Theoretical Investigation Of Intense Laser Modulation Instability

Self-focusing is one of the fundamental problems in Nonlinear Optics. It has always been a hot topic since the naissance of nonlinear optics. In high-power solid-state lasers, self-focusing is the major factor for degradation of laser beam and limits the maximum laser power available. As stated in Lowrence Livermore National Laboratory (LLNL) reports, self-focusing, especially small-scale self-focusing, has always been a significant problem in the total design, engineering development, and safe operation of fusion lasers. Therefore, self-focusing is of very important significance, both theoretically and practically. The paper is composed of 4 chapters: chapter 1 is a survey, chapter 2,3 introduced my parting work in the graduate career.In chapter 1, we introduce the meaning and the history of the study about modulation instability.In chapter 2, we discuss the optics self-focusing in beam propagation. The early research was based on the scalar approximation and paraxial approximation. To deal with the case of 2 dimension spatial self-focusing, it predicts the catastrophic collapse of a self-focusing beam in a Kerr medium. This un-physical collapse is due to the invalidity of the paraxial wave equation in the neighborhood of a self-focus. When the beam is thin enough that the width can be compared with the wavelength, we must consider the vectorial and non-paraxial effects. The conclusion is that the vectorial effect influences more on the small-scale self-focusing than the non-paraxial effect. A new growing mode existing when the modulation on the direction of polarization is discussed in this chapter.In chapter 3, spatiotemporal instability of ultrashort pulses results from the interplay among diffraction, group-velocity dispersins and nonlinearity. We use the model proposed by Brebec et al., for ultrashort pulsed beam propagation, to study the spatiotemporal instability. Consider the time delayed response, a new instability region appeares. The position of this region and the magnitude of the gain depend on the characteristic Raman response time. Self-steepen influence the gain of Stocks and anti-Stokes light to different extent.In chapter 4, we summering the contents of the paper.