SODIUM BEACON TIP-TILT DETERMINATION WITH RAYLEIGH-AIDED AUXILIARY TELESCOPE TECHNIQUE

The usefulness of tracking the Rayleigh portion of a mesospheric sodiu m laser guide star as reference for absolute tip-tilt recovery in the frame of the auxiliary telescopes technique is shown. This approach le ads to the reduction of the ground occupation needed to attain a given sky coverage by more than one order of magnitude. Speed, tracking pre cision, and the number of auxiliary telescopes are also reduced, makin g this new approach a more attractive one. The use of a low-altitude R ayleigh spot reinforces the fundamental limitations affecting this and other techniques, thus degrading significantly the quality of the rec overed tip-tilt. However, it is shown that, provided adequate care is taken in the collection and treatment of data, an interesting tilt sig nal can still be retrieved.