Stimulated forward Raman scattering in large scale-length laser-produced plasmas

A forward stimulated Raman scattering (FSRS) diagnostic was developed for the 60 beam Omega laser facility to investigate the propagation of an intense ( ~ 8 × 1014 W/cm2), frequency doubled Nd:glass laser beam ( ≤ 360 J, 527 nm, 1 ns) through a mm-scale laser-produced plasma. Forward scattered light was measured with spectral, and temporal resolution using a streaked spectrometer and an absolutely calibrated photo-multiplier. We present a detailed description of the instrument, the calibration methods, as well as the first forward Raman scattering measurements from hot ( ~ 2 keV), dense (5.5 × 1020 cm−3) laser-produced plasmas. These results are of interest to laser-driven inertial fusion at the National Ignition Facility where larger plasma scales could potentially lead to higher FSRS gains. In addition, simultaneous measurements of stimulated forward and backward scattered light present an unambiguous method for determining plasma density and temperature.