Coherent forward stimulated Brillouin scattering of a spatially   incoherent laser beam in a plasma and its effect on beam spray
  A statistical model for forward stimulated Brillouin scattering (FSBS) is developed for a spatially incoherent, monochromatic, laser beam propagating in a plasma. A threshold for the average power in a speckle is found, well below the self-focusing one, above which the laser beam spatial incoherence can not prevent the coherent growth of FSBS. Three-dimensional simulations confirm its existence and reveal the onset of beam spray above it. From these results, we propose a new figure of merit for the control of the propagation through a plasma of a spatially incoherent laser beam. 
M. Grech, G. Riazuelo, D. Pesme, S. Weber, V.T. Tikhonchuk