Preliminary design of the Laser Guide Star Facility for the ULTIMATE-Subaru Ground Layer Adaptive Optics system

The Ground Layer Adaptive Optics (GLAO) system for ULTIMATE, the next generation instrumentation project for the Subaru telescope, will generate and use four laser guide stars on sky in side-launch configuration. The design of the GLAO is led and coordinated by the Subaru telescope in collaboration with Tohoku University, Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), and the Australian National University (ANU). ANU is responsible for the wavefront sensor subsystem and the Laser Guide Star Facility. The GLAO Laser Guide Star Facility (LGSF) includes two Sodium guidestar lasers to be split in a total of four, generating an asterism of four artificial stars on the Hawaiian skies. Divided into three main subsystems (beam transfer optics, beam diagnostics, and beam projection), the GLAO LGSF accounts for the conditioning, splitting, and steering of the laser beams as well as for their launching configuration over a patrol field of 20 arcmin on sky. This paper presents the preliminary design of the GLAO Laser Guide Star Facility including different approaches for the most efficient splitting of the guidestar lasers, and specifications summary for the final selection of the laser launch telescopes.