Propagation Of Intense Laser Light In Ionizing-gases And Plasmas

In this paper, we theoretically study the propagation of intense laser light in ionizing gases and plasmas, which is one of the key issues of inertial confinement fusion (ICF) "fast ignitor" scheme, laser particle acceleration, X-ray lasers, and intense laser light long distance propagation in atmosphere. Firstly, the propagation of intense laser light in ionizing gases is analyzed including the ionization-modulation instability, the vectorial and nonparaxial effects, and the mechanism of laser energy loss. Secondly, we analyze the propagation of intense laser light in plasmas, and effects such as the weakly relativistic nonlinearity, the ponderomotive force and the wakefield are analyzed. This paper is orgnized as four chapters according to the contents and the results: chapter 1 is a survey, and the last three chapters mainly are introductions of the author's work.Chapter 1: The inertial confinement fusion (ICF) and laser fution "fast ignitor" scheme are introduced; and also, the physics of intense laser plasma is introduced.Chapter 2: The prpagation of intense laser light in ionizing gases is analyzed in this chapter. Starting from Maxwell's equations, the paraxial propagation equation of intense laser light in ionizing gases is derived and is analyzed by means of the source-dependent expantion (SDE) method. An equation governing the evolution of the laser beam redius is obtained, based on which we analyze the ionization-modulation (IM) instability. Then, a vectorial, nonparaxial propagation equation is established, and the mechanism of energy loss during the propagation is analyzed.Chapter 3: The effects of weakly relativistic nonlinearity of intense laser light propagating in plasmas is analyzed. Firtly, the laser envelope equation and the walefeild equation are derived from Maxwell's equations and the hydrodynamic equations for the relativistic cold electron fluid. The effects of relativistic self-focusing (RSF) and preformed plasma channel guiding are analyzed. However, the effect of RSF leads to the singularity of beam redius focused to zero with infinity laser intensity when the laser power is lagerthan a critical value in the absence of other effects. Then, we anlyze the effect of higher order relativistic nonlinearity (HOR) and find that this effect can arrest the singularity due to the effect of RSF. Compared with the effect of nonparaxial, the effect of HOR dominates. In the case of ultrashort laser pulse, the effect of finite pulse length is anlyzed, and self-steepening in the front of the pulse will occur when only relativistic nonlinearity is considered.Chapter 4: In this chapter, we derive the formula of ponderomotive force from Lorentz equation and analyze the effect of ponderomotive self-channeling (PSC) firstly. It is found that the effect of PSC enhances the effect of beam focusing. And a nonparaxial propagation equation including the effect of PSC is established. Finally, we study the effect of longitudinal wakefield in the propagation of intense laser in plasma and find that this effect leads to asymmetric self-phase modulation of the pulse.