Control strategy for the adaptive optics of the Euro50

The scheme presently envisaged for the EURO50 adaptive optics is presented. The Euro50 adaptive optics will primarily work with laser guide stars (LGSs) and control of either one or two deformable mirrors (SCAO and DCAO respectively), but operation using a natural guide star (NGS) is also foreseen. The point spread function (PSF) for SCAO operation using a single NGS is evaluated. An algorithm for optimal control of the deformable mirrors (DMs) using LGSs and Shack-Hartman wavefront sensors is presented and commented upon. It is an extension of a recently developed algorithm for optimal control using NGSs and working in the spatial Fourier domain. In addition the concept of a virtual wavefront sensor is introduced to overcome the difficulty in transmitting a large number (37) of LGSs to the final DCAO focus with both adequate field and adequate aberrations. The expected performance is estimated in form of maps of the Strehl ratio versus field angle using a standard seven layer atmospheric model for the Observatorio del Roque de los Muchachos (ORM) site on la Palma for the case of the outer scale being either 20 m (nominal for ORM) or infinity (Kolmogorov - most pessimistic case).