The ALFA laser guide star: Operation and Results

The importance of laser guide stars to the practical usefulness of adaptive optics cannot be understated, and yet there are very few working systems. This contribution discusses the current status of the ALFA laser guide star, with regard to the particular difficulties encountered while observing as well as both the expected performance and that so far achieved from scientific observations. A description is given of a number of experiments involving ALFA which aim to determine the atmospheric turbulence and sodium layer charateristics, and demonstrate the possibility for tilt recovery from laser guide stars.