High efficiency extra-cavity frequency conversion UV laser

High efficiency extra-cavity third harmonic generation (THG) of 355 nm beam has been developed. A laser diode（LD） end-pumped, acoustic optical Q-switched Nd:YAG laser was used as the fundamental wave source. With an input pump power of 25 W, the average power of 6.2 W at 1 064 nm was generated with the repetition rate of 12 kHz. Using the extra cavity frequency conversion of three critical phase match LiO3O5 (LBO) crystals, 2.7 W third harmonic radiation at 355 nm was obtained. The optical to optical (1 064 nm to 355 nm) conversion efficiency was up to 43.5%．