VLT 4LGSF laser launch telescope

VLT Four Laser Guide Star Optical Tube Assembly The image quality of ground based telescopes can be significantly improved with the use of Adaptive Optics (AO). The AO system corrects the wavefront distortions introduced by the turbulent atmosphere. The European Very Large Telescope (VLT) is currently being upgraded with a Four Laser Guide Star AO system. TNO builds the Optical Tube Assemblies (OTA) for this Four Laser Guide Star Facility (4LGSF). AO systems require a reference source for wavefront correction. On 10 meter class telescopes, sufficiently bright stars are only available for about 1% of the astronomical targets, therefore the application of natural guide star adaptive optics is very limited. This limitation can be overcome by using an artificial laser guide star. Laser guide stars work by projecting a powerful laser beam to the upper reaches of the atmosphere. The beam excites the sodium atoms in this atmospheric layer at an altitude of 90 km, producing an artificial star in the sky. A wavefront sensor is used to detect how the atmospheric conditions affects the light from the laser guide star. A powerful computer calculates the required real time corrections, which are applied using a deformable mirror with hundreds of small actuators.More info on www.tno.nl/vlt4lgsf