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We demonstrate a 1.4 W continuous-wave (CW) laser at 243.1 nm. The radiation is generated through frequency quadrupling the output of a ytterbium-doped fiber amplifier system. which produces >10  W of CW power at 972.5 nm. We demonstrate absolute frequency control by locking the laser to an optical frequency comb and exciting the 1S−2S transition in atomic hydrogen. This frequency-stabilized, high-power deep-UV laser is of significant interest for precision spectroscopy of simple and exotic atoms, two-photon laser cooling of hydrogen, and Raman spectroscopy.

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.