Cavity-enhanced deep ultraviolet laser for two-photon cooling of atomic hydrogen.

We demonstrate a 650 mW 243 nm continuous-wave laser coupled to a linear optical enhancement cavity. The enhancement cavity can maintain >30  W of intracavity power for 1 h of continuous operation without degradation. This system has sufficient power for a demonstration of two-photon laser cooling of hydrogen and may be useful for experiments on other simple two-body atomic systems.