A Local-Field Approach to Understanding Multibeam Laser–Plasma Instabilities*

Laser–plasma instabilities such as stimulated Raman scattering and two-plasmon decay present a major challenge for laser-driven inertial confinement fusion. Predicting the severity of these instabilities requires a model that captures the complex, 3-D interaction of multiple laser beams, including effects such as speckle, polarization, and bandwidth. Analytic approaches typically employ the frequency and wave-vector matching condition for multiple laser beams to drive a shared daughter wave while neglecting the local field structure that results from the interference between many overlapping beams. Three-dimensional simulations, on the other hand, capture the full interaction dynamics and field structure but can obscure the underlying physical processes. Here we introduce an intermediate approach that uses a simplified model of the local field structure to study the impact of multibeam interactions on absolute instabilities.