High-Efficiency Second Harmonic Generation of Mode-Locked Picosecond Ti:sapphire Laser Using BiB3O6 Crystal with External Enhancement Cavity

We reported a high-efficiency second harmonic generation (SHG) of a low-power mode-locked picosecond Ti:sapphire laser, whose average output power was less than 1 W, using a BiB3O6 (BiBO) nonlinear crystal installed in an external enhancement cavity. Ultraviolet (UV) coherent light at 389 nm with the maximum average power of 506 mW was obtained with the input average power of 805 mW using the external cavity. Considering the reflective loss of the output coupler of the 389-nm light, we could estimate the intrinsic conversion efficiency of 70%. This value, to the best of our knowledge, is the highest conversion efficiency for SHG using a BiBO crystal, even at the relatively low fundamental power.