Enhanced forward scattering in the case of two crossed laser beams interacting with a plasma

The nonlinear enhancement of large-angle forward scattering of two identica l laser beams propagating in a preformed plasma has been observed experimen tally. The spectral analysis of the forward-scattered light shows two compo nents, one which is unshifted with respect to the initial laser light frequ ency, and the other which is redshifted by a few angstroms. The redshifted component is found to be strongly enhanced in the case of crossed beam inte raction in comparison with that of one beam illumination. Two-dimensional n umerical simulations show that this enhancement is due to large-angle forwa rd stimulated Brillouin scattering in which each beam serves as seed for th e forward scattering of the other.