Switching between two Laser Guide Star Facilities: An overview of the opto-mechanical design for the new laser beam injector at the Gemini South Observatory

A motorized laser Beam Injector Module (BIM) has been designed to integrate the new Toptica SodiumStar 20/2 laser to the Beam Transfer Optics (BTO) subsystem of the Gemini South telescope. The main goal is to inject the new laser beam co-axially to the BTO optical axis without altering the optical path of the current Lockheed Martin Coherent Technologies (LMCT) sodium laser. The optical design consists of a custom high-power attenuator offering two power modes, an opto-mechanical laser switch to commute between the two laser guide star facilities within a short period of time and a set of tip-tilt picomotor mirror mounts for BTO optical alignment. The motorized module is remotely controlled via an EPICS command interface by the laser operator that can propagate both lasers consecutively on sky for the measurement of the sodium layer guide star photon return. The laser beam factor quality and optical characteristics of the beam injector output beam have been measured within the Gemini South Laser Guide Star (GS-LGS) requirements. This paper presents a general overview of the new sodium laser facility and the beam injector opto-mechanical design. It reports on the optical calibration, laser beam characterization, telescope integration and BTO optical alignment.