On-sky testing of algorithms for extended LGS spots

Abstract

We present results of on-sky testing of different algorithms for highly extended LGS spots. We have used the CANARY wide-field AO demonstrator instrument on the 4.2m William Herschel Telescope on La Palma with the ESO Wendelstein LGS unit, launched 40m off-axis to simulate edge sub-apertures of the E-ELT. We investigate the performance of correlation and matched filter algorithms, comparing performance with a traditional centre of gravity. We also present on-sky tests of advanced pixel handling algorithms which we show improve AO system performance, including adaptive windowing (spot tracking), total variation minimisation and brightest pixel selection. Techniques to improve detection of truncated spots are also presented. Additionally, we present a critical study of Shack-Hartmann sensor accuracy with accurate detector readout models, highly applicable to AO system designers when specifying detector performance, or for predicting AO system performance with a given detector.