The laser guide star system for the Giant Magellan Telescope laser tomography adaptive optics

The Laser Tomography Adaptive Optics (LTAO) system for the Giant Magellan Telescope (GMT) will be the first laser guide star adaptive optics (LGS AO) wavefront control for the GMT, aimed at pushing the boundaries of astronomical observations beyond the limits of natural guide star (NGS) operations. The Australian National University is leading the design of some of the largest work packages in the GMT LTAO project, including the GMTIFS on-instrument wavefront sensor, LTAO LGS wavefront sensors, and the Laser Guide Star System (LGSS). Central to the LTAO system is the Laser Guide Star Subsystem (LGSS), responsible for creating a Laser Guide Star (LGS) asterism adjustable between 25 to 60 arcsec and centred on the science target. The LGSS comprises six Laser Guide Star Units (LGSU), each emitting a laser beam with precise spectro-temporal and spatial characteristics. The LGSU includes a Laser System, a Beam Conditioning and Diagnostic System (BCDS), a Laser Launch Telescope (LLT), and a LGS Unit Control System (LGSU CS). These components collectively ensure accurate pointing and focusing of the laser beam on the sky. This paper provides a comprehensive update on the re-assessment and redesign of the LGSS for the GMT, a collaborative effort reignited at the Australian National University after a ten-year hiatus in design work. The LGSS design is ready to re-attain the Preliminary Design level, after integrating interface changes that have evolved at the telescope since the Preliminary Design Review took place in 2013. In order to take advantage of advances made in the field over the past 10 years, the study investigates the feasibility of a shared launch for the GMT LTAO system and also re-evaluates the number of lasers required to generate the 6 LGS asterism.