The Giant Magellan Telescope Laser Tomography Adaptive Optics System

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 different 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 off-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.