真空环境下纳秒脉冲激光诱导光学薄膜的损伤研究
文献类型：学位论文
| 作者 | 凌秀兰 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 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 | 光学薄膜 激光诱导损伤 真空环境 有机污染 后处理 |
| 其他题名 | Nanosecond pulse laser induced damage of optical coatings in vacuum environments |
| 中文摘要 | 随着激光系统在真空和空间领域的广泛应用，大量的光学薄膜元件将工作在真空环境或者特殊气氛下。作为激光系统中的关键部件，光学薄膜是激光系统中非常重要而又最易损伤的薄弱环节。为此本文较系统的研究了在纳秒脉冲激光作用下光学薄膜在真空环境或特殊气氛下的损伤特性及损伤机制。具体来说有以下几个方面： 介绍了用于真空环境下光学薄膜损伤测量的实验系统，并对光学薄膜损伤测量的方法、损伤阈值的定义及损伤的判定进行了详细的讨论，为科学、客观、深入的研究真空环境下光学薄膜的损伤规律及损伤机理奠定了基础。 比较研究了电子束沉积的薄膜在大气环境和真空环境下的单脉冲及多脉冲损伤特性。结果显示相对于大气环境，电子束沉积的光学薄膜其真空环境下的损伤阈值降低，真空环境下的多脉冲累积损伤效应更加明显，真空环境下的损伤形貌也与大气环境下的损伤形貌有显著差异。研究了环境气氛和气压对真空环境下光学薄膜损伤的影响。结果显示在真空环境中存入少量的氮气、氧气、氦气后，薄膜的损伤阈值都得到不同程度的提高，但存入气体的种类及气压不同，损伤阈值与破斑形貌也不尽相同。 分析了真空环境中光学薄膜的本征损伤机制。首先通过有限元方法分析了气体热传导对真空环境下光学薄膜损伤的影响，分析表明气体热传导差异不是大气环境与真空环境损伤差异的原因。其次，建立了多孔薄膜的堆积密度与薄膜热导率的变化关系，从热力损伤过程及缺陷诱导损伤过程分析了电子束沉积的多孔薄膜真空过程中的本征损伤机制---由膜层堆积密度及折射率的变化诱导的膜层热导率的变化对损伤的影响关系。 研究了真空环境下有机污染诱导光学薄膜的损伤特性及机制。首先分析了不同的有机污染物以及不同的有机污染模式对真空环境下光学薄膜损伤的影响，结果显示不同的液相污染物在样品表面的吸附形态不同从而导致不同的损伤结果；不同的有机污染模式对膜层损伤有着不同的结果。其次分析了真空环境下长期的放气污染对薄膜损伤的影响，结果显示长期的放气污染导致薄膜损伤阈值极大的降低，缺陷与吸附污染物的相互耦合可能是有机污染诱导薄膜损伤阈值降低的原因。 研究了两种后处理方式---热退火及激光预处理对真空环境下光学薄膜损伤的影响。研究显示退火过程通过改善薄膜的光学特性、结构特性及应力特性，从而改善了真空环境下光学薄膜的抗激光损伤能力。不同环境下的激光预处理对光学薄膜的抗激光损伤有着截然不同的结果，真空环境下的激光预处理降低了薄膜真空环境中的损伤阈值，而大气环境下的激光预处理可以有效提高样品在真空环境下的抗激光损伤能力。 |
| 英文摘要 | Due to the wide application of laser systems in vacuum or space environments, many optical coatings will be used in vacuum environment or special atmosphere. Optical film, as a pivotal component, is a very important and most easily damaged section in laser systems. In this paper, laser-induced damage characteristics and mechanisms of optical coatings irradiated by the ns pulse laser were study systemically in vacuum environment or special atmosphere. More concretely speaking, it includes the following aspects: The experimental setup of the laser-induced damage in vacuum was introduced. Moreover, in order to scientifically, objectively and thoroughly investigate the regularities and mechanisms of laser-induced damage of optical coatings in vacuum, the test method of laser-induced damage, the definition of laser induced damage thresholds and the determination of laser-induced damage in vacuum environment were also discussed in detail. Characteristics of laser-induced damage of optical thin films deposited by e-beam evaporation under single and multi-pulse laser irradiation are comparatively investigated in vacuum and atmosphere environments. The results showed that compared to normal atmospheric conditions, optical thin films have a decreasing laser induced damage thresholds and a more obvious accumulation effect of multi-pulse laser irradiation. Moreover, the morphology of the damaged sites showed a particular difference in two conditions. Effects of environments and gas pressures on laser-induced damage of optical films were also investigated. It is found that in vacuum environment with a few N2, O2, He2, laser induced damage threshold of optical films all increased in different degree. However, different gas environments and gas pressure can result in different laser induced damage thresholds and damage morphology. The intrinsic damage mechanisms of optical thin films in vacuum environment were investigated. To begin with, based on the finite element method, the impact of gas heat conduction on the laser-induced damage in vacuum environment was analyzed. It is found that gas heat conduction has little influence on the difference of damage thresholds in two cases. Then, through establishing the changing relation between packing density and thermal conductivity of porous films, based on the thermal-mechanical damage and defect induced damage process, the intrinsic damage mechanisms of porous films in vacuum process (the dependency of the laser-induced damage on the thermal conductivity induced by the change of the packing density and refractive index) was analyzed. The damage characteristics and mechanisms of optical films induced by organic contaminations in vacuum were investigated. Firstly, the impact of the different organic contaminations and different contamination modes on the laser-induced damage of optical coatings in vacuum were analyzed. It is found that different liquid organic contaminations result in the different damage results due to the different adsorption forms on the surface of the samples. Different contamination modes also have different effects on laser-induced damage in vacuum. Secondly, the longtime impact of outgassing organic contamination in vacuum system on the damage characteristics of optical films was investigated. The results show that outgassing organic contamination existing in vacuum system for long time resulted in largely decreasing in the damage resistance of the coatings. The inter-coupling between defects and organic contaminations is probably attributed to the decrease of the laser-induced damage threshold induced by organic contaminations in vacuum. The impact of two post treatment methods on the damage characteristics of optical film in vacuum was investigated. Based on improving the optical properties, structural and stress characteristics, thermal annealing can enhance laser-induced damage resistance in vacuum environment. Laser conditioning in different environments have an entirely different effect on the laser-induced damage of optical films in vacuum. Laser conditioning in vacuum environments decreased the laser-induced damage thresholds (LIDT), while the same laser conditioning in atmosphere environments can effectively improve the damage resistance of optical films in vacuum environments. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15650]  |
| 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 | 凌秀兰. 真空环境下纳秒脉冲激光诱导光学薄膜的损伤研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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