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 2mW 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 Emit to achieve better mode matching.