Development and demonstration of a VECSEL based sodium guidestar system

Sodium Guidestar Laser Systems (SGLS) have been used in conjunction with Adaptive Optics (AO) to improve seeing in astronomical observatories for more than 30 years. Adaptive optics allow ground-based imagers to overcome atmospheric distortion-limited observation by using natural and artificial guide stars to measure the distortion. Sodium-layer guide stars provide near all-sky coverage for high resolution astronomy. In this paper the authors discuss the development of a VECSEL based SGLS and installation and on sky demonstration of the system at UCO Lick’s Shane Telescope. The system comprises a compact, high-power, single-frequency VECSEL tuned to sodium resonance which is coupled to a Hollow Core Fiber to transport the laser light to the launch telescope and includes diagnostic and control subsystems. The novel SGLS discussed here is sufficiently compact and robust to mount directly to and operate on the Shane telescope support structure. Cooling water, power, and electronic signals are routed from a separate enclosure, though in future efforts those can be included on the structure too. The SGLS has been developed over the last five years and preliminary results presented at previous sessions at Photonics West. This paper addresses system configuration and laboratory performance measurements, telescope installation (September of 2025) and on-sky tests of sodium photon return performance. The VECSEL SGLS provides the ability to generate both the D2a and D2b lines to enable repumping of the sodium transition and thus produce brighter stars. Measurements of spot size, star brightness as a function of D2a and D2b power, and polarization are discussed.