Modification of spatial and temporal gains of stimulated Brillouin and Raman scattering by polarization smoothing

Significant reductions of stimulated Brillouin (SBS) and Raman (SRS) scatte ring are measured by adding polarization smoothing (PS) to a random phase p late smoothed beam. The associated plasma waves, as measured by Thomson sca ttering, are spatially and temporally modified and reveal that the interpla y between SBS and SRS has to be taken into account to understand the effect of the smoothing. The results also support the numerical simulations [S. H uller et al., Phys, Plasmas 5, 2706 (1998); R. Berger et al., Phys. Plasmas 6, 1043 (1999)] predicting a reduction of self-focusing with PS, resulting in a decrease of the maximum laser intensity and consequently of SBS and S RS gains.