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Low Order modes retrieval for LGSs tomography

Abstract 134

Submitted by Simone ESPOSITO


S. Esposito (1), P.M. Gori (1), L. Busoni (1), G. Brusa (2)


(1) Osservatorio di Arcetri; (2) Large Binocular Telescope Observatory


Most of the planned MCAO systems for astronomical telescopes uses laser beacons to create at will a star constellation having the geometry required for a good tomographic reconstruction. The LGS tip tilt indetermination problem does not allow to measure the tilt of the reference sources. As a consequence the global tilt of the NGSs over the FoV and altitude and amplitudes of the low order modes are not correctly estimated. To solve these problems, in general, several NGSs are used. However the use of a few NGSs can reduces the sky coverage of the LGS MCAO system by a significant factor. In this paper we present a technique to estimate the low order modes tomographic distribution directly from the LGSs. In this scheme only one NGS is still needed to measure the global tilt over the FoV. In this way the sky coverage of the MCAO system is improved. The paper reports the performance of this technique for both 8m and 42m telescope diameter cases calculated with numerical and analitical simulations.

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