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11 October 2010 Phase retrieval in situ measurement for large aperture parabolic mirror
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Phase retrieval is a promising method for in-situ metrology and has been applied to spherical mirror surface metrology successfully. To meet the requirement of in-situ measurement in manufacturing large aperture parabolic mirror, a new method using phase retrieval technology is developed. In this method, an approximately parallel beam is used to illuminate the large parabolic mirror. The beam is produced by a point light source far away from the tested mirror. Then, intensity of diffraction patterns near the focus is measured by CCD. The experiment of testing a parabolic mirror with aperture 400mm and radius of curvature at vertex 2789.7mm is described. And some advices of improving the setup are presented. Errors brought by the approximately parallel beam are compensated by an algorithm derived from GS iterative algorithm. Phase retrieval result is consistent with that measured by interferometer sub-aperture stitching in error distribution, PV value and RMS value. The experiment shows that this method features simple optical path, good anti-vibration ability and acceptable accuracy.
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Lingyan Ding, Yulie Wu, Shengyi Li, Yang Liao, and Yong Shu "Phase retrieval in situ measurement for large aperture parabolic mirror", Proc. SPIE 7656, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test and Measurement Technology and Equipment, 765602 (11 October 2010);

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