缺陷诱导熔石英光学元件紫外激光损伤机制的正电子湮没研究

In the effect of high fluence UV laser irradiation, surface damage to the fused silica optics seriously limits the high fluence output of high power solid laser devices. Surface damage is closely related to the microstructure of fused silica optics, such as surface/subsurface defects and scratches and so on. To study the structure defects and the influence of structure defects on UV laser damage resistance properties of the fused silica optics are helpful to the modification research of fused silica. Positron annihilation technique is a non-destructive probe, which is sensitive to atomic size defects of materials. In this project, we pretreat fused silica optics by laser irradiation pretreatment and wet chemical etching pretreatment. Then we use positron annihilation technique, combined with conventional structure characterization techniques, to investigate microstructure defects of fused silica. We are committed to study the influence of defects on UV laser damage resistance properties of fused silica optics, and explore the mechanism of defects induced fused silica UV laser damage. As a result, we optimize the methods of pretreatments and establish the relation between positron annihilation parameters and UV laser damage threshold. The researches of this project can provide scientific and theoretical supports for the modification studies of fused silica optics UV laser damage resistance properties.

熔石英光学元件在高通量紫外激光作用下的损伤问题严重限制高功率固体激光器的负载能力，它与元件表面/亚表面缺陷、划痕等微观结构密切相关。研究熔石英光学元件中的结构及缺陷特征，以及对熔石英抗紫外激光损伤性能的影响，有助于熔石英光学性能的改性研究。正电子湮没技术是对材料中原子尺度缺陷敏感的无损探测技术，本项目利用正电子湮没谱学技术，结合常规结构表征技术，对激光预处理和化学湿刻蚀预处理的熔石英微观结构及缺陷进行鉴别和表征，研究缺陷对熔石英抗紫外激光损伤性能的影响，探讨缺陷诱导熔石英光学元件紫外激光损伤的物理机制，优化预处理方法，确定正电子湮没参数和紫外激光损伤阈值的关联图像。通过本项目研究，为改进熔石英光学元件抗紫外激光损伤性能提供科学依据和理论指导。

熔石英光学元件的抗紫外激光损伤性能和表面/亚表面划痕、裂纹、微观缺陷等密切相关。本项目系统研究了不同处理方式（化学湿刻蚀、紫外激光辐照处理、CO2激光辐照处理以及气氛退火处理）对熔石英元件抗紫外激光损伤性能的影响，研究表明，动态化学湿刻蚀对阈值提升效果最好，而对于表面质量较差的熔石英元件，增加紫外激光辐照和CO2激光辐照预处理可进一步提升元件损伤性能，并且实验给出了各种处理方式的优化指导。借助于正电子湮没技术，对不同处理方式下熔石英微观缺陷分布进行了鉴别表征，研究了正电子湮没参数-微观缺陷-损伤性能之间的关联，关于缺陷诱导熔石英光学元件的激光损伤机制的研究取得了阶段性结果。结果表明，熔石英亚表面的微裂纹、划痕、点缺陷、沉积物、污染物的存在增加了熔石英材料对紫外激光的吸收，对阈值影响显著。不同处理方式提升阈值机制有所不同，化学刻蚀可通过剥除直接去除亚表面缺陷，提高激光损伤阈值；激光辐照处理的物理机制是将激光能量传递给熔石英，促使网格结构的重排来改变材料内部缺陷分布，导致表面百纳米深度范围内缺陷分布状态接近微米深度范围内亚表面缺陷的分布，从而有利于熔石英元件阈值提升；CO2激光表面辐照研究表明激光辐照致使表面百纳米深度材料结构致密化。此外，已有数据表明对于微米深度范围内，熔石英元件空洞浓度的增加及尺寸的缩小并不利于阈值提升。研究成果对理解熔石英光学元件的缺陷诱导紫外激光损伤机理及提升元件抗紫外激光损伤性能提供重要信息，具有科学指导意义。