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题名	紫外激光薄膜损伤特性研究
作者	于振坤
学位类别	博士
答辩日期	2014
授予单位	中国科学院上海光学精密机械研究所
导师	贺洪波
关键词	介质膜，紫外纳秒激光诱导损伤，缺陷
其他题名	Laser induced damage of ultraviolet optical coatings
中文摘要	随着激光系统能量的不断提高，光学元件表面需要承受的激光辐照强度也随之增强。光学元件，尤其是紫外薄膜元件的损伤问题日益严重。光学薄膜作为激光系统中不可或缺的产品，成为限制激光系统发展的短板。研究薄膜在紫外纳秒激光（355 nm）辐照下的损伤情况，成为当前紫外激光系统相关科研人员研究的重点。本文基于对强激光薄膜材料的基本物理化学性能、激光技术、薄膜制备工艺、薄膜与激光相互作用过程等内容的深入研究，结合大量的激光与材料（薄膜元件）相互作用实验，给出材料本征参数、薄膜制备工艺对元件损伤性能的半定量影响，为紫外激光薄膜的研制提供技术支持。具体工作如下： 研究了几种块体材料（晶体材料和玻璃态材料）紫外激光辐照下的损伤特性。根据材料的带隙以及Franz-Keldysh效应描述其损伤阈值与带隙大小的关系。根据这个关系可以半定量描述薄膜材料损伤阈值的极限范围。同时，对一些材料的体损伤阈值可以进行预测。 研究薄膜抗激光损伤性能与沉积工艺之间的关系：薄膜抗激光损伤能力与镀膜过程中多种因素密切相关，薄膜态材料的损伤阈值要远低于对应块体材料的损伤阈值。另外，缺陷（杂质缺陷，能级缺陷）是造成紫外纳秒激光作用下损伤阈值下降的主要因素。实验发现薄膜损伤阈值受到基底加工、基底缺陷分布状态影响。同时，在研究薄膜热学破坏的同时，分析了薄膜的力学性质对损伤阈值的影响，并利用薄膜应力公式半定量的描述一定条件下薄膜损伤阈值与其应力的变化关系。 实验发现紫外纳秒激光作用下，HfO2薄膜损伤过程中存在多缺陷耦合效应。根据薄膜应力关系和缺陷温升模型证实多缺陷在薄膜损伤过程中具有耦合效应，该效应可以显著降低薄膜的损伤阈值。 利用第一性原理计算了薄膜态材料的性质，结合实验中存在的组合膜系（氧化物、氟化物）在氟氧化物的界面容易发生损伤问题，证明氟氧化物界面由于氧原子的迁移，容易形成氟氧化物，降低材料的带隙，从而降低薄膜的损伤阈值。
英文摘要	Laser-induced damage to optical thin film coatings has been a limiting factor in the development of high-power laser systems, especially the ultraviolet laser system. Damage behavior of optical thin film coatings under the nanosecond pulse laser has been extensively studied. However, researchers still encounter several problems. In this work, based on the physical and chemical properties of coating materials, bulk and coating damage experiments, interaction model of laser and matter, we investigated the relationship between the properties and the damage resistance of bulk and coating materials. The detail of our work is listed as followings: The laser damage resistance of bulk materials (crystals and fused silica) irradiated at the ultraviolet laser has been investigated experimentally and theoretically. The results show band gaps have the main responsibility for the laser induced damage threshold of bulk materials. According to the Franz-Keldysh effect, an empirical law can interpret the relationship between band gap and damage threshold of bulk materials. This empirical law can also be extended to other materials. Generally, the damage threshold of coatings is lower than that of bulk materials. As for coatings damage, the defects (impurities and defect levels) rapidly decreased the damage threshold. Due to the polished process and defects distribution of substrate, the damage threshold of coatings can hardly describe the intrinsic damage threshold of corresponding coating material. Besides, the stress plays a great role in the damage process of coatings. Furthermore, we have developed an analytical model to predict the relationship between the stress and the damage threshold of coatings. Our model can capture the trend of threshold as a function of stress, and show that we can improve threshold by adjusting the stress in the film. Coupling effect of defects is observed during the laser induced damage process (HfO2). A theoretical model based on the thermal transfer and stress is proposed to describe this coupling effect. Moreover, it proves this effect decrease the damage threshold of coatings. The development of fluoride/oxide double stack coatings presents a promising future for the high laser damage resistance under ultraviolet laser irradiation. However, the damage resistance is still weaker than that of fluoride coatings. High absorption defects are found at the interface of fluoride and oxide. These defects are originated from the couple effect of fluoride and oxide layers. The oxyfluorides are the main reason behind the dropped damage resistance. We use the first principle theory to simulate this process and experiments demonstrate high absorption defects appear at the interface of fluoride and oxide.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15858]
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	于振坤. 紫外激光薄膜损伤特性研究[D]. 中国科学院上海光学精密机械研究所. 2014.

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