High efficiency frequency doubling with a passive enhancement cavity

Highly efficient frequency doubling of a continuous-wave Yb-doped fiber laser with a passively-locked enhancement cavity is achieved. The increase in efficiency is a result of improved transverse mode matching between the fiber and doubling cavities, which is enabled by an alignment method presented here. An optical conversion efficiency as high as 36.8% from a launched 976 nm diode pump to a 532 nm green laser is obtained. The maximum 532 nm output is 24.5 W, which is limited by the onset of parasitic oscillations in the fiber laser.