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13 May 2013 Design and experiment of testing an off-axis aspheric surface by computer generated hologram
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To test an off-axis aspheric surface in high precision, a multiple combined computer generated hologram (CGH) is designed and fabrication. Multiple combined CGH which is a hologram including different areas with different purposes can not only measure off-axis aspheric surface, but also align every element in test system. The design methods of test CGH and alignment CGH were deduced in detail. Ray trace and B-spline were used to devise test CGH, reflection CGH was used to align interferometer and CGH, and hologram alignment mark was used to align CGH and off-axis aspheric surface. A design example was given to test an off-axis paraboloid with 50mm aperture and 35mm off-axis distance. Meanwhile, this CGH was fabricated and this paraboloid was measured by it. The test result (PV=0.305λ,RMS=0.042λ) is matched well with the outcome verified by autocollimation (PV=0.320λ,RMS=0.043λ). At last, we analyzed and solved the noise in the CGH test result. It proves that these designs are correct and this method can test off-axis aspheric surface in high precision.
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Shijie Li, Fan Wu, Qiang Chen, Bin Fan, and Lianghong Li "Design and experiment of testing an off-axis aspheric surface by computer generated hologram", Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 878833 (13 May 2013);

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