Stimulated Raman scattering in large plasmas

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Abstract
In long pulse, high‐energy experiments (4000 J, 2 nsec, 5×1014 W/cm2, 1.064 μm) at the Shiva laser facility, several percent of the laser light has been observed to be Raman scattered. The spectrum of the Raman‐scattered light was measured from 1.48 to 2.17 μm. The Raman scattering occurred principally at electron densities much lower than the quarter‐critical electron density. The high‐energy electrons expected in Raman scattering were observed indirectly in these experiments via their bremsstrahlung radiation. Additional experiments show that the Raman instability has a much lower intensity threshold for longer laser pusle length and larger laser spot size. Raman light measurements for 5320 Å irradiated disk target experiments are also reported. The light near 2λ0 or 1.064 μm had both a red‐ and blue‐shifted component. At high intensities, Raman scattering also occurred in the very underdense plasma.