The Giant Magellan Telescope laser tomography adaptive optics system

Abstract

The Giant Magellan Telescope presents a unique optical design with seven 8.4 m diameter primary mirrors matched by seven adaptive secondary mirrors (ASM). The ASMs can be controlled in several dierent Adaptive Optics (AO) observing modes coupled to the telescope . One of these AO systems, the Laser Tomography Adaptive Optics (LTAO) system is currently in its preliminary design phase. The LTAO observing mode will provide a Strehl ratio in H band of at least 30% over more than 20% of the sky and an ensquared energy in K band of at least 40% in a 50 milli-arcsec spaxel over more than 50% of the sky. To achieve its performance requirements, the LTAO observing mode uses six 20W Laser Guide Stars (LGS) with six order-60x60 Shack-Hartmann wavefront sensors. The LGSs are launched from three locations at the periphery of the telescope primaries. A natural guide star (NGS) is used separately to measure tip-tilt, focus and low-bandwidth-low-order aberrations, as well as telescope segment piston. An open-loop controlled deformable mirror corrects the o-axis NGS infrared wavefront. We give an update on the design of the LTAO WFSs, the LGS facility, the on-instrument wavefront sensors and the tomography and control algorithms.