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Proceedings Paper

MMT adaptive secondary: first AO closed-loop results
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Paper Abstract

The adaptive secondary for the MMT is the first mirror of its kind. It was designed to allow the application of wavefront corrections (including tip-tilt) directly at the secondary mirror location. Among the advantages of such a choice for adaptive optics operation are higher throughput, lower emissivity, and simpler optical setup. Furthermore, this specific implementation provides capabilities that are not found in most correctors including internal position feedback, large stroke (to allow chopping) and provision for absolute position calibration. The mirror has now been used at the MMT during several runs where it has performed reliably. In this paper we discuss the mirror operation and AO performance achieved during these runs in which the adaptive secondary has been operating in conjunction with a Shack-Hartmann wavefront sensor as part of the MMT adaptive optics system. In particular we mention a residual mirror position error due to wind buffeting and other errors of ≈ 15 nm rms surface and a stable closed loop operation with a 0dB point of the error transfer function in the range 20-30 Hz limited mainly by the wavefront sensor maximum frame rate. Because of the location of the adaptive secondary with respect to the wavefront sensor camera, reimaging optics are required in order to perform the optical interaction matrix measurements needed to run the AO loop. This optical setup has been used in the lab but not replicated at the telescope so far. We will discuss the effects of the lack of such an internal calibration on the AO loop performances and a possible alternative to the lab calibration technique that uses directly light from sky objects.

Paper Details

Date Published: 24 December 2003
PDF: 11 pages
Proc. SPIE 5169, Astronomical Adaptive Optics Systems and Applications, (24 December 2003); doi: 10.1117/12.508411
Show Author Affiliations
Guido Brusa, Steward Observatory/Univ. of Arizona (United States)
Osservatorio Astrofisico di Arcetri (Italy)
Armando Riccardi, Osservatorio Astrofisico di Arcetri/INAF (Italy)
Francois P. Wildi, Steward Observatory/Univ. of Arizona (United States)
Michael Lloyd-Hart, Steward Observatory/Univ. of Arizona (United States)
Hubert M. Martin, Steward Observatory/Univ. of Arizona (United States)
Richard Allen, Steward Observatory/Univ. of Arizona (United States)
Donald L. Fisher, Steward Observatory/Univ. of Arizona (United States)
Douglas L. Miller, Steward Observatory/Univ. of Arizona (United States)
Roberto Biasi, MicroGate Srl (Italy)
Daniele Gallieni, ADS International Srl (Italy)
Fabio Zocchi, Media Lario Srl (Italy)

Published in SPIE Proceedings Vol. 5169:
Astronomical Adaptive Optics Systems and Applications
Robert K. Tyson; Michael Lloyd-Hart, Editor(s)

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