EFFECT OF THE SPECKLE SELF-FOCUSING ON THE STATIONARY STIMULATED BRILLOUIN-SCATTERING REFLECTIVITY FROM A RANDOMIZED LASER-BEAM IN AN INHOMOGENEOUS-PLASMA

The effect of laser light self-focusing (SF) in speckles on stimulated Brillouin scattering (SBS) in an inhomogeneous plasma is studied. It is found that below but near critical power SF dramatically enhances t he SBS reflectivity from an individual speckle, while above the critic al power the pump power depletion due to SBS prevents strong SF and li mits the maximum laser intensity in a speckle: The parameters that con trol the SBS/SF interplay are the ratio of plasma inhomogeneity scale length to the speckle length and the product of the plasma density and the speckle cross section. The consequences of the SF effect on the a veraged SBS reflectivity of the randomized laser beam are revealed and their manifestations in recent SBS experiments with preformed plasmas are discussed. (C) 1997 American Institute of Physics.