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如图1所示为笔者课题组自主搭建的激光损伤阈值测试平台。为了得到与实际强光系统中损伤水平相当的熔石英损伤元件,使用该装置对熔石英元件进行强光打靶处理。选取一块材料为Heraeus 312、规格为50 mm×50 mm×10 mm的熔石英元件作为实验样品,元件表面粗糙度为0.975 nm,满足实际系统要求的表面粗糙度小于1 nm指标。使用波长为355 nm、调Q后脉宽为7 ns的脉冲激光通过光栅扫描路径辐照熔石英元件,制备损伤样件。激光输出能量均值65 mJ,1/e2光斑半径为0.5 cm,计算所得能量密度值约为8.28 J/cm2。
图2所示为磁流变修复光学元件过程。为深入揭示磁流变对熔石英元件小尺寸损伤的修复机理,使用自主研发的KDMRF-1000 F磁流变机床对熔石英损伤元件进行逐层修复实验,每次修复深度为1 μm,表1为磁流变其余工艺参数。实验中,磁流变修复损伤表面会产生明显的拖尾现象,破坏样件表面质量,因此在逐层去除过程中始终保持加工方向不变,以最大程度降低损伤向外扩散。在均匀去除实验中,直接观察样件可发现其表面有少量大尺寸损伤点,但无法观察到密集的小尺寸损伤点,使用超光滑表面激光散射缺陷检测仪检测,可观察到大量小尺寸损伤点。
表 1 磁流变工艺参数
Table 1. Magnetorheological process parameters
Parameter Rotation number/r·min−1 Rate of flow/L·min−1 Field current/
AIndentation depth/mm Value 260 120 8 0.2 -
多模态原位检测法是指针对同一位置同一对象的不同性能指标进行多项检测,相比传统的检测手段和思路,多模态检测法的相关性更强,检测更高效,评估更全面。多模态原位检测装置总体硬件结构设计如图3所示。多模态原位检测装置基于光热弱吸收检测、激光共聚焦显微检测、荧光显微检测和激光损伤测试四种检测表征技术组成,通过高精度运动平台对表面微区的固定位置进行原位检测。该装置设计引入激光损伤测试功能,但现阶段由于时间关系该功能暂未实装。该设备包括四个检测子系统和两个相关控制系统,分别为:光热显微成像子系统,激光共聚焦显微成像子系统,荧光显微成像子系统,激光损伤检测子系统,电控及信号采集子系统和软件子系统。基于逆向哈特曼和“以小拼大”的子孔径拼接测量原理,提出了一种逆向哈特曼阵列拼接测量新方法,如图4所示。首先将被测元件划分为若干相互重叠的子孔径,而后采用逆向哈特曼阵列测头分别测量各子孔径的斜率误差,最后利用各子孔径重叠区的冗余数据进行数据拼接,得到全口径斜率误差,并重构出三维面形。与现有测量方法相比较,逆向哈特曼阵列拼接测量方法能够在实现纳弧度斜率测量精度的同时,大幅提高测量分辨率和测量口径范围,显著提高测量效率。
Small-scale cluster damage mitigation and detection on fused silica surface (invited)
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摘要: 针对现有小尺寸集群损伤修复及检测技术仍不完善的问题,重点研究亚表面缺陷多模态原位检测方法,从损伤样件表面损伤数量和尺寸、典型小尺寸损伤的形貌、光热吸收、荧光面积等多项指标进行了系统测量和分析,并开展了磁流变修复研究。研究结果表明:熔石英小尺寸损伤内部的吸收性杂质是影响元件性能的主要因素,在磁流变缎带接触到损伤底部前,损伤的整体吸收和荧光分布呈上升趋势;高重频激光对磁流变修复后的损伤辐照过程是一个由慢变快、由杂质到本体、由边缘逐渐向外扩张的过程,能够有效对磁流变修复后的表面进一步起到修复作用,可作为组合修复工艺的第三道工序。研究结果对光学元件检测表征体系的构建提供参考。Abstract: Aiming at the problem that the existing small-scale cluster damage mitigation and detection technology is still imperfect, it focuses on the multi-modal in-situ detection method of sub surface defects, and systematically measures and analyzes the number and size of surface damage of damaged samples, the morphology of typical small-scale damage, light and heat absorption, fluorescent area and other indicators, and carries out magnetorheological repair research. The results show that the absorbent impurities inside the small-scale damage of fused silica are the main factors affecting the performance of the components. Before the magnetorheological ribbon contacts the bottom of the damage, the overall absorption and fluorescence distribution of the damage show an upward trend. The damage irradiation process of high repetition rate laser after magnetorheological repair is a process from slow to fast, from impurity to body, and gradually expanding outward from the edge. It can effectively repair the surface after magnetorheological repair, and can be used as the third process of combined repair process. The research results provide a reference for the construction of optical element detection and characterization system.
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Key words:
- optical engineering /
- fused silica /
- cluster damage /
- damage mitigation /
- multi-modal detection
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表 1 磁流变工艺参数
Table 1. Magnetorheological process parameters
Parameter Rotation number/r·min−1 Rate of flow/L·min−1 Field current/
AIndentation depth/mm Value 260 120 8 0.2 -
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