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Proceedings Paper

Cophasing techniques for extremely large telescopes
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Paper 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.

Paper Details

Date Published: 7 July 2004
PDF: 9 pages
Proc. SPIE 5382, Second Backaskog Workshop on Extremely Large Telescopes, (7 July 2004); doi: 10.1117/12.566310
Show Author Affiliations
Nicholas Devaney, Instituto de Astrofisica de Canarias (Spain)
Achim Schumacher, Instituto de Astrofisica de Canarias (Spain)

Published in SPIE Proceedings Vol. 5382:
Second Backaskog Workshop on Extremely Large Telescopes
Arne L. Ardeberg; Torben Andersen, Editor(s)

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