Modulational and Raman instabilities in the relativistic regime

Abstract

A large amplitude electromagnetic wave propagating in a plasma is known to be subject to severe modulational and Raman instabilities. Previous works were devoted to the weakly relativistic limit and applied mainly to a cold underdense plasma. One extends these works to include the fully relativistic limit for a circularly polarized light for which one derives the dispersion relation in a one-dimensional plasma. The characteristics of the instabilities are also calculated in the case where the plasma is classically overdense, with 1<(ωp/ω0)2<γ, where ωp is the plasma frequency, ω0 is the laser frequency, and γ is the relativistic factor of an electron in the laser field. Particle-in-cell simulations confirm the results of the numerical solutions of the dispersion relation. For (ωp/ω0)2/γ=0.57 the growth rate can be as large as 0.52ω0. The nonlinear stage of the instability results in a strong heating of the electron distribution function. The theory is further extended to the case of an initially hot plasma, for which the dispersion relation of the instabilities is established. Its analytical solution is given in the case of a low density plasma. Particle-in-cell simulations are used to treat the general case. One observes a strong reduction of the growth rate of the instability, which tends to restore the possibility to propagate relativistic waves in plasmas.

Identifying the source of super-high energetic electrons in the presence of pre-plasma in laser–matter interaction at relativistic intensities

“…It was shown that [39][40][41], for a relativistic laser with laser amplitude a > 1 and homogeneous density close to relativistic critical, the nonlinear stage of the instabilities will result in a strong heating of the electron distribution function. The existing analyses are restricted to homogeneous plasmas.…”

Effects of relativistic electron temperature on parametric instabilities for intense laser propagation in underdense plasma

“…Figures 1(b) and 1(c) show the dispersion curves for the relativistic laser amplitudes. At low temperatures, the instability region becomes wider and growth rates become larger at higher laser amplitude and plasma density, in the meanwhile, the instability can develop even when the plasma density is higher than the quarter critical density as clarified before 16,21 . At a 0 = 3 and n e0 = 0.3n c , where…”

The sources of super-high energetic electron at relativistic circularly-polarized laser-solid interactions in the presence of large scale pre-plasmas

“…It was shown that [7][8][9], for the relativistic CP laser radiation with a 0 ≫ 1 and homogeneous density close to relativistic critical, one cannot distinguish these (M and RS) different modes, and the wave numbers of unstable modes have a broad range. While in our case, plasma is inhomogeneous rather strongly, so that if the existing conclusions match our cases need another further study.…”