Influence of Spatial and Temporal Laser Beam Smoothing on Stimulated Brillouin Scattering in Filamentary Laser Light

Three-dimensional simulations are presented which calculate the time-dependent, self-consistent evolution of filamentation and stimulated Brillouin backscatter (SBBS) in nonuniform laser beams with intense hot spots. The simulations show significant reflectivity ( $>$1%) for modest average-intensity gain exponents (5–10). Many hot spots cooperate to produce a total SBBS amplification that increases with the plasma length as well as hot-spot length. Temporal beam smoothing with bandwidth comparable to the SBBS growth rate substantially reduces the nonuniform-laser-beam reflectivity.