Reconstruction of the point spread function for the ground layer adaptive optics system ARGOS

Present and future adaptive optics (AO) systems aim for the correction of the atmospheric turbulence over a large field of view combined with large sky coverage. Thus they use multiple laser beacons on sky. Still there will always be variations in the shape of the point spread function (PSF) with field angle. To overcome this drawback, a good knowledge of the PSF over the field is required. In the past, several algorithms of PSF retrieval have been proposed and tested. This includes on-axis PSF retrieval from wavefront sensor (WFS) data as well as a correction over the field using a reference PSF. The schemes have been set up for both an AO system using a single natural guide star as well as a system using a laser beacon. For these algorithms to work, a detailed knowledge of the atmospheric structure, i.e. Cn2 profile, is crucial. In the context of the ARGOS system, a GLAO system proposed for the LBT with three Rayleigh laser beacons per eye of the telescope, we build a reconstruction scheme which uses the multiple guide stars to directly measure the atmospheric profile from the WFS data itself. Here we show how the conventional PSF-retrieval algorithms must be changed to make up for the difference between the multiple beacon GLAO used in ARGOS and the typical single source on-axis schemes. We present first results of PSF-reconstruction using the data from two WFS and investigate in the accuracy of this procedure