Stimulated Raman and Brillouin scattering of polarization-smoothed and temporally smoothed laser beams

Abstract

Control of filamentation and stimulated Raman and Brillouin scattering is shown to be possible by use of both spatial and temporal smoothing schemes. The spatial smoothing is accomplished by the use of phase plates [Y. Kato and K. Mima, Appl. Phys. 329, 186 (1982)] and polarization smoothing [Lefebvre et al., Phys. Plasmas 5, 2701 (1998)] in which the plasma is irradiated with two orthogonally polarized, uncorrelated speckle patterns. The temporal smoothing considered here is smoothing by spectral dispersion [Skupsky et al., J. Appl. Phys. 66, 3456 (1989)] in which the speckle pattern changes on the laser coherence time scale. At the high instability gains relevant to laser fusion experiments, the effect of smoothing must include the competition among all three instabilities.