一种基于临界角法检焦系统的设计

临界角法检焦是利用光波在临界角附近的反射特性来检测聚焦状态，它具有分辨力高、损失光能小、结构简单、系统调试容易的特点，是亚微米级离焦检测的首选方法之一。根据菲涅尔公式，并通过合理假设，利用高斯光学公式可以得到离焦误差信号的计算公式。实验采用单光路临界角法，利用He-Ne激光器、临界角棱镜、四象限光电探测器、信号采样电路、数据采集卡等元器件组成了离焦检测系统，实现了离焦信号的提取；通过数字滤波、归一化处理等技术得到离焦误差信号（FES），以此获得了FES的大小和变化趋势与离焦量的关系曲线，为临界角法离焦检测系统的工程实现提供了参考。

Design on Focus Error Detect System with Critical-Angle Method

Critical-angle method with the theory of reflect character of light wave by critical angle, is a preferred method of sub-micrometer grade because of its advantages, such as high resolution, low light-energy loss, simple framework and easy to calibrate. The expression of defocus is deduced with Gauss optical formula based on Fresnel formula and legal hypothesis. The error of defocus is gained with single light path critical-angle method. The detecting system consists of He-Ne laser, critical angle prism, four-element photodetector, signal sampling circuit and data acquisition card, etc. The curve of value and direction of focus error signal (FES) is extracted with digital filter and normalization technology. It offers the reference of engineering application of focus defect system with critical-angle method.