Error Analysis And Precision Calibration For Interferometric Test Of Aspheric Mirror With Large Aperture Of Space Telescope

With the development of optical manufacturing, optical testing, computer, digital image processing, the space optical system is used in astronomical observation and earth observation. The most used system is Off-axis Three-Mirror Anastigmat(TMA). The TMA optical system not only provides large field, but also provides a flat focal plane and high accuracy of image. The use of aspheric mirror can increase the variable to optimize the quality of system with non-increase the variable of aberration. With the development of space optical technology, the aperture of the optical system is growing, causing the aperture of the optical mirrors becoming larger and larger. It brings challenge to optical manufacturing and testing.Optical testing is the premise of optical manufacturing. The usually testing of aspheric mirror is the testing of outline and interferometer testing. The mirror is polishing needs high precision of testing and usually is tested by interferometer. The interferometer testing includes null testing and non-null testing. Non- null testing includes long wavelength interferometer testing, subaperture stitching and so on. The advantage of non-null testing is the wide scope of application. But the precision of non-null testing is not high enough to test mirror when it is polishing. It usually needs auxiliary optical components such as compensator, CGH for traditional methods when testing large flat mirror, large convex sphere and asphere mirrors. But the precision of null testing is unknown. It is important to calibrate the null testing.In this paper, we mainly studied the calibration of null testing of large aperture mirror and verified the accuracy of the testing based on project examples. The contents of the paper include the following four parts:1, Combined with maximum likelihood estimation and orthogonal fitting of Zernike polynomial theory, we established an algorithm model testing optical plane mirror considering that the error of the reference mirror can’t be ignored. With the algorithm, both the shapes of the reference mirror and the test mirror can be calculated. Simulation is performed combined to verify the accuracy and reliability of the algorithm.2, Errors of CGH induced by designing, manufacturing and encoding were studied. Manufacturing errors of CGH are the main errors. The manufacturing errors of CGH include substrate errors, pattern distortion, duty-cycle errors, etching phase errors and amplitude errors. At the meantime, a particular CGH is designed to calibrate errors of CGH. The calibration guides the design of CGH to test aspheric mirror with high precision. The effectiveness of the model was also verified with engineering examples.3, We studied the theory of null corrector testing to asphere mirrors, designed a null corrector to test an aspheric mirror. Combined the theory of CGH, a tilted CGH is designed to test null corrector. Errors of null corrector and CGH can be separated by ML algorithm. Influencing factors of null corrector were analyzed to get the way to increase the precision of null lens and the testing accuracy of the model was calculated with engineering examples.4, We designed a CGH and null corrector to test an aspheric mirror which is polishing, analyzed the precision of CGH and null corrector and got the precision of testing of aspheric mirror by CGH and precision of testing of aspheric mirror by null corrector. At the same time, we contrasted the testing result of aspheric mirror by null corrector and CGH and verified the process of calibration.