缺陷诱导透射元件激光损伤行为的纳秒时间分辨和诱因诊断

The laser induced damage of transmission elements which are basic components in high power laser facility, is becoming a limiting factor for the further development of high power laser technique. Even absorbing defect or inner crack hiding in several micrometers and to a few dozen micrometers beneath the top surface, is probably able to induce damage to the transmission elements in ultraviolet band. Besides, its extremely small size and disordered state make impossible taking conventional detection. Therefore, the diagnosis of factors limiting damage performance improvement is a key technique for improving the fabrication technology of optical elements. Focused on the laser damage of third harmonic transmission elements, using pump-probe detecting and imaging technique, the project is on the characteristics and growth law of the initial destructive structure induced by defects during laser irradiation at nanosecond scale. According to the differences of damage behaviors a variety of defects lead to, we propose a new method, which is able to find out the absorbency and constitutive property of the damage inducement, and to discriminate the depth position with sub-micron precision. In addition, the project is trying to be technique support for breakthrough on research and development of the third harmonic transmission elements, by statistically analyzing characteristics and depth position of various limiting defects introduced by different grinding and polishing approaches as well as performance influence these defects make to actual sample to optimize the fabrication process of grinding and polishing.

透射光学元件是高功率激光装置中必不可少的基本元件，其激光诱导破坏问题已成为制约强激光技术进一步发展的关键因素。即使在表面以下几微米到几十微米区域隐藏的纳米尺度的吸收性缺陷和内部裂纹，都可能成为透射元件紫外波段损伤的诱因和限制性因素，而其尺度极小和无序分布的特点使常规检测方法难以识别和表征。因此，对限制损伤性能提升的诱因诊断是指导元件加工工艺改进的关键技术。本项目以三倍频透射元件为研究对象，利用纳秒时间分辨的泵浦探测成像技术，探索缺陷诱导激光损伤过程中初始破坏结构在纳秒时间尺度的特征和生长规律；依据不同类型缺陷诱导损伤行为的差异，提出一种能够对损伤源吸收性和结构性进行分辨、位置深度亚微米精度识别的损伤诱因诊断方法；统计性分析不同研磨和抛光工艺下引入的各种限制性缺陷的特征、位置深度，以及对实际样品损伤性能的影响，明确制备工艺的优化方向，为我国在研制三倍频透射元件上实现突破提供技术支撑。

三倍频激光辐照下透射光学元件的激光损伤一般由表面以下几微米到几十微米区域隐藏的吸收性缺陷或内部裂纹诱导，而其尺度极小和无序分布的特点使常规检测方法难以识别和表征。因此，本课题利用纳秒时间分辨的泵浦探测成像技术，研究了缺陷诱导激光损伤过程中初始破坏结构在纳秒时间尺度的特征和生长规律，以此发展了一种能够对损伤源位置深度微米精度识别的损伤诱因诊断方法。研究工作的开展基本上按照项目的研究计划和实施方案执行，完成了项目的研究内容和研究目标。主要取得了以下三方面的研究成果：（1）基于泵浦-探测技术，建立了微米空间分辨和纳秒时间分辨的成像系统，明确了缺陷诱导损伤行为的时域变化过程；（2）系统研究了不同类型缺陷的制备方法，缺陷诱导激光损伤特征的一致性和重复性评价，并依据不同类型缺陷诱导损伤行为的差异，提出了一种能够对损伤源位置深度微米精度识别的损伤诱因诊断方法；（3）统计性分析了光学元件发生损伤时损伤诱因的特征，包括位置深度、与能量关系、瞬态特征与最终深度及宽度、时间演化规律等信息，明确了泵浦探测成像技术对实际样品损伤诱因的识别和诊断能力。. 相关研究成果发表在Applied Optics、Optics & Laser Technology、Optical Engineering等SCI和EI检索文章6篇，同时还申请发明专利2项，软件著作权4项，参加国际会议1次。培养硕士研究生3名，毕业1名。