Experimental demonstration of optical mitigation techniques for stimulated Brillouin Scattering in ignition relevant plasmas*

Inertial confinement fusion (ICF) and high energy density physics experiments require intense and energetic laser beams to propagate efficiently through long plasmas. A series of experiments performed at Omega will be presented that study the effects of SSD, polarization smoothing, and laser beam defocusing on mitigating stimulated backscatter, filamentation, and beam spray. We measure a factor of 1.8 reduction in the stimulated Brillouin scattering (SBS) when polarization smoothing is applied; no effect on the SBS is observed when up to 3 angstroms of smoothing by spectral dispersion (SSD) is applied. Furthermore, we show that the SBS reflectivity is controlled by either reducing the laser beam intensity or defocusing. The results from these experiments compare well to linear theory as modeled in 3 dimensions by pf3D.