Stimulated Brillouin and Raman scattering from a randomized laser beam in large inhomogeneous collisional plasmas. I. Experiment

Experiments have been conducted at the LULI (Laboratoire pour l'Utilisation des Lasers Intenses) multibeam laser facility to study in detail stimulate d Brillouin (SBS) and Raman (SRS) scattering from an intense (mean average intensity up to 10(14) W/cm(2)) long (600 ps full width at half-maximum) la ser beam interacting with thin exploded plastic foils. The plasmas are well characterized and the vacuum laser intensity distribution is well known du e to using either random phase plates or polarization smoothing. Direct and simultaneous Thomson scattering measurements of the associated plasma wave s allow us to obtain detailed information about the SBS and SRS temporal ev olution and spatial localization. These data are being used to benchmark a statistical model of SBS and SRS from self-focused speckles. The results of this comparison will be presented in a companion paper. The analysis shows that both SBS and SRS are originated from self-focused speckles and reveal s that plasma heating has an important effect on speckle self-focusing. (C) 2000 American Institute of Physics. [S1070- 664X(00)02011-5].