Effect of the speckle self-focusing on the stationary SBS 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 the SBS reflectivity from an individual speckle, while above the critical power the pump power depletion due to SBS prevents strong SF and limits the maximum laser intensity in a speckle. The parameters that control 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 averaged SBS reflectivity of the randomized laser beam are revealed and their manifestations in recent SBS experiments with preformed plasmas are discussed. Physics of Plasmas 4(12) (1997) PACS numbers: 52.40.Nk, 52.35.Mw, 52.35.Nx, 42.65.Jx Typeset using REVT E X I. INTRODUCTION A lot of experimental and theoretical work has been devoted to the study of parametric..