Investigation Of Propagation Characteristics Of Laser Beam

The background of this paper bases on the fast ignition in Inertial Confinement Fusion(ICF). In the thesis, the propagation characteristic of the laser beam through plasma and free space is investigated theoretically. The analytical expressions of the parameters of the laser beam such as the beam width and the beam quality factor are obtained and the main influence on the parameter is illustrated.Chapter 1: A simple survey of the development of fast ignition in inertial confinement fusion is made. The model and the principle of the several schemes on fast ignition are introduced. At the same time we make an analysis of the feasible and the merit and the defect of these schemes, and review the requires of fast ignition on the beam quality, and summarize the basic research methods of the propagation of laser beam.Chapter 2: The beam propagation of X-ray in an inhomogeneous plasma with a continuous varied refractive index is studied. We emphasize, theoretically and numerically, on the analysis of the effect of refractive index gradient on the beam parameters. The results show that the higher is electron density distribution, the effect is more evident. So the gradient effect must be included to measure higher density plasma in experiment.Chapter 3: In this chapter, the propagation characteristic and focusing properties of elegant Hermite-Cosh-Gaussian (EHChG) beam through a finite aperture are investigated. The variance of the beam width, the generalized analytical expression of MG2-factor and the power fraction of the truncated beam are derived theoretically and illustrated numerically. An analygis of the effect on the beam parametes and its varied trend is made.Chapter 4: The paraxial propagation of partially coherent beams with the Hermite-Gaussian mode is investigated. The more generalized and simple expressions of the mean squared width and the beam quality factor of the beam withdifferent mode order are obtained in terms of the cross-spectral density. Our re-sults show that the higher order strengthens the variations of the mean beam width and the beam quality factor for partially coherent beams, and the relation between the two parameters of partially coherent beams is independent of the coherence length.