Adaptive optics for the Euro50: design and performance

The optical design for the proposed Euro50 extremely large telescopewith integrated adaptive optics (AO) is presented. For atmosphericturbulence correction, we propose using single and dual-conjugate AOsystems working with natural and laser guide stars. The corrective shapeof the deformable mirrors (DMs) is derived from an analytical algorithmbased on minimization of the sum of the residual power spectra of thephase fluctuations seen by guide stars after correction. Predictions forperformance of the Euro50 ELT with Dual-conjugate AO are given for the Kband using a seven layer atmospheric model for the atmosphere at theObservatorio del Roque de los Muchachos (ORM) on La Palma. The averageStrehl ratio is used to quantify the system performance for differentvalues of actuator pitch and DM conjugation altitudes. The influence ofthe outer scale and telescope pointing on the RMS stroke of the DMs ispresented. It is concluded that construction of such a system isfeasible and that there is a need for development of a simulation toolto verify the analytical calculations. Precise knowledge of the outerscale of the atmosphere at the ORM is needed to establish the dynamicalrange of the mirrors.