Alternative Methods for Creating a Sodium Laser Guide Star

The objective of the proposed effort is to demonstrate robustly-engineered stable vertical-external-cavity surface-emitting laser (VECSEL) sources of 20 W at 589 nm and 10 W at 1141 nm with narrow linewidth matched to a single velocity class of mesospheric atomic sodium for guide star application. A scalable architecture is realized by employing multiple VECSEL devices in one resonator, thus allowing high saturated output power. A critical output of Phase I was the demonstration of the “twisted-mode� cavity configuration which stabilizes the standing wave pattern in a resonator with multiple resonant periodic gain structures. In this arrangement, the antinode of the standing wave pattern always matches the location of the quantum wells which provide optical gain and ensures single-frequency operation. In Phase II, the prototype 1178 nm device will be optimized for power, with the addition of further VECSEL devices, an external doubling cavity will be added to convert the output to 589 nm, and the 1141 nm device will be constructed using VECSEL devices already in hand. Both lasers will be engineered for deployment to a telescope. The 589 nm laser will be demonstrated on sky at a 1.5 m telescope.