Return flux measurements of a high-power polychromatic laser guide star

Abstract

Laser guide star (LGS) adaptive optics has become widespread in ground-based astronomy. It is also the most promising approach for countering atmospheric distortions in uplink optical satellite communications and laser-based space debris tracking and maneuvering. The best performance is achieved when the LGS is created in the sodium layer at 90 km altitude. A major shortcoming of the technique is the tip/tilt indeterminacy of the LGS, which requires an additional reference beacon (natural guide star or satellite downlink), limiting sky coverage or the control of uplink beam wander. We report on recent simulations and on-sky experiments exploring the feasibility of a polychromatic LGS, which enables tip/tilt measurement via the differential tilt between two wavelengths emitted by the sodium guide star. For the experiments, we used two state-of-the-art > 50-W laser systems at 589 and 569nm, based on TOPTICA’s second-generation guide star laser platform.