Laurie Pham, Olivier Lardière, Colin Bradley
University of Victoria
Multi-Object Adaptive Optics (MOAO) is an adaptive optics technique in development for Extremely Large Telescopes and will allow simultaneous observation of up to 20 targets in a several arc-minute field-of-view. Raven is an MOAO pathfinder developed by the Adaptive Optics Laboratory of the University of Victoria, in collaboration with the Herzberg Institute of Astrophysics and the Subaru Telescope. Its goal is to demonstrate that MOAO technical challenges such as open-loop control and calibration are achievable on-sky and also to deliver science results. The open-loop (OL) approach makes the need for calibration even more crucial.
We will present the specific calibration procedures of Raven in two steps. The first one is to find the command matrices between the three open-loop wavefront sensors (WFS) with the two deformable mirrors (DM) used to correct the wavefront on the science paths. Because of the OL, we add components such as a calibration-DM in front of the whole system and also close-loop WFS behind each DM. We register the DM with the CL-WFS and then the calibration-DM with all of the five WFS and then compute the command matrices. The goal of the second step is to remove the field-dependent non-common path aberrations (NCPAs). That task is common in AO systems but presents a bigger challenge in this case because of the longer optical paths, the open-loop control and also the moving pick-off arms.