Characteristics and performances of the small and large field adaptive optics system AOC at the C2PU telescope

Description

AOC (Adaptive Optics system at Calern) is an adaptive optics bench being developed on the Epsilon (East) telescope of the two 1-m telescopes of C2PU (Centre Pédagogique Planète Univers), Calern observatory, Observatoire de la Côte d'Azur (OCA), near Nice (France). It is installed at the F/35 Coudé focus, and aims at correcting the wavefront in the visible and in the near-infrared, using an ALPAO 11x11 actuator-across deformable mirror feeding a 10x10 Shack-Hartmann wavefront sensor. It is currently being upgraded with a First Light Imaging OCAM2 EMCCD detector, which will allow us to increase the number of available pixels per sub-aperture and the loop frequency, as well as to take advantage from a negligible read-out.

The system is designed to work both in a standard stellar mode and in a more innovative planetary mode, capable of operating on planets such as Mars, Saturn and Jupiter, with a field up to 60 arcsec. Such a wide field is much larger than the isoplanatic angle, therefore only the turbulent ground layer can be corrected, up to an altitude of a few thousand meters. Extensive simulations have been carried out of these two different modes. The system is now undergoing implementation and validation using a low order modal control (10 to 16 modes), but a zonal control will be implemented next to ensure performance improvement down to λ ∼ 500 nm. The loop frequency was limited to 500 Hz by the speed of the Andor iXon camera, but its replacement by an OCAM2 camera will allow to reach between 1.5 and 2.2 kHz (depending on binning). Theoretical performance of the system has been studied through simulations for the planetary mode and presented previously at SPIE. 1 Here we present the implementation of the system and its preliminary performance on the sky and comparison with the simulations.

In the future, we plan to better characterize the temporal transfer function as a function of the gain and the number of corrected modes, in order to implement an automatic gain control, both zonally in the visible and modally for near infrared applications. We are also implementing a control of the non-common path aberrations (NCPA). This is done by analysing the aberrations on a defocused stellar image, using the DONUT algorithm. 2 We intend to characterize these NCPA in real-time directly from the observations. We also consider parameterizing the resulting point-spread function from the real-time statistics of the adaptive optics system to be used for further data analysis

Abstract

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