22 July 2014 Fast optical re-phasing of segmented primary mirrors
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For highly segmented primary mirrors, as that of the European Extremely Large Telescope (E-ELT) with its 798 segments, the capability to update regularly the optical phasing solution is essential for robust operations. The duration of standard phasing procedures is driven by the difficulty of maintaining the registration of the image of the primary on the phasing sensor with tolerances of ~0.02% of the mirror diameter. The paper describes a re-phasing procedure with a dynamic range of about ±1.5 microns. This is based on a standard Shack-Hartmann phasing sensor operated at 2 narrow bands filters with wavelength separation of 30%. Controlled registration offsets are applied during the acquisitions, allowing the registration parameters to be estimated from the phasing data. The procedure has been successfully validated at the Gran Telescopio de Canarias (GTC).
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Henri Bonnet, Henri Bonnet, Michael Esselborn, Michael Esselborn, Nick Kornweibel, Nick Kornweibel, Philippe Dierickx, Philippe Dierickx, } "Fast optical re-phasing of segmented primary mirrors", Proc. SPIE 9145, Ground-based and Airborne Telescopes V, 91451U (22 July 2014); doi: 10.1117/12.2057457; https://doi.org/10.1117/12.2057457

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