Research On Beam Self-focusing In Interaction Of Intense Laser And Plasmas

When the intense laser(with power density≥1012W/cm2)interacts with the substance,the substance will be ionized into the plasma,which appears as a laser-plasma interaction(LFI).In the process of LPI,a large number of nonlinear phenomena such as self-focusing,filamentation,Stimulated Raman Scattering(SRS),and Stimulated Brillouin Scattering(SBS)will occur.With the advancement of laser technology,the nonlinear effects on laser-plasma interaction are getting deeper and deeper.Among them self-focusing has become a focused research in the field of high temperature and high density plasma de to the large variety of formations,diverse formation mechanisms,and significant impacts on current major projects such as laser inertial confinement fusion,fast ignition,and laser particle acceleration.This paper adopted the high-temperature and high-density plasma formed by the interactioa in intense laser(wiih power uensity>1012W/cm2)and matter as the research system.Based on the theoretical systems in the fields of plasma physics,electromagnetic theory,and fluid mechanics,the main methods of paraxial theory,higher-order paraxial theory,WKB approximation,and numerical simulation etc.have been used to study the self-focusing in the interaction of intense laser and plasma.The research focused on the formation mechanisms,the general principle,and the influential factors of self-focusing,the work of which mainly based on self-fousing in different plasma systems in the determination of ponderomotive force,relativistic nonlinearity factors,and collisional nonlinearity effects.The specific content includes thefollowing parts:(1)Considering the ponderomotive force,and applying non-paraxial ray theory and WKB approximation,the abnormal splitted ring formation during the course offilamentation in laser-plasma interaction has been studied.(2)Taking the theory of interaction in relativistic laser with exponential decay underdense inhomogeneous plasma and plasma with periodical density ripple as theresearch system,the theory of laser propagation in plasma has been discussed.(3)Based on the interaction system between intense relativistic laser and plasma,the laser beam filamentation and filamentation instability in the ultra-relativisticlaser-plasma interaction has been researched.(4)The hydrodynamics with combining plasma physics and electromagnetic theory have been adopted to study the self-focusing in collisional plasma with periodical density ripple.The comprehensive results have shown that,in the laser-plasma interaction system,the laser beam will produce many phenomena as filamentation,abnormal splitted ring,relativistic self-focusing and others,the changes of the off-axial component will cause the formation and variation of abnormal splitted ring.In exponential decay underdense inhomogeneous plasma,the intensity of self-focusing keeps relatively steady,while in plasma with periodical density ripple,the distribution of which presents quasi-periodic variation.Plasma inhomogeneity influences beam filamentation and filamentation instability as well.Under the combined effect of collision nonlinearity and periodical density ripple,three nonlinear phenomena of laser occur in turn which are stable self-focusing,self-defocusing and oscillational self-focusing.The study of the paper on self-focusing theoretically enriches the self-focusing physics in the laser-plasma interaction,and also provides a useful reference for the effective control of self-focusing in experiments such as ICF and laser particle acceleration.