Laser guide star experiment at Lawrence Livermore National Laboratory

An overview of the Laser Guide Star feasibility experiment at Lawrence Livermore National Laboratory is presented. The goal of the project is to demonstrate a closed-loop adaptive optics system using a sodium-layer laser guide star to correct wavefront aberrations caused by atmospheric turbulence. The laser beam is projected upwards from a beam director located 5 meters from a half-meter telescope and forms a spot about 2 meters in diameter in the mesospheric sodium layer at an altitude of about 95 km. The laser beam is approximately fifth magnitude and is visible to the unaided eye at the top of the Rayleigh-scattered laser beam. A Shack-Hartmann wave front sensor measures the aberrated wave front and a continuous sheet deformable mirrow will correct the wave front in a closed loop control system at a bandwidth fast enough to follow changes in the atmosphere. In this paper, the authors present an overview of the methodology for the design of the experiment and the requirements of the laser source. The long term goal of this effort is to develop laser guide stars and adaptive optics for large astronomical telescopes and to this end, a summary of laser issues relevant to future sites is presented.