Advanced model for SBS of a randomized laser beam and application to polarization smoothing experiments with preformed underdense plasmas

摘要

A model is presented, which describes the stimulated Brillouin scattering (SBS) of a randomized laser beam interacting with an underdense, expanding plasma. The model accounts for the self-focusing of speckles in the regime where plasma heating has an important effect on speckle self-focusing and on SBS threshold and reflectivity. The model exhibits a good agreement with SBS levels measured at the LULI multi-beam facility for a broad range of the laser and plasma parameters and both types of beam smoothing - RPP and polarization smoothing (PS). The model and experiments confirm that the PS technique allows to control the SBS level more efficiently than RPP.