LASER GUIDE STAR FOR 3.6- AND 8-M TELESCOPES - PERFORMANCE AND ASTROPHYSICAL IMPLICATIONS

We have constructed an analytical model to simulate the behaviour of a n adaptive optics system coupled with a sodium laser guide star. The c ode is applied to 3.6- and 8-m class telescopes. The results are given in terms of Strehl ratio and full width at half-maximum of the point spread function. Two atmospheric models are used, one representing goo d atmospheric conditions (20 per cent of the time), the other median c onditions. Sky coverage is computed for natural guide star and laser g uide star systems, with two different methods. The first one is a stat istical approach, using stellar densities to compute the probability o f finding a nearby reference. The second is a cross-correlation of a s cience-object catalogue and the USNO catalogue. Results are given in t erms of percentage of the sky that can be accessed with given performa nces, and in terms of the number of science objects that can be observ ed, with Strehls greater than 0.2 and 0.1 in the K and J bands.