Laser technologies for laser guided adaptive optics

The principles of the laser guide star (LGS) for adaptive optics (AO) are described, as well as the physical processes involved in their generation. System design issues are addressed, such as laser spot elongation and brightness. The two main families of LGS, based either on Rayleigh or sodium resonant scattering are discussed in terms of performances and of laser technologies required to match requirements. LGS aided AO systems built for astronomical telescopes are described, with a special emphasis for the Lick and Keck systems which are the only ones in routine operation for science. The future 30-100 m telescopes need an intense R&D program for a new generation of robust turn key lasers. These lasers must be compact, have nearly diffraction limited beam quality with 10 to 50 W output at 589 nm.