Nonlinear plasma response to a slowly varying electrostatic wave, and application to stimulated Raman scattering

The nonlinear electronic susceptibility induced by an electrostatic wave slowly varying in space and time, which is the key parameter for the kinetic modeling of stimulated Raman scattering (SRS), is derived analytically. When calculating the real part of the susceptibility, by making the adiabatic approximation, account is taken of the amplitude dependence of the wave frequency. Then, the “loss of resonance” of a plasma wave is found to occur at much larger amplitudes than has been predicted by Rose and Russel [H. A. Rose and D. A. Russell, Phys. Plasmas 11, 4784 (2001)] using the constant-frequency approximation. The imaginary part of the susceptibility, from which is deduced the Landau damping rate of the plasma wave, is derived using two different approaches (perturbative or not) depending on the wave amplitude. It is shown to be a nonlocal function of the wave amplitude, which underlines the importance of interspeckle interactions in SRS.