# Relativistic flying forcibly oscillating mirror

Note: This is a copy of press-release of the paper by J. Mu et al., Phys. Rev. E 102, 053202 (2020) which I co-authored. You can find the original article here.

With the help of analytical modeling and large-scale computer simulations, a team of authors from Kansai Photon Science Institute (Japan) and ELI Beamlines (Czech Rep.) found novel physical realization of the relativistic mirror, the relativistic flying forcibly oscillating mirror (RFFOM). It combines the properties of the relativistic flying mirror and relativistic oscillating mirror. In addition, due to strong periodic modulations of the mirror surface, it acts as a reflective diffraction grating, according to a paper recently published in Physical Review E.

### Relativistic mirrors

A relativistic mirror may be defined as an object that reflects incoming radiation while moving at relativistic velocity. The electromagnetic wave reflected from a relativistic mirror in a counter-propagating configuration is compressed, amplified and its frequency is upshifted due to the double Doppler effect. Albert Einstein used the concept of relativistic mirrors to illustrate the theory of special relativity in his seminal paper in 1905. Later, it turned out that relativistic mirrors can be realized by irradiating plasma targets by intense laser pulses. Relativistic mirrors are currently studied in many different contexts because of their great potential for both fundamental science (e.g. light intensification towards the Schwinger limit, investigation of photon-photon and Delbruck scattering, detection of Hawking radiation and the information loss paradox) and practical applications (e.g. attosecond spectroscopy, molecular imaging, plasma diagnostics).

### Novel physical realization

The RFFOM appears as a cusped mirror, the low-dimensional region of highest electron density at the joining of the electron cavity wall and the bow wave excited by the intense laser pulse (driver) propagating in plasma (see Figure 1 and Figure 2). The RFFOM undergoes forced oscillations imposed by the driver pulse and moves with the group velocity of the driver. It efficiently reflects a counter-propagating laser pulse (source). The reflected radiation spectrum exhibits well-pronounced diffractive orders and harmonic orders. The base frequency of the reflected radiation and correspondingly all harmonic orders are strongly upshifted with respect to the base frequency of the incident source pulse, due to the double Doppler effect. The described scheme can be used for the generation of bright sources of high-frequency radiation. Its realization is easier than the relativistic flying mirror, where one should maintain a sufficiently slow approach to longitudinal wave breaking.

### How to cite

J. Mu, T. Zh. Esirkepov, P. Valenta, Y. Gu, T. M. Jeong, A. S. Pirozhkov, J. K. Koga, M. Kando, G. Korn, and S. V. Bulanov, “Relativistic flying forcibly oscillating reflective diffraction grating”, Physical Review E 102, 053202 (2020).

@article{PhysRevE.102.053202,
title = {Relativistic flying forcibly oscillating reflective diffraction grating},
author = {Mu, Jie and Esirkepov, Timur Zh. and Valenta, Petr and Gu, Yanjun and Jeong, Tae Moon and Pirozhkov, Alexander S. and Koga, James K. and Kando, Masaki and Korn, Georg and Bulanov, Sergei V.},
journal = {Phys. Rev. E},
volume = {102},
issue = {5},
pages = {053202},
numpages = {9},
year = {2020},
month = {Nov},
publisher = {American Physical Society},
doi = {10.1103/PhysRevE.102.053202},