| 题名 | 光学元件亚表面缺陷的无损检测研究 |
| 作者 | 崔辉 |
| 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 | 赵元安 |
| 关键词 | 亚表面缺陷 全内反射显微法 散射 显微镜 微调焦 |
| 其他题名 | Study on nondistructive detection methods for subsurface damage in optics |
| 中文摘要 | 随着强激光系统中激光通量的逐渐提高，强激光辐照造成的元件损伤直接影响了元件的寿命和强激光系统的运作。提高光学元件的抗激光损伤能力是光学元件制备和使用过程中最关键和最重要的挑战。研究发现，位于表面以下的亚表面缺陷是制约元件激光损伤阈值提高的重要因素。对亚表面缺陷进行无损的检测评估是研究亚表面缺陷产生机理的基础，而当前亚表面缺陷的无损检测技术并不成熟。本文以全内反射显微法为切入点对亚表面缺陷的检测进行了初步探讨，主要内容包括以下几个方面： 分析了全内反射显微法的原理，讨论了不同种类缺陷的散射类型：杂质颗粒等小型缺陷的散射属于Mie散射，颗粒尺寸越大，散射场能量分布的方向性越明显；以划痕为代表的大尺寸缺陷的散射属于衍射散射，由夫琅和费衍射可以计算出其散射光的远场分布。讨论了照明光的通量密度、缺陷大小、以及显微镜对缺陷散射光的接收角对缺陷散射光斑的影响。 搭建了全内反射显微平台，实现了平台操作的自动化。使用该平台对亚表面缺陷进行了观测研究，验证了驻波场对缺陷可见度的影响。实验中发现，当划痕与入射面的夹角达到一个阈值位置θvanish，划痕将从视场中消失，且θvanish与显微镜的数值孔径角相等。本文从衍射散射的角度分析划痕的散射，认为全内反射显微成像的过程中，划痕显现的方向性是光源照明的不均匀造成的。在考虑到这种方向性后，本文获得了包含各个方向划痕信息的TIRM（Total Internal Reflection Microscope, TIRM）图像。 提出一种结合全内反射显微技术和数字图像处理技术获得光学元件亚表面缺陷分布信息的新方法。利用显微镜系统的有限景深对亚表面缺陷沿深度方向分别进行散射成像，可以获得不同离焦量下的散射图像，通过数字图像处理技术，建立散射图像清晰度评价函数与离焦量的关系，通过清晰度曲线得到亚表面缺陷的深度位置及深度尺寸。本文模拟全内反射显微图像的获得过程，讨论微调焦过程中全内反射显微成像的特点。缺陷深度位置及纵向尺寸的测量精度主要由载物台精密调焦机构的精度以及显微镜的景深决定，一般可达微米量级。本文利用飞秒激光加工技术制备尺寸和位置已知的微结构，使用微调焦法准确获得了微结构信息，验证了该方法的有效性。 讨论了TIRM平台的扩展应用，探讨了TIRM质量与加工工艺的关系。第一次将全内反射显微法用于经过CO2激光修复后的样品观测。实践表明，全内反射显微法可以很好地对CO2激光修复的结果作出评估。 |
| 英文摘要 | With the power of laser increasing rapidly, laser induced damage threshold(LIDT) of optics is urgent supposed to be improved. Studies have shown that subsurface damage (SSD) detection and removal play an important role on improving the LIDT of optics. Currently nondestructive testing technologies for SSD are not mature. In this paper, we choose total internal reflection microscopy(TIRM) as the cut-in point and discuss the nondestructive testing technologies for SSD. We have carried out the fundamental research in the following respects: The principle of total internal reflection microscopy is analyzed. The scattering type of SSD can be divided into two categories: the scattering of impurity particles belongs to Mie scattering. The larger the particle is, the more uneven the distribution of energy scattered field will be. The scattering of scratches is diffraction and the far-field distribution of scattered light of scratches can be calculated by using the fraunhofer diffraction formula. In this paper, we also discuss the factors that affect scattering spots in TIRM images. We build a TIRM and realized the automation of the platform. Using the TIRM, we study the influence of the standing wave field distribution on the defect visibility. In our experiments we find that there is a strong dependence of scratch visibility on the angle(θ) between the scratch and normal direction of the incident plane. In this paper, the scattered field distribution of a scratch and the imaging properties of a microscope are analyzed. Simulation results show that the scattered energy distribution of a scratch is perpendicular to the scratch. The propagation direction of primary scattered energy depends upon the incident angle and the angle θ. While the energy received by the microscope is high order diffraction components of the scattered light in TIR-illumination mode. With the increase of θ, the scattered energy will gradually deviate from the center and finally be out of the field of view. We believe that it is the anisotropy of illumination in TIR-illumination mode that causes the visibility changes of a scratch. After taking this directionality into consideration, we propose an experimental method for TIRM to take picutures with all scratches in all directions in one image. We propose a new method to detect the distribution of SSD. This method combines total internal reflection microscope and digital image processing technology. Because of the limited focal depth of the microscope system, one can get different TIRM images focusing at different depth levels. We establish the connection between the definition curve of TIRM image sequence and the depth position of SSD. We can also obtain the depth length of SSD through the feature of definition curve. We simulate the imaging process of TIRM and find out the typical features of the focusing process. We fabricated microstructures by femtosecond laser micromachining and got the size information of the microstructures exactly. Focal depth of the microscope determines the test depth accuracy of our method and actually the test accuracy can achieve 1μm. Finally, we discuss the extended applications for TIRM. We explore the relationship bettween TIRM quality and different fabrication technologies for optics. Moreover, we apply TIRM to evaluate the effect of CO2 laser treatment for mitigation suface damage grouth for the first time. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/16853]  |
| 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 | 崔辉. 光学元件亚表面缺陷的无损检测研究[D]. 中国科学院上海光学精密机械研究所. 2014. |
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