11 October 2012 Study on measurement of 160 mm convex hyperbolic mirror for Cassegrain reflecting system
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Abstract
In this study, the measurement of a 160 mm convex hyperbolic mirror by using the 6 inches phase shifting interferometer and the CGH (computer-generated hologram) in a vertical setup is presented. The wavefront errors of the metrology system including the reference flat and CGH flat due to gravity effect are measured and calibrated by using random testing and null cavity testing with and without CGH. Then, the real form error of each single sub-aperture could be acquired by subtracting the system wavefront errors. In this study, we measured form errors of 10 off-axis sub-apertures with equal angle space and then stitched them to establish the whole irregularity in the shape of the mirror in 160 mm diameter. Finally, we imported the irregularity in the shape of the mirror to the CNC aspheric polishing machine for correction polishing. Combining the aspheric metrology technique and the CNC aspheric polishing technique, a 160 mm secondary mirror for the Cassegrain reflecting system was finished within PV 0.15μm and RMS 17.9 nm.
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Cheng-Fang Ho, Cheng-Fang Ho, Zong-Ru Yu, Zong-Ru Yu, Ching-Hsiang Kuo, Ching-Hsiang Kuo, Wei-Yao Hsu, Wei-Yao Hsu, "Study on measurement of 160 mm convex hyperbolic mirror for Cassegrain reflecting system", Proc. SPIE 8486, Current Developments in Lens Design and Optical Engineering XIII, 84860Q (11 October 2012); doi: 10.1117/12.928353; https://doi.org/10.1117/12.928353
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