Second-harmonic generation of mode-locked Nd:YAG and Nd:YLF lasers using LiB3O5

Acousto-optically mode-locked cw Nd:YAG and Nd:YLF lasers have been efficiently frequency doubled with noncritically phase-matched lithium triborate. LiB3O5 crystals from 6 mm to 15 mm in length were obtained from Castech, People's Republic of China. These were polished and coated for antireflection at both 1064 nm and 532 nm by Coherent Components Group, Auburn, Calif. The coating has a damage threshold in excess of 1 GW/cm2 for mode-locked pulses. More than 11 W of average power at 532 nm has been generated by single pass conversion for a 25 W input at 1064 nm, a conversion efficiency of greater than 45%. Second harmonic generation dependence on laser power and focusing, and on crystal length and temperature have been measured and modeled. Stable longterm operation and applications for high power modelocked 532 nm laser pulses are discussed.