Cophasing techniques for extremely large telescopes

Nicholas Devaney; Achim Schumacher

doi:10.1117/12.566310

7 July 2004 Cophasing techniques for extremely large telescopes

Nicholas Devaney, Achim Schumacher

Proceedings Volume 5382, Second Backaskog Workshop on Extremely Large Telescopes; (2004) https://doi.org/10.1117/12.566310
Event: Second Backaskog Workshop on Extremely Large Telescopes, 2003, Backaskog, Sweden

Abstract

The current designs of the majority of ELTs envisage that at least the primary mirror will be segmented. Phasing of the segments is therefore a major concern, and a lot of work is underway to determine the most suitable techniques. The techniques which have been developed are either wave optics generalizations of classical geometric optics tests (e.g. Shack-Hartmann and curvature sensing) or direct interferometric measurements. We present a review of the main techniques proposed for phasing and outline their relative merits. We consider problems which are specific to ELTs, e.g. vignetting of large parts of the primary mirror by the secondary mirror spiders, and the need to disentangle phase errors arising in different segmented mirrors. We present improvements in the Shack-Hartmann and curvature sensing techniques which allow greater precision and range. Finally, we describe a piston plate which simulates segment phasing errors and show the results of laboratory experiments carried out to verify the precision of the Shack-Hartmann technique.

Citation Download Citation

Nicholas Devaney and Achim Schumacher "Cophasing techniques for extremely large telescopes", Proc. SPIE 5382, Second Backaskog Workshop on Extremely Large Telescopes, (7 July 2004); https://doi.org/10.1117/12.566310

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