Laboratory characterization and performance of the high-order adaptive optics system for the Large Binocular Telescope

We present the laboratory characterization and performance evaluation of the First Light Adaptive Optics (FLAO), the natural guide star adaptive optics system for the Large Binocular Telescope (LBT). The system uses an adaptive secondary mirror with 672 actuators and a pyramid wavefront sensor with adjustable sampling of the telescope pupil from 30 x 30 down to 7 x 7 subapertures. The system was fully assembled in the Arcetri Observatory laboratories and passed its acceptance test in December 2009. The performance measured at different star magnitudes during the acceptance test is shown to lie between the baseline and the goal specifications. In particular, FLAO obtained a 77% Strehl ratio (SR) in the bright end (8.5 magnitude star in the R band) using an H-band filter and correcting 495 modes with 30 x 30 subaperture sampling. In the faint end (16.4 magnitude), a 5% SR correcting 36 modes with 7 x 7 subapertures was measured. The seeing conditions for these tests were 0.8 arcsec (r(0) = 0.14 m at 550 nm) and an average wind speed of 15 m/s. The results for other seeing conditions up to 1.5 arcsec are also presented. The system has been shipped to the LBT site in Arizona, and its commissioning started in March 2010. (C) 2010 Optical Society of America