High-power narrow-band mode-locked sodium laser via double-stage sum-frequency generation

A high-power, narrow-band, mode-locked sodium D(2a)laser with a high sum-frequency efficiency is demonstrated by mixing actively mode-locked Nd:YAG 1064 and 1319 nm lasers in two LiB3O5(LBO) crystals. The mode-locked lasers at 1064 nm (23.02 W output) and 1319 nm (17.98 W output) are generated from two diode, side-pumped, Nd:YAG, master oscillator power amplifier laser systems. A macro-micro pulse sodium beacon laser with a 30.2 W output power, 0.3 GHz (0.3 pm) linewidth, and a beam quality given by M-2= 1.23 is obtained with a conversion efficiency of 73.6%. Compared with a single LBO crystal, the sum-frequency efficiency is enhanced by 14.5%. A laser coupled amplitude equation model, including the acousto-optic mode-locker, is applied for theoretical and numerical analyses of the sum-frequency conversion efficiency. The experimental results agree well with the theoretical calculations.