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.