数字全息术用于光学元件表面缺陷形貌测量

利用像面数字全息显微术对光学元件表面缺陷的三维形貌测量进行了理论及实验研究。设计并搭建了相应光路系统记录全息图,采用角谱算法数值重建物光场,通过相位修正消除了系统误差引入的波前畸变,获得了经过待测光学元件表面缺陷调制的物光相位分布,并根据建立的相位分布与表面缺陷面形的关系模型计算得到缺陷三维形貌。实验以多个划痕和麻点等常见表面缺陷作为测量对象,分别获得了它们的三维形貌,以其中一条实际宽度为35μm、深度为270nm的划痕为例,测量得到该划痕的宽度为35.21μm,平均深度为267.6nm,与真实值相比,横向测量误差为0.6%,纵向测量误差为0.9%。实验结果证实该测量方法是有效、可靠的,能够准确测量光学元件表面缺陷的三维形貌,因而有助于判断光学元件损伤程度以及分析缺陷对系统波前的影响,对保障高功率激光装置的安全正常运行有重要意义。

Measurement of surface defects of optical elements using digital holography

In order to measure the three-dimensional microstructure of surface defects on optical components,a novel measuring system based on digital image-plane holographic microscopy (DIPHM) was proposed and experimentally designed.The optical path of the system was built to record digital holograms,which comprised phase information of object light.The object light wavefront was reconstructed by the angular spectrum algorithm,and the wavefront distortion attributed to the system errors was eliminated via phase correction.Therefore the phase distribution of the object light modulated by the surface defects was obtained.By deducing the relationship between the object light wavefront and the surface topography,the 3D microstructure of the surface defects was determined.Furthermore,some optics with scratches and pits were measured as samples.For one scratch with width of 35.00 μm and depth of 270.0 nm,the measuring results were as follows:the width is 35.21 μm and the depth of 267.6 nm,thereby the transverse and vertical errors are 0.6％ and 0.9％ respectively.The results indicate that this measuring method can determine the 3D microstructure of surface defects on optics feasibly and accurately.In addition,it is helpful to judge the damage degree of the optical component and analysis the influence of surface defects,thus of great significance to ensure the laser system security running.