Subaru Laser Guide Star System Upgrade and On-sky Characterization

Abstract

The Subaru laser guide star system has been upgraded by implementing the TOPTICA/MPBC guide-star laser and a new mirror-based laser relay system. The upgrade is to replace the aged laser and its transfer system and provide the improved performance for stable science operation. The increased laser return photon can also bring a new capability of generating multiple laser guide stars (LGSs) by splitting the laser beam. The new laser guide star system was installed on the Subaru telescope in December 2021 and commissioning observations were conducted in 2022. The LGSAO mode with the new laser guide star system has been offered for science open use program since 2023. The new laser guide star system provides more stable LGS than the previous system with respect to the laser power and pointing. The LGS spot size is ∼1.0 arcsec in FWHM under median seeing condition. The LGS photon return is more than 10 times brighter than the previous system. By utilizing the increased brightness, further upgrade of the Laser Launching Telescope (LLT) is being implemented to generate the asterism of four LGSs with the diameter variable between 10 and 40 arcsec for the new Laser Tomography Adaptive Optics (LTAO) system.