4 WAVE SIDESCATTERING ABSOLUTE INSTABILITY OF STIMULATED BRILLOUIN BACKSCATTERING IN PLASMAS

A novel effect of sidescattering absolute instability due to stimulate d Brillouin backscattering (SBBS) has been theoretically predicted. Th e effect is based on four wave mixing of the driver pump, a backward p ropagating Stokes wave and two newly excited counterpropagating sidesc attered Stokes waves. It is shown that the instability of the sidescat tered Stokes components is absolute. The threshold value for this inst ability in the model of a homogeneous plasma slab is evaluated. The ef fect has ultimate importance for the explanation of the driver pump fi eld intensity dependence in SBBS encountered in laser-plasma interacti on experiments.