【作者】 杨毅松；

【导师】 张彬；

【作者基本信息】 四川大学 ， 光学， 2005， 硕士

【摘要】 在惯性约束聚变研究中,由于靶丸对短波长激光的吸收率高于长波长激光,且短波长激光超热电子少,因此,利用短波长激光作为辐照靶丸的注入激光。而获得短波长激光唯一行之有效的途径就是利用大口径KDP晶体的三次谐波转换效应对大型钕玻璃固体激光器输出的高功率激光进行三倍频转换,因此,高功率激光的三倍频技术已成为ICF驱动器必不可少的关键技术。此外,ICF靶场系统对激光焦斑分布也有非常严格的要求,不仅要求焦斑能量集中度高,而且焦斑主瓣的光强分布要尽可能均匀,旁瓣非常小。在惯性约束聚变研究中,三倍频光的光束质量和三倍频光的聚焦问题一直是科研人员关心的两个主要问题。为了满足ICF研究对三倍频系统和聚焦系统的要求,有必要深入研究影响三倍频光光束质量和聚焦焦斑的主要物理因素。本文围绕三倍频光光束质量和聚焦问题开展研究工作,主要内容包括以下几个方面: 一、在耦合波方程基础上,建立了较为全面的三倍频转换物理模型,主要考虑了近轴衍射、离散效应、非线性效应、晶体吸收以及位相扰动等多种物理因素。编制了三倍频过程数值模拟程序和透镜聚焦模拟程序。 二、详细研究入射基频光的振幅调制和位相扰动、KDP晶体的非线性效应和光学元件的面形误差对三倍频光光束质量的影响。 三、建立了解决激光谐波转换逆问题(即由物理实验要求的三倍频光光束质量来确定对基频光光束质量和倍频晶体加工精度的要求)的物理模更多还原

【Abstract】 In the research of Inertial Confinement Fusion (ICF), the short-wavelength laser is usually used, because it can be absorbed by fusion target more efficiently than long-wavelength laser. At present, the only accessible way to obtain high-power short-wavelength laser in high-power solid-state laser is the third harmonic generation of large-aperture KDP crystal. Therefore, third harmonic generation of high-power laser is a critical technology in ICF. In addition, the distribution of focal spot is not only required to be with high power, but also with uniform central spot and little side lobes. Consequently, the beam quality and focal characterization of the tripling field are two important problems in the research of ICF. In order to satisfy the requirement of ICF on third harmonic converter, it is necessary to study on the physical factors affecting the beam quality and focal characterization of the tripling field. This thesis focuses on the beam quality and focal characterization of high-power tripling field. The main results obtained here can be summarized as follows:1. The general physical model of third harmonic generation has been built up on the basis of the coupling equation, which includes paraxial diffraction, walk-off, nonlinear interaction, the absorption of crystal, and the variation of phase. In addition, the numerical simulation code of third harmonic conversion and focus of high-power laser has been built up.2. Some physical factors affecting the beam quality of third harmonic, such as the variation of amplitude and phase of input fundamental field,nonlinear effect of KDP crystal and the fabrication quality of optical elements, has been studied in detail.3. The method for solving the inverse problem of harmonics generation has been proposed, namely, to determine the characterization of input fundamental field and the requirement for KDP from the required characterization of output tripling field. By using successive iteration method, the inverse problems of the type I angle-detuning scheme for double harmonics generation and the type I/II angle-detuning scheme for third harmonics generation have been solved numerically.4. The model of wavefront phase perturbation has been built up, where the random phase screen characterized by RMS Gradient and the random phase perturbation have been introduced to describe the low and the high frequency phase noise, respectively. Taking the type I/II angle-detuning scheme for third harmonics generation as an example, the influence of low-frequency phase perturbation and the high-frequency phase noise on the focal characterization of the tripling field has been studied. Furthermore, some technologies were summarized for controlling the beam quality and focal characterization of high-power laser beams.更多还原