Measurements of Green Laser-Beam Propagation and Backscatter in Long-Scale Length Plasmas

Summary form only given. We have implemented a complete set of optical diagnostics at the Omega laser to measure propagation and backscatter of a green (527 nm) high intensity laser beam (10¹⁵ W/cm²) in large-scale length, laser produced plasmas. The diagnostics include a transmitted beam diagnostic (TBD), a full aperture backscatter station (FABS) as well as a near backscatter imager (NBI) to simultaneously measure forward and backward scattered light with temporal, spectral and spatial resolution. Heating a mm-size gasbag or hohlraum target with up to 36 defocused heater beams, delivering a total energy of up to 16 kJ in a 1 ns pulse, creates a plasma at a density around 6times10²⁰ cm^-3 and temperatures of several keV. We observe a reduction of the beam transmission with increasing probe beam intensity, consistent with the onset of parametric scattering instabilities. Beam propagation can be significantly improved, by applying temporal- or polarization-beam smoothing. Our results indicate good beam propagation in ignition scale plasmas for inertial confinement fusion