Robust Tilt Determination from Laser Guide Stars Using a Combination of Diierent Techniques

The techniques proposed in the literature for the Laser Guide Star absolute tilt determination suuer from some limitations, due to fundamental reasons and/or to practical aspects. A combination of two techniques is proposed here: the tri{static (Belen'kii 1995; Ragazzoni 1996a) and the auxiliary telescope (Ragazzoni, Esposito & Marchetti, 1995) conngura-tions leading to a solution where two auxiliary laser projectors are located in the neighborhood of the main observatory. The laser stripes are used to link the scientiic target to two natural guide stars (with no constraints on their location) allowing a complete recovery of tip{tilt information. In this way a robust, whole sky coverage, approach is obtained. Moreover, a combination with the Double Adaptive Optic technique (Rigaut & Gen-dron, 1992) can further reduce the required displacements of the auxiliary projectors.