Studies of stimulated Raman scattering in a plasma filament

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Abstract
The effect of a plasma filament on the characteristics of stimulated Raman scattering is examined. The model representation of the filament allows an assessment of the way in which Raman growth rates are influenced not only by the density inhomogeneity transverse to the beam direction, but by the nonuniform intensities of the incident laser and scattered light, as well as by Landau damping in the plasma. The model determines global eigenvalues without recourse to local (WKB) approximations, or to phenomenological damping factors. In shallow filaments the concentration of the light gives rise to modest gains in growth, while for deeper filaments the effects of the inhomogeneity and of Landau damping are dominant and suppress the instability. In both cases the strongest growth occurs at the bottom of the filament. Waveguide effects in deep filaments can result in emission being constrained to wavelengths significantly shorter than twice that of the incident laser light.