Digital Knife-edge Testing Technology On Spherical Mirror Of Large Aperture

Rapid development of optical processing technique calls for new requirement for surface characterization testing technology on spherical mirror of large aperture. Knife-edges and interferometers are the two common tools: Knife-edges feature simpleness, versatility, high sensitivity and cost performance, especially suit for real-time measurement of large aperture optics. Nevertheless based on the contrast sensitivity of human eye, knife-edges can only perform qualitative instead of quantitative measurement; accordingly it limits advancement of manufacturing technique. Interferometers with high accuracy and sensitivity, low stability and bulk dimensions don't suit for real-time measurement of large aperture optics. For the interferometer, it's hard to produce a standard mirror with large aperture, which always leads to high cost. Therefore, real-time quantitative measurement of large aperture optics is the focus of research nowadays.On the basis of traditional knife-edge, combined with CCD image processing, computer-aided calculating, digital knife-edges formed to rapidly perform quantitative measurement of optics of large aperture, which largely widen application of knife-edge technology. Depending on merits of simple structure, high sensitivity and versatility, digital knife-edges take advantage of knife-edgesand interferometers, and provide guidance for processing of large aperture optics.This paper introduces the status of surface characterization testing and two common means used for optics' surface characterization testing, puts forward the technology of digital knife-edge, and validates the feasibility of digital knife-edge technology.The main work included is just as below:· sets up experimental instrument, and performs research on large aperture optics;· deduces mathematical expression;· calculates darkness threshold via fitting pixel's grayscale;· reconstructs surface characteristics;· evaluates surface characterization with parameters of P-V,RMS,PSD, phase gradient and so on, makes experiment with reflector of large aperture;· programs digital knife-edge measurement software;· analyzes system's aberration;· analyzes system's error.