摘 要

作为脉冲放大系统的重要光学元件之一，脉冲压缩光栅的衍射效率决定了光栅对激光能量的利用率以及激光系统所能获得的最大脉冲功率密度。然而由于金属固有的吸收损耗高，普通镀金光栅的抗激光损伤阈值往往较低。研究发现，在光栅金膜表面增加一层介质膜，可以使光栅在衍射效率降低较少的情况下，大大提高光栅的抗激光损伤能力。在介质膜材料固定的情况下，不同结构的光栅衍射效率有很大差别，因此，研究带保护层的脉冲压缩光栅的结构与衍射效率的关系具有极其重要的意义和价值。

本文应用多物理场耦合软件COMSOLMultiphysics对衍射光栅的激光辐照过程进行了模拟，了解了介质膜镀金光栅的衍射效率随光栅结构变化的规律。本文研究一种透明的介质膜覆盖在金属光栅表面，使其在衍射效率降低可以接受的范围内大幅度提高光栅的抗激光损伤阈值，这种介质膜材料本次实验定为二氧化硅。本文通过调整介质膜镀金光栅的介质层厚度、占宽比、光栅周期、激光入射角、金膜层厚度、光刻胶厚度等数据改变光栅的结构，计算这些数据改变时光栅衍射效率的变化情况，最终达到结构优化的目的。由于上述影响结构的因素较多，模拟情况太复杂，不利于直接达成结构优化的目的。本文通过控制变量法，分别模拟光栅周期和介质层厚度、光栅周期和占宽比、金膜厚度和光刻胶厚度变化时，衍射效率的变化情况。大大降低了模拟实验难度的同时，也便于得到更加精确的结构参数。

介质保护层的添加为提高镀金光栅的抗激光损伤能力提供了一个研究方向，通过该方法可在保证衍射效率的前提下有效提高光栅的抗激光损伤阈值。对于介质膜光栅结构的研究，有助于从光栅的材料选择、制备工艺、结构设计等方面着手提高光栅的衍射效率和损伤阈值。

关键词：镀金光栅；衍射效率；介质膜；激光脉冲

Abstract

As one of the important optical elements of the pulse amplification system, the diffraction efficiency of the pulse compression grating determines the utilization of the laser energy for the grating and the maximum pulse power density that can be obtained by the laser system. However, due to the inherent absorption of metal loss is high, ordinary gold-plated grating anti-laser damage threshold is often low. It is found that the addition of a layer of dielectric film on the surface of the grating gold film can greatly improve the anti - laser damage ability of the grating in the case of less reduction in diffraction efficiency. In the case of the dielectric film material, the grating diffraction efficiency of the different structures is very different. Therefore, it is of great significance and value to study the relationship between the structure of the pulse compression grating with the protective layer and the diffraction efficiency.

In this paper, the laser irradiation process of diffraction grating is simulated by COMSOL Multiphysics, and the diffraction efficiency of the grating of the dielectric film is studied. In this paper, a transparent dielectric film is coated on the surface of the metal grating to greatly improve the anti-laser damage threshold of the grating in the range where the diffraction efficiency is reduced. This dielectric film is experimented with silica. In this paper, the structure of the grating is changed by adjusting the thickness of the dielectric layer, the ratio of the aspect ratio, the grating period, the laser incident angle, the thickness of the gold film, the thickness of the photoresist and so on to calculate the change of the grating diffraction efficiency , And ultimately achieve the purpose of structural optimization. Because of the above factors, the simulation situation is too complicated, which is not conducive to the purpose of structural optimization. In this paper, the control method is used to simulate the grating period and the thickness of the dielectric layer, the grating period and the aspect ratio, the thickness of the gold film and the thickness of the photoresist. Greatly reducing the difficulty of simulation experiments at the same time, but also easy to get more accurate structural parameters.

The addition of the dielectric protective layer provides a research direction to improve the anti-laser damage ability of the gold-plated grating, which can effectively improve the anti-laser damage threshold of the grating under the premise of ensuring the diffraction efficiency. For the study of dielectric film grating structure, it is helpful to improve the diffraction efficiency and damage threshold of grating from the aspects of material selection, preparation process and structure design of grating.

Keywords：Dielectric film gold-plated grating; Diffraction efficiency; dielective layer; Laser pulse

目录

摘要 I

Abstract II

第一章 绪论 1

1.1课题背景与意义 1

1.1.1啁啾脉冲放大技术简介 1

1.1.2脉冲压缩光栅的性能要求 2

1.2介质膜光栅的结构和制备 3

1.2.1介质膜光栅的基本结构 3

1.2.2介质膜光栅的制备 3

1.3介质膜光栅的研究与应用 5

1.3.1 介质膜光栅的研究进展 5

1.3.2 介质膜光栅的应用 7

1.3.3 介质膜光栅的数值分析方法 7

1.4论文的主要工作 7

第二章 理论基础 9

2.1激光在介质中的传播 9

2.2 温度场的形成 12

第三章 介质膜镀金光栅的物理模型 13

3.1理论模型的建立 13

3.2参数设置 13

3.3边界设置 14

第四章 数值模拟计算结果及分析 16

4.1介质膜光栅电磁场分布 16

4.2影响衍射效率的物理量分析 16

4.2.1衍射效率与周期和保护层厚度的关系 17

4.2.2衍射效率与周期和占宽比的关系 18

4.2.3衍射效率与金膜厚度和光刻胶厚度的关系 19

4.2.4衍射效率与激光入射角的关系 20

4.2.5衍射效率与入射激光波长的关系 20

4.3最佳结构下光栅磁场分布 21

总结 23

参考文献 24

致谢 27

绪论

1.1课题背景与意义

1786年美国天文学家David Rittenhouse成功用细金属丝绕制出第一块衍射光栅^[1]，拉开了科学界深入研究衍射光栅的序幕，几百年来，衍射光栅已发展成为一种十分重要的光学器件，广泛应用于医学、通讯、光电信息处理等领域。衍射光栅分为透射光栅和反射光栅两种，其中反射光栅由一系列平行排列的在空间上形成周期性结构的金属条组成，由于某些金属对光的高反射效率，很多镀金光栅对光的衍射效率很高，理论衍射效率最高可达到95%，但是由于金属固有的吸收损耗较高，镀金光栅在高能量激光照射时温度会急剧升高，导致光栅结构发生毁灭性破坏，失去其衍射作用。随着高功率激光的发展，传统镀金光栅越来越不能满足技术发展的要求，一种高衍射效率、高抗激光损伤阈值的介质膜镀金光栅被提出，并得到了广泛关注和快速发展，介质膜镀金光栅的整体设计以及介质膜的设计、制备和性能分析成为一个重要的研究课题^[2]。

1.1.1啁啾脉冲放大技术简介

从激光技术产生开始，人们对它的研究和利用就是向着高能量和高功率的方向发展的，为了降低激光发生器的负荷，激光器发出的原始激光脉冲并不具备高能量高功率的特性，只有经过激光系统中提高脉冲激光输出能量和功率的环节，才能形成我们熟知的高能量高功率激光，而啁啾脉冲放大技术就是该环节的关键部分。啁啾脉冲放大系统原理图见图 1.1。