Saturation of stimulated Raman scattering by Langmuir and ion-acoustic wave coupling

Studies of stimulated Raman scattering (SRS) based on the one-dimensional Zakharov–Maxwell equations for homogeneous, finite plasmas are presented for a wide range of parameters relevant to current laser–plasma interaction experiments. It was found that the primary mechanism responsible for saturation of SRS is the parametric decay instability (PDI) of the resonantly driven Langmuir wave. The different spatiotemporal evolution of SRS (convective) and PDI (absolute) leads to new physics in SRS nonlinear evolution, including disruption of PDI cascade, localization of Langmuir fields, and burstlike behavior of SRS reflectivity. The asymptotic saturation levels are well approximated by a simple scaling law, which is proportional to the PDI threshold and depends on the SRS convective gain factor.