  We demonstrate a high-power narrow-linewidth ultraviolet (UV) laser system at
318.6 nm for direct 6S1/2-nP (n = 70 to 100) Rydberg excitation of cesium
atoms. Based on commercial fiber lasers and efficient nonlinear frequency
conversion technology, 2.26 W of tunable UV laser power is obtained from
cavity-enhanced second harmonic generation following sum-frequency generation
of two infrared lasers at 1560.5 nm and 1076.9 nm to 637.2 nm. The maximum
doubling efficiency is 57.3%. The typical UV laser power root-mean-square
fluctuation is less than 0.87% over 30 minutes, and the continuously tunable
range of the UV laser frequency is more than 6 GHz. Its beam quality factors M2
X and M2 Y are 1.16 and 1.48, respectively. This high-performance UV laser has
significant potential use in quantum optics and cold atom physics.
