Study On Testing Of Large Flat Mirrors

With the development of science and technology, the large aperture optical systems are used widely more and more in all kinds of fields. The large flat mirror is used as the reference mirror for the testing of optical systems. As the rail of high accuracy, the large flat mirrors play an important role in the"large-scale high-precision ruling system of diffraction grating".Ritchey-Common test is a traditional method for testing of large flat mirrors. Only qualitative test can be done with the help of knife-edge apparatus. With the invention of laser digital interferometers, it is possible to process the data that are collected in use of digital interferometers. The influence caused by the small displacement of incident angle on the large flat mirror is analyzed. In the same time, errors introduced by the measured errors of Ritchey angle are analyzed. When the measured errors of Ritchey angle is smaller than 0.4°,the results of testing have an high accuracy. To remove the errors introduced by alignment of system, the relationships between the flat coordinate system and the pupil coordinate system in Ritchey-Common test are derived, based on which, the algorithms used in the two angular positions of Ritchey-Common test are composed. The algorithms are verified by the simulations, which show that residual errors in the form of PV are 10-7 order of magnitude.A method used for the test of large rectangular flat with high aspect in use of Skip-Flat test is introduced. The large rectangular flat is tested in full aperture in use of small aperture interferometer. The collected map is compressed in the direction of optical axis in Skip-Flat test, to guide optical manufacturing, the map is expand and interpolated.However, the research on testing of large flat mirrors remains to be further. The algorithms of two angular positions in Ritchey-Common test remain to be verified in experiments. The study on the combination of Ritchey-Common test with subaperture stitching method is expected for testing of larger flat mirrors.