Measurement of the stimulated Brillouin scattering reflectivity from a spatially smoothed laser beam in a homogeneous large scale plasma

The dependence of the stimulated Brillouin scattering (SBS) reflectivity on both the focusing aperture and the incident laser intensity has been experimentally studied in the case of a spatially smoothed beam. The experiment was performed in millimeter size, homogeneous, stationary plasmas created by irradiating a helium gas jet. SBS was excited by a 1.053-mu m wavelength, 600-ps interaction beam at intensities up to 4 X 10(14) W/cm(2). The saturation level of SBS reflectivities was of the order of 10%. A good agreement between the experimental SBS thresholds and the theoretical ones obtained from the one-dimensional stochastic convective SBS model [Phys. Plasmas 2, 1804 (1995)] is observed.