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X and gamma rays --Even more powerful

June 13, 2019

International group of researchers including scientists from Skoltech have invented a new method for the generation of intense X and gamma-ray radiation based on Nonlinear Compton Scattering. Their results were published in the prestigious Physical Review Letters journal and the invention is about to get an international patent.

The Compton Effect is similar to playing tennis but in an unusual way. An electron plays the role of the racket and a photon plays the role of the ball. A photon being reflected from the fast electron racket acquires additional energy. It cannot fly even faster - the speed limit forbids that, but it can easily change its color, i.e. wavelength. Using this simple game, one can transform the wavelength of the incoming photon from the visible range to X and gamma-rays. Hard photon sources based on Inverse (linear) Compton Scattering are widely used throughout the world and typically consist of the electron accelerator and the laser system. The main advantage of such sources is the possibility to generate a narrow bandwidth radiation with the wavelength easily tunable by changing the energy of the electrons.

The most straightforward way to increase the number of generated X and gamma-ray photons is to increase the intensity of the laser system. In other words, the more compactly packed is the laser radiation in space (considering that the diffraction is small), the more scattering events between laser photons and electrons there will be.

This is well known together with the fact that increasing the power of the laser radiation in Compton Scattering leads to considerable spectral broadening. This is due to the light pressure, which slows the electrons down. In other words, our tennis racket while reflecting myriads of small tennis balls at once is slowed down; hence, the reflected balls will receive less energy. The problem here is that powerful laser radiation is not continuous, but rather comes as pulses in time. The intensity of powerful laser pulses first slowly grows and then slowly dies out. Consequently, the light pressure is non-uniform and the slow-down of the electrons is different at different moments of time leading to different energy of reflected photons.

The scientific team including Skoltech Professor Sergey Rykovanov invented a new method for generation of intense monoenergetic X and gamma-ray radiation based on Nonlinear Compton Scattering.

Sergey Rykovanov, a Professor from Skoltech's Center for Computational and Data-Intensive Science and Engineering:

"Such spectral line broadening is parasitic since we want to obtain a narrow bandwidth photon source with a well defined wavelength. Together with Vasily Kharin from Research Institute in Moscow and Daniel Seipt from University of Michigan in USA we invented a very simple method to remove the parasitic Compton line broadening for intense laser pulses and significantly increase the number of generated X and gamma-ray photons. To do this one has to carefully tune the frequency of the laser pulse (in other words to chirp it) so that it corresponds to the laser pulse intensity at each moment of time. For optimal effect, we proposed to use two linearly and oppositely chirped laser pulses propagating with a certain delay to each other. In my opinion, the beauty of our work is in its simplicity. To be entirely honest, we were very surprised how simply and smoothly everything worked out."

The new invention can significantly increase the brightness of modern and future synchrotron sources for research in medicine, nuclear physics and material science.

The scientists note that part of the simulations was performed on Skoltech's flagship supercomputer, "Zhores", named after the Nobel laureate Zhores Alferov.

Skolkovo Institute of Science and Technology (Skoltech)

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