【作者】 张问辉；

【导师】 陈建国；

【作者基本信息】 四川大学 ， 光学， 2005， 硕士

【摘要】 在可靠运转的前提下,用于ICF研究的高功率激光系统(如美国利弗莫尔国家实验室点火装置NIF或者法国的LMJ等)的功率很高,从某种意义上说,系统元件的抗激光辐照能力的大小决定了系统的功率水平和运行性能。了解系统中元件的损伤机理,掌握所用材料的激光诱导损伤阈值(laser-induceddamage-threshold,简写为LIDT)对于强激光研究领域的科研人员和工程技术人员是非常重要的。由于影响激光损伤的因素众多,所涉及到的面也是极其丰富的,高功率激光诱导损伤至今仍然是一个讨论很热烈的问题。本文围绕激光损伤的三个核心问题—激光诱导光学元件损伤机理、LIDT测试和提高LIDT的激光预处理工艺开展研究工作,主要内容包含了以下几个方面: 一、阐述了ICF的发展对高功率激光损伤研究的需求。回顾了激光诱导损伤机理研究的历史,对激光损伤测量方法研究现状和损伤研究的复杂性进行了分析。 二、研究了激光与光学元件相互作用时的温度场,利用脉冲的周期性以及重复周期比脉宽大许多个数量级的特点,建立了激光系统稳定运行时,周期重复的短脉冲在用作窗口等的平板光学元件上造成的温度分布的物理模型。对热传输、元件的应力场计算、冲击波的形成以及电场分布跟元件损伤的关系进行了分析。 三、以光学中心根据ISO11254建立起来的损伤测试平台介绍了LIDT测量全部过程。对常用于损伤判断的光斑变形法、散射检测法等方法及其原理进更多还原

【Abstract】 The high power lasers for inertial confinement fusion such as National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) or the Laser Mega-Joule (LMJ) in France always work at extremely high power or energy. For some sense, the power level and the performance of the laser system are limited by the damage resistance of the components to intense laser illumination. Therefore, it is vital for the researchers and technicians working in high power laser area to get some knowledge about damage mechanisms or acquire the correct laser-induced-damage-threshold (LIDT) of the components. However, the laser-induced-damage in the optics is so complicated, for it is affects by lots of factors lying in physics or chemistry. It has been attracting the researchers’ attention since the first high power laser system come into application. For these reason, this thesis focus on some laser-induced-damage mechanisms, LIDT testing experiment and laser conditioning, which is a feasible technology to improve the LIDT. The main results obtained can be summarized as follows:1. The requirement for laser-induced-damage research in ICF has been expatiated. The investigation history of damage mechanisms and testing has been summarized. Meanwhile, the complexity of laser-induced damage researching has also been analyzed.2. Thermal, stress and electric field changing of some optics during the interaction with the laser have been studied. A physical model have been set up to calculating the temperature distribution of the optical components irradiated by the periodic pulses by making full use of the periodic characteristics of the pulsed lasersystem. Some methods to get the thermal transfer stress in components have been introduced. Relations between laser-induced-damage and the electric field changing and the formation of the shock-wave in optics have been analyzed.3. The whole LIDT testing process has been introduced based on the LIDT testing station which was built up regulated by the ISO 11254 standard in Chengdu Fine Optical Engineering Research Center. Some methods to identify the damage have been presented. These methods could be beam-distortion detecting, scatting probing and so on. Theories on these methods have also been given. Furthermore, damage test experiments have been set up to study the damage characteristics and mechanism of the color-separating gratings (CSGs) and silica irradiated by the 1064 nm and 355 nm laser respectively.4. The origins of the uncertainty of LIDT testing result have been completely deduced. An operable model to calculate the relative combined standard uncertainty of LIDT has been set up. As an example, it has been successfully applied to analysis the uncertainty of the LIDT of the 1064 nm HR thin-film sample.5. The laser conditioning method has been studied, which can extremely improve the LIDT of the optics, especially coatings. Methods of laser conditioning have been investigated, such as R-on-1, N-on-1, single-step off-line and 2-step laser conditioning process. Modes like modular benign ejections have been applied to explain the LIDT improvement by the laser conditioning. Finally, an experiment with 1064 nm Nd:YAG laser conditioning on HfO2/SiO2 coating samples has been set up to study the improvement effect of damage threshold.更多还原