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Over the last 30 years, Sodium Guidestar Lasers (SGLs) have proved to be an important element of adaptive-optics (AO) image correction techniques for astronomical observatories. In recent years, the astronomy community has employed Raman shifted fiber lasers to meet the need. However, emerging applications would greatly benefit by a reduction in the cost per Watt of on-sky power and the Size Weight and Power (SWAP) required by the laser. Small (meter-class) observatories seek to incorporate AO systems to meet space situational awareness and free space laser communication applications. Simultaneously, large (10 meter class) observatories require larger numbers of lasers on-sky to implement multi-conjugate AO systems, Further, techniques such as re-pumping and frequency-chirping are being developed to increase returns from the sky for a given laser power. The next generation of SGLs (Sodium Guidestar Lasers) must be suited for such modes of operation while reducing cost and SWAP. Optically pumped semiconductor lasers (OPSLs), also referred to as Vertical External Cavity Surface Emitting Lasers (VECSELs), represent a technology pathway to realizing SGLs with high performance, compact size, high reliability, and low acquisition and maintenance costs. In pursuit of the next generation of SGL, we demonstrate 8W of single-frequency power at 589 nm based on in intracavity frequency doubling of 1178 nm fundamental wavelength VECSEL. Our work investigates the key challenges of the laser design; especially frequency selection, tuning, and locking the laser to sodium resonance, laser power, and gain-mirror lifetime. |
