Generation of Continuous-Wave 194 nm Laser for Mercury Ion Optical Frequency Standard

A 194-nm cw laser is an essential part in the mercury ion optical frequency standard. We report the generation of over 2 mW continuous-wave radiation at 194 nm in a beta barium borate crystal using a simple sum frequency mixing (SFM) system. One source beams at 718 nm is resonantly enhanced with a cavity and the other at 266 nm makes a single pass. Considering the walk-off effect in SFM, the source beam waists are designed to be elliptical, thus the conversion efficiency can be promoted. The 266-nm beam produced by frequency doubling of 532-nm laser is shaped close to the diffraction limit to achieve better mode matching.