Control strategy for the adaptive optics of the Euro50

Abstract:
The scheme presently envisaged for the EURO50 adaptive optics ispresented. The Euro50 adaptive optics will primarily work with laserguide 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 SCAOoperation using a single NGS is evaluated. An algorithm for optimalcontrol of the deformable mirrors (DMs) using LGSs and Shack-Hartmanwavefront sensors is presented and commented upon. It is an extension ofa recently developed algorithm for optimal control using NGSs andworking in the spatial Fourier domain. In addition the concept of avirtual wavefront sensor is introduced to overcome the difficulty intransmitting a large number (37) of LGSs to the final DCAO focus withboth adequate field and adequate aberrations. The expected performanceis estimated in form of maps of the Strehl ratio versus field angleusing a standard seven layer atmospheric model for the Observatorio delRoque de los Muchachos (ORM) site on la Palma for the case of the outerscale being either 20 m (nominal for ORM) or infinity (Kolmogorov - mostpessimistic case).