摘 要

介质膜光栅作为一种重要的光学元件，现在已经广泛的应用到包括大型激光设施、光通讯、光信息处理、光存储、光电技术转换等领域。随着科学技术的不断进步，特别是大型激光系统的快速发展，对介质膜光栅的性能要求也越来越高。性能优秀的介质膜光栅不仅要具有良好的衍射效率，更要具备高的激光损伤阈值。

本文借助数值模拟软件COMSOL Mutiphysics 5.0首先针对介质膜光栅在激光辐照下的电磁场、温度场及应力场进行了数值模拟；然后在不同位置引入不同大小的杂质颗粒，杂质位置分为光栅内部及光栅表面两类，分析了杂质位置及尺寸对于介质膜光栅激光损伤阈值的影响；最后改变激光输出脉宽，探讨了不同脉宽下杂质对介质膜光栅激光损伤阈值的影响。

研究结果表明：位于强电磁场区域的杂质对于介质膜光栅激光损伤阈值的影响最大。随着杂质半径的增大以及脉宽的减小，杂质对介质膜光栅激光损伤阈值的影响加强。本文研究取得的结果对于大型激光设施的搭建，以及光通讯等领域的发展具有重要的指导意义。

关键词：杂质；介质膜光栅；激光损伤阈值；数值模拟；

Abstract

As a kind of important optical element, dielectric film grating has been widely used in areas including large laser facilities, optical communication, optical information processing, optical storage, photoelectric technology conversion and so on. With the continuous progress of science and technology, especially the rapid development of large-scale laser system, the performance requirements of the dielectric film grating is also getting higher and higher. Excellent performance of the dielectric film grating not only to have a good diffraction efficiency, but also have a high laser damage threshold.

In this paper, numerical simulation software COMSOL mutiphysicis 5.0 is used to simulate the electromagnetic field, temperature field and stress field of the dielectric film grating under laser irradiation. Then, impurity particles of different sizes are introduced at different positions. The impurity locations are divided into gratings and gratings The effects of impurity location and size on the laser damage threshold of the dielectric film grating were analyzed. Finally, the pulse width of the laser output was changed, and the influence of the impurity at different pulse width on the laser damage threshold of the dielectric film grating was discussed.

The results show that the impurity in the region of strong electromagnetic field has the greatest influence on the laser damage threshold of the dielectric film grating. With the increase of impurity radius and the decrease of pulse width, the effect of impurity on the laser damage threshold of dielectric film grating is strengthened.The results obtained in this paper are of great significance to the development of large-scale laser facilities and the development of optical communication.

Key Words：Impurity; Dielectric film gratings; Laser damage threshold; Numerical simulation;

目 录

第1章 绪论 1

1.1 课题的研究背景 1

1.2 介质膜光栅的激光损伤阈值 2

1.2.1多层介质膜的激光损伤阈值 2

1.2.2 浮雕结构引起的损伤 4

1.3 课题主要工作 4

第2章理论基础 5

2.1电磁场理论 5

2.2 热传导方程 6

2.3热应力场理论 6

第3章介质膜光栅的场分布模拟 8

3.1 介质膜光栅模型设计 8

3.1.1光栅模型的建立 8

3.1.2参数的设定 9

3.1.3 网格的划分 9

3.1.4边界条件的设定 10

3.2引入杂质前介质膜光栅场分布模拟 11

3.2.1介质膜光栅电磁场分布模拟 11

3.2.2介质膜光栅温度场分布模拟 12

3.2.3介质膜光栅应力场分布模拟 13

3.3 介质膜光栅杂质颗粒的场分布模拟 14

3.3.1杂质位置对介质膜光栅场分布影响研究 14

3.3.2杂质半径对介质膜光栅场分布影响研究 19

3.3.3激光输出脉宽对介质膜光栅场分布影响研究 22

第4章全文总结 26

参考文献 27

致谢 29

第1章 绪论

1.1 课题的研究背景

啁啾脉冲放大技术是先将超短激光脉冲展宽，再将激光能量放大，最后用脉冲压缩光栅将激光脉冲压缩成高功率高能量的超短激光脉冲的一项技术^[1]。自从这项技术被斯特里克兰提出后^[2],人们建立了很多超高强度的大型激光设施,如OMEGA-EP,LIL petawatt，LULI- 2000等^[3]。而作为啁啾脉冲放大系统的关键光学器件^[4],脉冲压缩光栅必须具有高的衍射效率和高的激光损伤阈值。特别是最后一个光栅，通常是啁啾脉冲放大系统中抗损伤能力最小却最昂贵的光学元件^[5]。传统的脉冲压缩光栅为金属光栅。虽然金属光栅有很高的衍射效率，理论上能够超过95%^[6]，但是由于金属材料的本征吸收损耗，金属光栅的激光损伤阈值很低，从而限制了它的发展。因此，Perry在1995年提出了多层介质膜光栅（MDG）概念^[7]。介质膜光栅采用电介质材料作为薄膜材料，由于电介质材料透明，其本征吸收接近于零，因此电介质材料的激光损伤阈值要远远高于金属材料。在衍射效率方面，通过多层膜的干涉作用可以使其获得较高的反射率，而在介质膜表面刻蚀形成浮雕结构后也可使其衍射效率大大提高^[8]。因此，介质膜光栅完全可以满足在高功率激光系统中对脉冲压缩光栅衍射效率和激光损伤阈值的要求^[9-11]。

介质膜光栅不仅可以应用到啁啾脉冲放大系统中，还可以应用于光通讯、光信息处理、光存储、光电技术转换等领域，比如在光开关和光分配系统中可以作为选择分束器、反射器、滤波器和偏振分束器等^[12-13]。同时，应用介质膜光栅的超快激光系统在医学，生物学，计量学和材料处理等领域也引起了人们极大的兴趣^[14]。作为一种重要的光学元件，介质膜光栅也被广泛应用于军事领域，对于我国国防实力的提高具有重要的意义。