【作者】 郑一周；

【导师】 胡巍；

【作者基本信息】 华南师范大学 ， 光学， 2004， 硕士

【摘要】 自聚焦是非线性光学中的一个基本物理问题，自非线性光学诞生以来它一直是一个热门课题。在用于惯性约束核聚变(ICF)的高功率固体激光驱动器中，自聚焦是使光束质量变坏和限制输出功率的主要因素，正如美国劳仑斯·利弗莫尔国家实验室(LLNL)的报告所述，自聚焦，特别是小尺度自聚焦，是聚变激光器总体设计、工程研制和安全运行的重要问题。所以，研究自聚焦无论在理论上还是实际应用上都具有十分重要的意义。现在本文全文分三部分，第一章为概述，第二、三章介绍我硕士期间所作的工作，第四章是总结。 第一章：前言，介绍了调制不稳定性研究的意义和进展。 第二章：讨论光束传输的自聚焦。早期的自聚焦研究是在考虑了傍轴近似和标量场近似的前提下得到的。在该理论应用于空间二维的自聚焦时，出现了光束将无限聚焦的结果，这在物理上是不可想像的，原因是在自聚焦点附近傍轴方程已经失效了。因此，当光束十分细小时(如等于或小于波长时)，需要使用修正的公式。由Maxwell出发，通过量级分析的方法得到非傍轴和矢量的修正的传输方程。结果表明非傍轴和矢量效应都改变了自聚焦的强度和模式，而矢量效应的影响更强。同时与极化方向平行的新的增益模式有可能出现并可以在波长的尺度上产生自聚焦，文章讨论了这种可能性。 第三章：超短脉冲的时空不稳定性是衍射、群速度色散和自相位调制三者之间的相互作用导致的。本文采用了Brabec提出的超短脉冲传输模型，脉冲光束的时空的自聚焦行为变得十分复杂，不但原来的增益区间缩小了，而且在反常色散介质中会出现一个新的增益区间。对于超短脉冲而言，介质的响应也不能看做瞬时的，如果考虑拉曼效应产生的响应的延迟，会产生一对增益边带，其位置和大小由响应时间决定。自陡峭效应使斯托克斯和反斯托克斯光的增益大小不一样。 第四章：结束语，总结全文的工作。更多还原

【Abstract】 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.更多还原