Stimulated Brillouin scattering with a 1 ps laser pulse in a preformed underdense plasma

An experimental study of stimulated Brillouin scattering (SBS) with a 1 ps laser pulse in a large underdense preformed plasma is presented. It is shown that the SBS reflectivity increases from 10-4 to 10-1 as the intensity of the interaction beam rises from 5×1014 to 1016 W/cm2; for intensities between 1016 and 1017 W/cm2, a saturation level at 10% is experimentally established. This experimental result is compared with theoretical estimates of time-integrated SBS reflectivity in the transient phase of the so-called modified decay regime. The latter results are seen to be consistent with the experimental data provided that there exists a nonthermal noise in the plasma depending on the laser intensity.