STIMULATED BRILLOUIN-SCATTERING REFLECTIVITY IN THE CASE OF A SPATIALLY SMOOTHED LASER-BEAM INTERACTING WITH AN INHOMOGENEOUS-PLASMA

The stimulated Brillouin scattering (SBS) instability is investigated theoretically in the case of a spatially smoothed laser beam interacti ng with an inhomogeneous plasma in the regime of strong ion acoustic d amping. The domain of parameters being considered corresponds to most of the present day experiments carried out with nanosecond laser pulse s interacting with preformed plasmas: the characteristic length for co nvective amplification is assumed to be much shorter than the longitud inal correlation length of the laser field. The SBS reflectivity of on e individual hot spot is analytically computed taking into account the rmal noise emission and pump depletion within the hot spot. The SBS re flectivity of the whole beam is then obtained by summing up the indivi dual hot spot reflectivities in accordance with their statistical dist ribution. (C) 1997 American Institute of Physics.