Relativistic mirrors in plasmas. Novel results and perspectives

Relativistic flying mirrors in plasmas are thin, dense electron or electron-ion layers accelerated by high-intensity electromagnetic waves to velocities close to the speed of light in the vacuum; in nonlinear media, refractive index modulations are induced by a strong electromagnetic wave. The reflection of the electromagnetic wave from the relativistic mirror results in its energy and frequency changing. In the counter-propagation configuration, the frequency of the reflected wave is multiplied by the factor proportional to the gamma-factor squared. This scientific area promises the development of sources of ultrashort X-ray pulses in the at to second range. The expected intensity will reach the level at which the effects predicted by nonlinear quantum electrodynamics start to play a key role. In the copropagating configuration, the energy of the electromagnetic wave is transferred to the ion energy, providing a highly efficient acceleration mechanism.