AOLI: Wavefront curvature sensor algorithms and their performance at low photon numbers
Jonathan Crass (1), Bruno Femenía (2,3), David King (1), Craig Mackay (1), Rafael Rebolo (2,4), Lucas Labadie (5), Antonio Pérez Garrido (6), Marc Balcells (2,7), Anastasio Díaz-Sánchez (6), Jesús J. Fuensalida (2,3), Roberto López (2), Alex Oscoz (2), Jorge A. Pérez Prieto (2,3), Luis F. Rodríguez (2), Isidro Villó (6)
(1) Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK (2) Instituto de Astrofísica de Canarias, C/ Vía Láctea S/N, E-38200 La Laguna, Spain (3) Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain (4) Consejo Superior de Investigaciones Científicas, Spain (5) I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50397 Köln, Germany (6) Universidad Politécnica de Cartagena, Campus Muralla del Mar, Cartagena, Murcia E-30202, Spain (7) Isaac Newton Group of Telescopes, Apartado de Correos 321, E-38700 Santa Cruz de la Palma, Canary Islands, Spain
The combined techniques of Lucky Imaging and low-order Adaptive Optics (AO) have already delivered diffraction limited images in the visible (35 milliarcsecond resolution in the I band on a 5 metre ground-based telescope). The need to be able to work at this resolution for a wide range of astronomical problems requires significant sky coverage using natural guide stars fainter than 18th magnitude. The Adaptive Optics Lucky Imager (AOLI) combines Lucky Imaging and low-order AO to provide diffraction limited imaging using a single instrument.
AOLI comprises a camera similar to the ’LuckyCam’ developed at the Institute of Astronomy, University of Cambridge. The camera uses a 2x2 array of 1k square electon multiplying CCDs providing a corrected field of view of 30-120 arcseconds in diameter. The low-order Adaptive Optics component of AOLI employs a quad plane wavefront curvature sensor to determine wavefront distortions (Guyon, 2010) combined with a deformable mirror to apply corrections. This method allows faint natural guide stars to be used which is of key importance for milliarcsecond imaging at visible wavelengths.
Current work focuses primarily on the development of hardware and software algorithms for the AO system. The specifications for the system are presented with a discussion of the wavefront reconstruction algorithms, their performance and the requirement for high performance computing (e.g. GPUs). Characterising the effects of the curvature sensor at very low photon numbers is ongoing with a view to performing experimental comparisons with traditional Shack Hartmann sensors.