Stochastic acceleration of electrons in fluctuating fields induced by stimulated Raman scattering in subrelativistic laser-plasma interactions

Stimulated Raman scattering (SRS) plays a crucial role in the energy conversion process from lasers to plasmas in the subrelativistic regime, where laser intensities range around 10 15 – 16 W/cm 2 . SRS induces excitations of Langmuir waves (LWs) and density fluctuations, such as plasma density cavities. These excitations modify laser absorption in underdense plasma regions and subsequently generate suprathermal hot electrons (HEs) that transport laser energy into overdense plasma regions, changing plasma dynamics, including shock wave formation and propagation. In this paper, we report saturations of SRS-induced HE generation within tens of picoseconds under continuous laser irradiation and a mechanism for HE generation driven by a stochastic process. One-dimensional particle-in-cell simulations with a large density-scale plasma ( ∼ 10 2 µ m ) over durations of up to 100 ps reveal the clear transition of the electron acceleration mechanism from previously reported electron trapping by SRS-excited LWs to a stochastic acceleration that produces fast electrons with mean energies greater than 100 keV as a result of random walks in fluctuating electric fields generated by SRS-induced density perturbations.