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Proceedings Paper

On-sky demonstration of the GMT dispersed fringe phasing sensor prototype on the Magellan Telescope
Author(s): Derek Kopon; Brian McLeod; Marcos A. van Dam; Antonin Bouchez; Ken McCracken; Daniel Catropa; William Podgorski; Stuart McMuldroch; Alan Conder; Laird Close; Jared Males; Katie Morzinski; Timothy Norton
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Paper Abstract

The GMT is an aplanatic Gregorian telescope consisting of 7 primary and secondary mirror segments that must be phased to within a fraction of an imaging wavelength to allow the 25.4 meter telescope to reach its diffraction limit. When operating in Laser Tomographic Adaptive Optics (LTAO) mode, on-axis guide stars will not be available for segment phasing. In this mode, the GMT’s Acquisition, Guiding, and Wavefront Sensing system (AGWS) will deploy four pickoff probes to acquire natural guide stars in a 6-10 arcmin annular FOV for guiding, active optics, and segment phasing. The phasing sensor will be able to measure piston phase differences between the seven primary/secondary pairs of up to 50 microns with an accuracy of 50 nm using a J-band dispersed fringe sensor. To test the dispersed fringe sensor design and validate the performance models, SAO has built and commissioned a prototype phasing sensor on the Magellan Clay 6.5 meter telescope. This prototype uses an aperture mask to overlay 6 GMT-sized segment gap patterns on the Magellan 6.5 meter primary mirror reimaged pupil. The six diffraction patterns created by these subaperture pairs are then imaged with a lenslet array and dispersed with a grism. An on-board phase shifter has the ability to simulate an arbitrary phase shift within subaperture pairs. The prototype operates both on-axis and 6 arcmin off-axis either with AO correction from the Magellan adaptive secondary MagAO system on or off in order to replicate as closely as possible the conditions expected at the GMT.

Paper Details

Date Published: 2 September 2016
PDF: 11 pages
Proc. SPIE 9909, Adaptive Optics Systems V, 990946 (2 September 2016); doi: 10.1117/12.2232942
Show Author Affiliations
Derek Kopon, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Brian McLeod, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Marcos A. van Dam, Flat Wavefronts (New Zealand)
Antonin Bouchez, GMTO Corp. (United States)
Ken McCracken, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Daniel Catropa, Harvard-Smithsonian Ctr. for Astrophysics (United States)
William Podgorski, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Stuart McMuldroch, Harvard-Smithsonian Ctr. for Astrophysics (United States)
Alan Conder, GMTO Corp. (United States)
Laird Close, Univ. of Arizona (United States)
Jared Males, Univ. of Arizona (United States)
Katie Morzinski, Univ. of Arizona (United States)
Timothy Norton, Harvard-Smithsonian Ctr. for Astrophysics (United States)

Published in SPIE Proceedings Vol. 9909:
Adaptive Optics Systems V
Enrico Marchetti; Laird M. Close; Jean-Pierre Véran, Editor(s)

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