In July 2016, an article “Inverse Faraday Effect Driven by Radiation Friction” coauthored by MEPhI researchers, the University of Rostock (Germany) and the University of Pisa (Italy) was published in New Journal of Physics. The article has been included into the digest of an international web magazine physicsworld.com. During the first three weeks after the publication, it was downloaded from the journal webpage for more than 1000 times. One of the coauthors, Prof. Sergey Popruzhenko from the Department of Theoretical Nuclear Physics has explained to us the scientific community’s high interest provoked by this purely theoretical work.
Sergey Popruzhenko is a Dr. of Science and Professor at MEPhI Department of Theoretical Nuclear Physics. He is an expert in the field of interaction of intense laser radiation with matter, who is the coauthor of over 60 scientific publications. S. Popruzhenko graduated from MEPhI in 1997. During his scientific career he worked as a researcher and visiting scientist at several European research centers and universities including the Max Planck Institute for Nuclear Physics (Heidelberg, Germany), the Nuclear Research Center Saclay (France), the Max Born Institute for Nonlinear Optics and Fast Spectroscopy (Berlin, Germany) and the University of Rostock.
Question: What is the novelty of your work? In your opinion, why was it noticed by physicsworld.com?
S.P.: In our paper, we present calculations, which suggest a new method for the generation of extremely strong magnetic fields in the lab. Under “extremely strong” I mean magnetic fields with strength of several giga-Gauss (109 Gauss). Currently available values are at least one order less in magnitude. In nature such superstrong fields exist perhaps only in the space. Therefore, generation of such field in laboratory conditions provide new opportunities for modeling of astrophysical processes. A new research field – laboratory astrophysics – has emerged relatively recently, and now it is very fast-developing. Our work is of particular interest because it suggests new opportunities in this field.
The Faraday effect itself has been known for a long time (as its name suggests). It means that the polarization plane of an electromagnetic wave, propagating through a non-magnetic medium, is rotating in the presence of a constant magnetic field. An inverse process means the generation of a magnetic field during the propagation of a circularly polarized wave through a crystal or plasmas. It was considered theoretically in the 60-es by a soviet and Russian theorist Lew Pitaevsky, a famous representative of Landau’s school. The stronger the wave, the higher magnetic field it can generate propagating through a medium. However, the peculiarity of the effect is that it requires absorption for its very existence, i.e. it does not take place in entirely transparent media. In highly intense electromagnetic fields electrons become ultrarelativistic, which considerably reduces their collisions, making conventional absorption suppressed. In our work we show, that at very high laser wave intensities the absorption can be effectively provided by radiation friction, instead of binary collisions. This specific friction finally leads to the generation of superstrong magnetic field. I think that our work has raised interest, which is proved by a high number of downloads and mentioning in the news of physicsworld.com, is connected mostly with magnetic fields of a very high magnitude. Large numbers always attract attention. It is funny enough, that we sent the paper to New Journal of Physics after it had been rejected by Physical Review Letters with an explanation, that the obtained results are barely interesting for a broad physicists’ community.
Question: Who took part in the work?
S.P.: This work was done in a small international group. Andrea Macchi from the University of Pisa is well known for his contribution into the theory of laser plasma. Tatyana Liseykina from the University of Rostock and the Institute for Computational Technologies RAS is a leading world expert in numerical modeling of plasma. The combination of theoretical methods and numerical experiment has allowed not only estimate the value of the effect but also develop a physically transparent explanation in terms of radiation friction. This makes the result clearer and more appealing.
Question: Is that possible to check your calculations experimentally? If yes, what is required to conduct an experiment?
S.P.: It would be possible in the nearest future, but not immediately. Actually our work was essentially stimulated by the fact that several new laser facilities of record power will be completed in the next 3-5-10 years. Three of such lasers are now under construction within the European project Extreme Light Infrastructure (ELI) in the Czech Republic, Romania and Hungary. The fourth pillar of even higher power called Exawatt Center for Extreme Light Studies – XCELS is under the development at the Applied Physics Institute RAS at Nizhny Novgorod. By the way, MEPhI is included into the road map of this project. These laser facilities will allow reach intensities required for the generation of superstrong magnetic fields due to the radiation friction and also for the observation of many other fundamental strong-field effects.
I have to admit that in the past years there is a boom in the area of superstrong laser fields – because technical capabilities of the currently constructed laser sources will allow approach very closely the new physics – nonlinear quantum electrodynamics of vacuum. MEPhI is considered to be one of the international leading centers for the theory of interaction of superintense laser fields with matter and with vacuum. A great contribution into the leadership of our University was made by Nikolay Borisovich Narozhny, who was one of the founders of this research field and did a lot for its development at MEPhI. At the present time, there are serious plans to establish a modern experimental laboratory in high-power laser physics in our University. Next year, the construction of a kilo-Joule laser facility will begin in the new laboratory building. In its main parameters, this Experimental Laser Facility (ELF) will overtake several similar laser pillars operating in leading foreign universities. Based on the ELF, an international user center, open for experimental groups from different countries, will be founded. The realization of this project could help our University to achieve international leadership in experimental laser physics in addition to our success in the theory.
