Propagation Characteristics Of Laser Pulse In Inhomogeneous Plasma

The interaction between laser and plasma has always been a research hotspot.When the laser pulse propagates in the plasma,the various complex nonlinear interactions will occur,and abundant physical phenomena will be produced.Such as the relativistic self-focusing,plasma channel,laser wake excitation,self phase modulation,and hose instability.These complex phenomena make the laser plasma have important application value in the inertial confinement fusion fast ignition scheme,soft X-ray generation,high-order harmonic generation,laser wake acceleration and new light source.After many years of development,great progress has been made in theoretical and experimental studies on the propagation of intense laser pulse in homogeneous plasma.It is found that when the laser power is higher than the threshold power,the laser pulse can maintain stable propagation in a certain range of plasma density.The stable propagation of laser pulse plays an important role in the process of electron self-injection and acceleration,which plays an important role in particle acceleration and fusion in the future.However,there is little research on the propagation characteristics of intense laser pulse in inhomogeneous plasma.Therefore,this paper mainly studies the propagation characteristics of laser pulse in inhomogeneous plasma.The influence of laser pulsewidth,plasma density and plasma density distribution type on laser characteristics are discussed in detail.We briefly introduce the development of laser technology,the basis of plasma and the hot issues of laser plasma interaction in the chapter 1.In the chapter 2,we discuss the propagation characteristics of relativistic long pulse laser in inhomogeneous plasma.Based on the Maxwell equations and cold plasma equations,we obtain the Lagrange equation of the system by using Hamiltonian principle,and discuss the propagation of relativistic long pulse laser in homogeneous and inhomogeneous plasma.We study the propagation characteristics of long pulse laser in inhomogeneous plasma by numerical method.The results show that the change of laser pulsewidth does not affect the change of laser intensity and spatial distribution when the long pulse laser propagates in homogeneous plasma.Correspondingly,the distribution of electron density is unchanged.However,the intensity of laser pulse and the spatial distribution of electron density can be adjusted by modulating the plasma frequency.In the inhomogeneous plasma with Gaussian density distribution,the intensity of the long pulse laser is enhanced gradually as the increase of the amplitude of the Gaussian density distribution,and the transverse distribution of the laser pulse gradually appears a sharp distribution.In the inhomogeneous plasma with inverse Gaussian density distribution,the intensity of the long pulse laser decreases gradually with the decrease of the amplitude of inverse Gaussian density distribution,and the transverse distribution of laser pulse appears a platform distribution.Hence,the inhomogeneity of plasma has a significant effect on the propagation of long pulse laser.The amplitude and width of Gaussian and inverse Gaussian density distribution plays an important role in modulating the intensity and spatial distribution of laser pulse.In the chapter 3,we discuss the propagation characteristics of relativistic ultrashort laser pulse in inhomogeneous plasma.Based on Maxwell equations and cold plasma equations,we obtain the Lagrange equation of the system by using Hamiltonian principle,and discuss the propagation of relativistic ultrashort laser pulse in homogeneous and inhomogeneous plasmas.We study the propagation characteristics of ultrashort laser pulse in inhomogeneous plasma by numerical method.It is find that the stable propagation of relativistic ultrashort laser pulse in homogeneous plasma can be realized,and the intensity of laser pulse and the spatial distribution of electron density can be modulated by adjusting the pulsewidth of the incident laser and the plasma frequency.More interestingly,in the inhomogeneous plasma with density ripple,when the wave amplitude of density ripple is less than a critical value,the intensity of laser pulse is almost unchanged,the propagation characteristics of laser in the inhomogeneous plasma are basically consistent with that in the homogeneous plasma.However,when the wave amplitude of the density ripple is larger than the critical value,the inhomogeneity of the plasma has an obvious effect on the laser characteristics,and the intensity and the spatial distribution of the laser pulse will be modulated by the plasma density ripple.Finally,the work of this thesis is summarized and the research prospect in this field is prospected.