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题名	激光薄膜耦合损伤问题研究
作者	孙卫
学位类别	硕士
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	齐红基
关键词	亚表面缺陷 电子束加热蒸发 溶胶-凝胶 激光诱导损伤阈值 损伤形貌
其他题名	The coupling damage effect of laser optical coatings
中文摘要	随着高功率激光技术的不断发展，激光器的输出功率越来越高，也就对光学元器件特别是光学薄膜元件提出了更高要求。光学薄膜元件是激光系统的核心元件，其抗激光损伤性能是影响光学系统稳定性和使用寿命的重要因素之一。通过基底清洗技术、膜系设计、沉积工艺、后处理工艺等系统优化，虽然已经有效地提高了薄膜的激光损伤阈值(LIDT)，但是其LIDT的进一步提高受到了限制。研究表明，激光薄膜损伤常常发生在薄膜与基底界面处，主要原因包括：1）亚表面缺陷在激光作用下存在局域场加强、力学性能下降、吸收增强等现象；2）基底与薄膜界面存在应力失配，界面污染等；3）基底缺陷及亚表面缺陷与薄膜界面耦合。由于基底缺陷及亚表面缺陷与薄膜的耦合作用对薄膜系统损伤行为有很大影响，本文着重研究基底界面固有缺陷，包括在1064nm纳秒激光辐照下的空白基底、电子束蒸发的SiO2单层膜和溶胶-凝胶SiO2单层膜。此外，利用三种不同的清洗方式手工擦洗、超声清洗和酸洗对界面固有缺陷进行调控。 对空白的熔石英基底而言，后表面更易损伤，且损伤斑呈现以缺陷为中心的同心圆环特征。利用SEM进一步分析，1064nm纳秒激光脉冲辐照下基底表面出现了与入射激光偏振方向垂直的周期性条纹结构，条纹周期在610nm-670nm之间，基本独立于入射能量关系，但周期性结构的深度随入射能量增加而增加。另外，再沉积层及亚表面缺陷的去除在一定程度上很有效的提高了基底的抗激光损伤阈值。基于损伤统计模型，系统分析了空白基底表面诱导缺陷的密度、缺陷阈值等信息。 采用电子束加热蒸发制备的SiO2单层膜，表面呈现以缺陷为中心的同心圆环特征。损伤斑的尺寸及深度随着辐照激光能量的增加近似呈现线性变化。借助于激光辐照下缺陷诱导等离子体区域上下界面对入射激光反射存在的干涉效应，初步解释了以缺陷为中心的同心圆环的成因。除此之外，基于缺陷诱导损伤的统计模型，系统分析了此类单层膜的缺陷密度和阈值信息。 溶胶-凝胶法制备的SiO2单层膜，抗激光损伤阈值要比物理膜的高很多，更接近于空白基底的LIDT，表明对于溶胶-凝胶膜而言由于其多孔结构，耦合效应弱。同样分析了溶胶-凝胶膜的损伤形貌，并将其与物理膜对比。基于缺陷诱导损伤统计模型，系统分析了溶胶-凝胶SiO2单层膜表面诱导缺陷的密度、缺陷阈值等信息。
英文摘要	With the development of high power laser technique, the laser output power is higher and higher, which also puts forward higher requirement on the optical component, especially optical coatings. Optical coatings are the important components of the laser system, and the laser damage resistance of optical coatings is one of the key factors influencing the stability and life time of high power laser system. With the optimizations of substrate cleaning, optical coating design, fabrication technique, post-treatment, the laser induced damage threshold (LIDT) of coatings has been effectively improved, but the further improvement of LIDT is limited. Researches show that the laser damage often happens at the interface between the coating and the substrate due to the following reasons: 1) the subsurface defects induced local field intensification, mechanics performance degradation, absorption enhancement; 2) the interface stress mismatch and interface pollutions; 3) the couple effect between the substrate defects and coatings. Because the couple effect between the substrate defects and the coating plays a great role in the damage of laser coatings, the research emphasis is placed on the intrinsic defects at the interface of substrate, including the bared substrates, e-beam evaporated SiO2 single layer, and sol-gel spinned SiO2 single layer with 1064nm nanosecond laser irradiation. Besides, three different cleaning methods, namely manual cleaning, ultrasonic cleaning, acid etching process are used to modulate the intrinsic defect at the interface. For the bared fused silica substrate, the exit surface is easier to be damaged and the typical damage morphology of the damage sites is some concentric rings centered on the local defects. Further analysis by SEM shows some periodic ripple structures on the surface of the substrate. The direction of the ripples is perpendicular to the incident laser field, the period of the ripples, ranging from 610nm to 670nm, is independent of the incident energy, but the depth of the ripple increases with the incident energy. Based on the statistical model of defect, the defect density and threshold of the bare substrates have been analyzed systemically. For electron beam evaporated SiO2 monolayer coatings, concentric rings centered on local defects were also observed on the surface of SiO2 monolayer. The size and depth of the damage sites increase linearly with the incident fluence. Based on the interference between the reflected laser irradiations at the air/ shock-front and shock-front/coating interface, a new mechanism is put forward to explain the concentric rings. Besides, the defect density and threshold of the SiO2 monolayer are analyzed systemically based on the statistical model of defect induced damage. For sol-gel spinned SiO2 monolayer coatings, the LIDT is higher than that of the PVD coatings, almost close to that of the bared substrates, which indicate the couple effect is weak for sog-gel coatings due to the porous microstructure. The damage morphology of the sol-gel coatings are also analyzed and compared with those of the SiO2 monolayer coatings prepared by electron beam evaporation. With the statistical model of defect induced damage, the defect density and threshold of the sol-gel SiO2 monolayer are also analyzed quantitaviely.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/16863]
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	孙卫. 激光薄膜耦合损伤问题研究[D]. 中国科学院上海光学精密机械研究所. 2014.

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