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Closed loop operation with extremely elongated LGS spots in CANARY Phase D
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Paper Abstract

CANARY is a wide-field AO on-sky test facility which has been operated annually on the 4.2m William Herschel Telescope since 2010. CANARY has the stated goal of testing and demonstrating AO technologies that are critical for ELT AO performance. It has seen four distinct phases where new AO technologies have been developed and demonstrated, including NGS MOAO in 2010 (phase A), Rayleigh LGS and NGS MOAO in 2012 and 2013 (phase B, with LGS commissioning in 2011), LTAO operation in 2014 and 2015, and finally operation with a single Sodium laser guide star launched far off axis in 2016 and 2017 (phase D). By launching this laser guide star 40m off axis, extremely elongated laser guide star spots are created in the CANARY LGS Shack-Hartmann wavefront sensor. Therefore, the 7×7 sub-apertures of CANARY can be used to test wavefront sensing performance of a sub-pupil of the ELT located furthest from the laser launch axis. We present an overview of CANARY in its phase D configuration. Depending on where in the sky the LGS is pointing, the projected baseline between the on-axis LGS wavefront sensor and the laser launch location, as seen by the wavefront sensor, will vary from about 20-40m, allowing us to artificially generate different degrees of elongation. Additionally, the well sampled CANARY sub-apertures have 30×30 pixels each and a 20 arcsecond field of view, using an OCAM2S EMCCD camera. This means that by shrinking sub-apertures, and optionally by binning pixels, we are able to investigate different pixel scales and fields of view for the ELT systems, thus determining the optimal design parameters. Here we discuss the closed loop tests that were performed to investigate the effect of spot truncation and extreme elongation. We include different correlation techniques, including standard FFT-based correlation, brute force correlation and correlation by difference squared. We also mention dynamic and automatic updates of the correlation reference images while the AO loop is engaged that have previously been reported. The matched filter algorithm is also mentioned, with a pointer to our prior on-sky investigations. We give our recommendation for the ELT wavefront sensing algorithm of choice, and our evidence based reasons for this recommendation, which may come as a surprise to some. Finally we also present the future experiments to be performed with CANARY, give details of the OPTICON funded programme which enables the hosting of AO experiments on CANARY, allowing the AO community to get involved.

Paper Details

Date Published: 10 July 2018
PDF: 9 pages
Proc. SPIE 10703, Adaptive Optics Systems VI, 1070325 (10 July 2018); doi: 10.1117/12.2313263
Show Author Affiliations
Alastair G. Basden, Durham Univ. (United Kingdom)
Lisa Bardou, Observatoire de Paris (France)
Domenico Bonaccini Calia, European Southern Observatory (Germany)
Jean-Tristan Buey, Observatoire de Paris (France)
Julio Castro, Instituto de Astrofísica de Canarias (Spain)
Mauro Centrone, INAF - Osservatorio Astronomico di Roma (Italy)
Fanny Chemla, Observatoire de Paris (France)
Jean-Luc Gach, Lab. d'Astrophysique de Marseille (France)
Eric Gendron, Observatoire de Paris (France)
Deli Geng, Durham Univ. (United Kingdom)
Zoltan Hubert, Observatoire de Paris (France)
Gianluca Lombardi, Instituto de Astrofísica de Canarias (Spain)
Douglas J. Laidlaw, Durham Univ. (United Kingdom)
Tim J. Morris, Durham Univ. (United Kingdom)
Richard M. Myers, Durham Univ. (United Kingdom)
James Osborn, Durham Univ. (United Kingdom)
Andrew P. Reeves, Durham Univ. (United Kingdom)
Gerard Rousset, Observatoire de Paris (France)
Arnaud Sevin, Observatoire de Paris (France)
Matthew Townson, Durham Univ. (United Kingdom)
Fabrice Vidal, Observatoire de Paris (France)

Published in SPIE Proceedings Vol. 10703:
Adaptive Optics Systems VI
Laird M. Close; Laura Schreiber; Dirk Schmidt, Editor(s)

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