熔石英三倍频激光损伤及表面修复技术研究
文献类型：学位论文
| 作者 | 方周 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 邵建达 |
| 关键词 | 熔石英 激光损伤 损伤机制 CO2激光修复 飞秒激光修复 |
| 其他题名 | Third-harmonic laser-induced damage and surface mitigation technology of fused silica |
| 中文摘要 | 熔石英元件具有良好的光学、热学、力学性能，广泛应用于高功率激光系统中。但是在高功率激光作用下，熔石英表面很容易发生损伤，而且损伤点在后续激光作用下会快速生长。熔石英的激光损伤严重限制了系统运行通量的提升，成为高功率激光系统发展的瓶颈问题。因此，研究激光作用下熔石英的激光损伤问题，对于阐释激光与材料相互作用的物理过程、以及探索提高熔石英元件抗激光损伤能力的途径，都具有非常重要的意义。本文围绕熔石英的激光损伤问题，分别从以下几个方面开展了研究工作： 系统研究了熔石英体材料及熔石英表面在三倍频激光作用下的损伤特性。发现熔石英表面的损伤阈值比体材料的损伤阈值低一个数量级，表明熔石英的表面结构是限制其抗激光损伤性能的关键因素；经过对比可以发现，熔石英体材料的丝状损伤、熔石英表面的坑状损伤及熔石英表面的损伤生长点都具有类似的损伤形貌--由中心熔融部分与边缘断裂部分组成，揭示了相同的损伤过程。 在损伤形貌分析基础上，采用“热爆炸”机制解释了熔石英的激光损伤过程，热效应导致材料的熔融破坏，而爆炸产生的冲击及机械作用导致材料的断裂破坏。熔石英的亚表面裂纹或初始损伤点，通过调制光强、降低材料机械强度及直接吸收等方式促进了材料对激光能量的吸收，是诱导熔石英“热爆炸”过程产生的直接原因。 分析研究了不同类型及尺寸的初始损伤点在后续多脉冲激光作用下的损伤生长特性，发现损伤点的生长阈值远低于初始损伤阈值，而且与损伤点尺寸存在明显依赖关系，损伤点的尺寸越大，生长阈值越低。通过对初始损伤点进一步分析，并且计算损伤点及不同修复结构对电场增强的影响，明确了去除损伤材料及优化结构是提高熔石英元件抗激光损伤生长性能的修复方向。 计算了不同尺寸的矩形、锥形及抛物形修复结构对光场调制及光束传输的影响，结果表明矩形结构造成的光场增强相对较小；对于锥形或者抛物形结构，结构侧壁与入射光束所成的角度以小于20°为宜；另外在保证完全去除损伤材料的前提下，修复结构的尺寸应尽可能小。 在CO2激光修复装置中引入在线成像系统，能够实时判断修复效果。通过探索修复工艺，明确了CO2激光单点辐照方式所能修复的最大损伤点横向尺寸为150μm，深度为4.5μm左右。 创新的采用飞秒激光将熔石英表面的损伤点加工修复成矩形结构，并且在修复后采用HF刻蚀处理，最终完全去除了再沉积物。横向尺寸300μm深度为10μm左右的损伤点经过飞秒激光修复后，修复点的生长阈值提高了一倍左右。通过比较分析损伤点与修复点的差异，揭示了损伤材料（包括裂纹和缺陷）的去除和物理结构的优化是熔石英抗激光损伤性能提升的原因。 |
| 英文摘要 | Fused silica is widely used in high power laser systems because of its excellent optical, thermal and mechanical properties. But fused silica is easily damaged under high fluence laser irradiation, and the damage site grows exponentially with subsequent laser pulse exposure. The laser-induced damage of fused silica, which is the key factor on determining the output power of laser system, becomes a significant deterrent to the high power laser system performance. Therefore, studies on laser-induced damage of fused silica have significant practical meanings, including elucidating the mechanism on laser interaction with fused silica, and exploring the pathways to improve the laser resistance of fused silica. In this dissertation, researches have been carried out on the following aspects: Third-harmonic laser-induced damage characteristics of fused silica were investigated. The laser-induced damage threshold (LIDT) of bulk fused silica was one order of magnitude higher than that of the surface fused silica, which reveals that the surface structure plays a key role in determining the damage performance of fused silica. In addition, by comparing the different types of damage morphology, we found that the “filamentary damage” of bulk fused silica, the initial crater damage and damage growth site of surface fused silica all shows a similar damage feature: consisting of the central molten region and the surrounding fractured parts. Based on the research of the laser-induced damage characteristics of fused silica, a simple “thermal explosion” model was adopted to explain the damage process of fused silica. The accompanied thermal effect resulted in the thermal molten damage; the mechanical action resulted in the fracture damage of fused silica. The subsurface crack or initial damage site could effectively absorb laser energy by a variety of ways, including modulate the laser light intensity; reduce the mechanical strength of the material and direct absorption. The absorption of laser energy led directly to the generating of thermal explosion process. The damage growth characteristics of the initial damage sites with different type and size were investigated. It’s found that the damage growth threshold of damage site was much lower than the initial damage threshold. And the larger size of the damage site, the lower growth threshold. Through the analysis of the initial damage site, and the calculation of the effect of rough damage site and different mitigation structures on electric field enhancement, it turned out that the removal of damaged material and the optimization of physical structure are probable methods to improve the laser damage performance of fused silica. The effect of rectangular, tapered and parabolic mitigation structures with different size to the light field modulation and laser beam propagation was calculated. Results showed that the rectangular structure causes a relatively small light field enhancement, the angle between the rectangular or tapered structure and laser beam should be less than 20°. Besides, under the prerequisite of completely removing the damage material, the size of mitigation structure should be as small as possible. The CO2 laser mitigation technology was monitored by an on-line imaging system aiming at making sure that the mitigation process is successful. The maximum size of the damage site that can be mitigated by CO2 laser single point irradiation was 150μm in diameter and in 4.5μm depth. Innovative femtosecond laser mitigation method was also developed to solve the damage growth problem on fused silica; HF etching process was then used to remove the redeposition material. The damage sites with about 300μm diameter and 10μm depth were mitigated by femtosecond laser, and damage test results showed that the growth threshold of the mitigation sites almost doubles. It revealed that the removal of damaged material and structure optimization contribute to the improvement of laser damage growth resistance of fused silica. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15915]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 方周. 熔石英三倍频激光损伤及表面修复技术研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
入库方式： OAI收割
来源：上海光学精密机械研究所
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。