An optimized controller for ARGOS: using multiple wavefront sensor signals for homogeneous correction over the field

ARGOS is the ground layer adaptive optics system planned for the LBT. The goal of such a ground layer adaptive optics system is to provide a maximum homogeneity of the point spread function over the full field of view. Controllers for optimized correction with an adaptive optics system with guide star and science target at different field angles are well known in the case of a single guide star. As ARGOS uses three laser guide stars and one auxiliary natural guide star a weighting scheme is required to optimize the homogeneity using all available information. Especially the tip and tilt modes measured by the one single off axis guide star and estimated thereof over the field will need to be improved by incorporation of the laser measurements. I will present the full scheme for an optimized controller for the ARGOS system. This controller uses the wavefront signals of the three lasers to additionally reconstruct the lower atmosphere. Information on the higher atmosphere will be provided by a DIMM-MASS instrument. The control scheme is tested analytically and the variation of the point spread function is then measured over the full field.