvious, while others were not. However, there are often various reasons, each leading to negative consequences. Typically, they act poorly individually, but together, the cumulative effect is even worse.