Simulations Of Multi-beam Raman Amplification

Stimulated Raman scattering is an important topic in the study of laser and plasma interaction instability.It has attracted much attention in inertial confinement fusion re-search.When a laser beam is incident on a plasma,if the resonance condition is satisfied,an electron plasma wave is excited and a beam of scattered light is generated.This process is called Stimulated Raman scattering(SRS).Previous studies on SRS were mainly lim-ited to the case of single beams.However,in inertial confinement fusion,multiple laser beams are simultaneously incident into the target chamber,so that there is inevitably a region where multiple beams overlap in the target chamber.Recent studies have found that there are many new physical phenomena in multi-beam interactions.Multi-beam SRS demonstrates many different physical properties from those of single-beam SRS.I have carried out research on the Raman amplification process in the multibeam-plasma interaction.The main works are as the following:(1)A particle-in-cell simulation study is conducted on the four-wave mixing trans-mission amplification caused by three laser beams incident on a plasma.We found that the size of the four-wave mixing region has a positive correlation with the amplification of seed wave.It is observed that the seed wave can be amplified when the phase matching condition and the laser polarization condition are satisfied.This phenomenon of energy transfer between lasers may affect the uniformity of irradiation in fusion.Therefore it is necessary to suppress the scattered light generated by stimulated Raman scattering from interacting with other waves to reduce energy transfer.(2)The Raman amplification generated by multiple pumps with a symmetric config-uration distributed into the plasma has been studied.It is shown that when multi-beams are used for Raman amplification,the mutual coupling between the coherent pumps pro-duces a plasma grating.The grating grows with time and may affect the effect of Raman amplification,making the amplification effect lower than expected.If the grating forma-tion time can be reasonably controlled,the effect of multi-beam Raman amplification can be effectively enhanced.