Low-level saturation of Brillouin backscattering due to cavity formation in high-intensity laser-plasma interaction.

Full particle-in-cell simulations of Brillouin backscattering in the high-intensity regime are presented. The final state of the strongly nonlinear evolution of the ion-acoustic wave packet consists of its collapse and the formation of a density cavity which is supported by large-amplitude localized electromagnetic fields. The cavitation manifests itself in large oscillations of the reflectivity which is terminated by a low-level saturation with strong kinetic effects. This newly discovered scenario demonstrates the importance of fully kinetic descriptions of Brillouin backscattering for high intensities.