The E-ELT Multi-Conjugate Adaptive Optics module
E. Diolaiti (1), I. Foppiani (1,2), J.-M. Conan (3), R. C. Butler (4), R. I. Davies (5), A. Baruffolo (6), M. Bellazzini (1), G. Bregoli (1), P. Ciliegi (1), G. Cosentino (2), B. Delabre (7), T. Fusco (3), N. Hubin (7), M. Lombini (1,2), E. Marchetti (7), C. Petit (3), C. Robert (3), L. Schreiber (2)
(1) INAF – Osservatorio Astronomico di Bologna (Italy) (2) Università di Bologna – Dipartimento di Astronomia (Italy) (3) Office National d’Études et Recherches Aérospatiales (France) (4) INAF – Istituto di Astrofisica Spaziale e Fisica cosmica di Bologna (Italy) (5) Max Planck Institut fuer extraterrestrische Physik (Germany) (6) INAF – Osservatorio Astronomico di Padova (Italy) (7) European Southern Observatory (Germany)
MAORY is the Multi-Conjugate Adaptive Optics (MCAO) module designed to work on the Nasmyth platform of the European Extremely Large Telescope (E-ELT). It relays the telescope focal plane to the science instrument and corrects the wavefront aberrations due to atmospheric turbulence and other disturbances such as telescope windshake. It provides a corrected field of 2 arcminutes on the wavelength range 0.8-2.4 µm. The module performance and design have been optimized for the client instrument MICADO (Multi-AO Imaging Camera for Deep Observations). A second output port to feed another instrument is available. The MCAO module corrects the wavefront using the telescope’s adaptive mirror M4, optically conjugated to the ground layer and complemented by the tip-tilt mirror M5, and two deformable mirrors integrated in the module itself and conjugated to high altitude turbulent layers. The measurement of the wavefront distortions is performed by a suite of 6 Laser Guide Star WaveFront Sensors (LGSWFS) and 3 Natural Guide Star WaveFront Sensors (NGSWFS) for the measurement of the modes which cannot be properly sensed by the LGSWFS. In each NGSWFS probe the light is split in two beams: the longer wavelength light (1.5-1.8 micron) is used for fast sensing of low order modes, exploiting the image shrinking ensured by the MCAO loop, while the shorter wavelength light (0.6-0.9 micron) is used for sensing intermediate order aberrations at slower rate by means of a wavefront sensor with tunable pupil sampling. The MCAO system architecture is based on a robust closed-loop approach, which ensures reliable peak performance as well as good sky coverage. An overview of the module design and of the expected performance is given, addressing in particular the last results on the optical design and on the optimization of the NGSWFS performance closely related to sky coverage.