The Study Of The Wide-band Pulsed Beams Propagation And Small-scale Self-focusing Properties

Small-scale self-focusing is one of the major factors to restrict the capability and efficiency of high power laser drives. People always take many measures to restrain small-scale self-focusing, and enhance laser beam quality. With the rapid advances of laser driver technology in inertial confinement fusion (ICF), wide-band pulsed beams were applied in high power laser system gradually. In wide-band pulsed light beams propagation, generally speaking, small-scale self-focusing was restrained preferably. And the bandwidth of wide-band pulsed beams leads to many new questions. Therefore the study of wide-band pulsed beams has been a focus of the scientific research.In this thesis, the propagation of the wide-band pulsed beams was studied by theoretical method and the numerical simulation. The thesis is composed of 5 chapters, among which are, Chapter 1 is a survey, Chapter 2, 3, 4 are the introductions of our own work, and Chapter 5 is a conclusion. The thesis is structured particularly as follows.Chapter I: The inertial confinement fusion (ICF) and laser fution "fast ignitor" scheme are introduced; and also, the wide-band pulsed beam is introduced.Chapter 2: Base on the linear stability theory, a linear model is used to analyze the influence of the air gap between slabs on small-scale self-focusing modulation growth in the slab amplifier. The quantitative relations between B-integral, the number of slabs, and modulation gain spectrum are given explicitly. The change law of modulation growth with B-integral and the number of slabs has been discussed theoretically. And the approximative gain spectrum is given with equivalent power and equivalent B-integral.Chapter 3: The basics equations for the wide-band chirped pulsed beam propagation are introduced. We discussed the spatial instabilities of the wide-band pulsed beam propagation. The large chirp item was calculated separately, which simplified the numerical simulation. The changes of the spatial instabilities with bandwidth have been analyzed theoretically. The conclusion ignored Group Velocity Dispersion (GVD) was not agree with the result of simulation, so we can't ignore the influence of GVD of the wide-band pulsed beam propagation.Chapter 4: The spatiotemporal instabilities of wide-band pulsed beam propagation were discussed. We analyzed the changes of the spatiotemporal instabilities withbandwidth, B-integral and GVD parameter β₂ theoretically. β₂ is not an ignorableparameter for the wide-band pulsed beam propagation. The bandwidth and B-integral will influence the modulation flux evidently all. Chapter 5: Summarizing the contents of the thesis.