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14 September 2011 In-process testing for cryo-figuring 1.5 meter diameter auto-collimating flats
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Three auto-collimating flats (ACFs) of 1.5 meter clear aperture are being manufactured for use in the JSC Cryo-Optical Metrology test of the James Webb Space Telescope. In-process interferometric testing of the ACFs is used to guide their surface-figure processing. The surface measurement is performed in a vacuum chamber at both room (+20 °C) and cryogenic (-240 °C) temperatures. With a 12-inch beam diameter FizCam interferometer, sub-aperture measurements are taken across the ACF diameter at multiple rotations. These measurements are stitched together to compute the surface figure. The figure change between room-temperature and cryogenic temperature is measured and used to enable cryo-figuring based on room-temperature measurements. The data analysis is calibrated to account for gravity sag on test-set optics and surface aberrations caused by vacuum pressure and temperature gradients on vacuum-chamber windows. The first ACF is complete and meets specification with surface error of less than 75 nm RMS.
© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
David J. Fischer, Joseph Hayden, James K. Lawton, Brandon Olson, Chris Brophy, and Scott Kennard "In-process testing for cryo-figuring 1.5 meter diameter auto-collimating flats", Proc. SPIE 8146, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts V, 81460A (14 September 2011);

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