High-power, single-frequency intracavity doubled VECSEL at 589 nm for sodium guide stars

Sodium Guidestar Lasers (SGLs) are 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. Optically pumped semiconductor lasers (OPSLs), also referred to as Vertical External Cavity Surface Emitting Lasers (VECSELs), represent a technology pathway to realizing Sodium Guidestar Lasers (SGL)s with high performance, compact size, high reliability, and low acquisition and maintenance costs. In pursuit of the next generation of SGL, we demonstrate <15W of single-frequency power at 589 nm based on in intracavity frequency doubling of 1178 nm fundamental wavelength VECSEL. Our work characterizes laser performance with an emphasis on suitability for guidestar laser applications. We examine, wavelength stability, linewidth, tuning and tuning agility and the ability to lock the laser to the sodium transition. In addition, we demonstrate simultaneous generation collinear beams with a frequency spacing of approximately 1.7 GHz.