Saturation of backward stimulated Raman scattering and enhancement of laser light scattering in plasmas

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Abstract
Theoretical and numerical calculations are performed using the system of Zakharov and electromagnetic wave equations, to describe the nonlinear behavior of stimulated Raman scattering (SRS) in a finite homogeneous plasma slab. The enhancement of secondary scattering processes due to the nonlinear SRS saturation is investigated. The parametric decay of the resonantly driven Langmuir wave provides a mechanism which saturates SRS and greatly broadens the Langmuir and ion acoustic wave spectra. These enhanced electrostatic fluctuations scatter the incident electromagnetic radiation. Scaling laws for enhanced Brillouin, forward Raman, and anti-Stokes forward and backward Raman scattering as well as criteria for their strong enhancement are given. The frequency spectra of enhanced Brillouin scattering shows red- and blue-shifted components, with different amplitudes depending on the plasma density and laser intensity. The numerical results have been compared with experimental data providing new or alternative explanations for the observations.