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30 January 2003 Mach Zender wavefront sensor for phasing of segmented telescopes
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Segmented mirror technology has been successfully applied to 10m class telescopes (Keck, HET, GTC) and is widely recognized as mandatory for Extremely Large Telescopes. For optimal performance the wavefront error associated with segmentation should remain within conservative limits, typically 1/20th of a wave. Several phasing techniques and associated metrologies are under development, with a view to extrapolate such methods to the 100-m OWL telescope. We investigate a novel technique based on Mach-Zehnder interferometry, whereby the wavefront in one of the interferometer arms is spatially filtered so as to provide a reference wave, prior to having the two arms recombined to produce suitable interferograms. We introduce a theoretical description of the interferometer, as well as results of simulations, showing that with proper settings of the interferometer's parameters, the technique can be made insensitive to atmospheric turbulence and, more generally, to almost any error source not associated with the segmentation. It also appears that, in a telescope that would include more than one segmented mirror, simple processing allows to disentangle the signal associated to each of them. Finally, we outline the development still required to complete a full qualification of this approach.
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Luzma Montoya Martinez, Natalia Yaitskova, Philippe Dierickx, and Kjetil Dohlen "Mach Zender wavefront sensor for phasing of segmented telescopes", Proc. SPIE 4840, Future Giant Telescopes, (30 January 2003);

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