High-Efficiency Nanosecond Green Laser Based on Extra-Cavity Second-Harmonic Generation of a Nd:YAG MOPA System

A high infrared-to-green conversion efficiency laser is demonstrated by extra-cavity frequency-doubling of a master oscillator power amplifier (MOPA) laser. The oscillator is a diode-side-pumped acousto-optic Q-switched Nd:YAG laser at 1064 nm with an average output power of 38.2 W and a beam quality factor M² = 1.15, operating at a 2 kHz repetition rate and a 38.3 ns pulse duration. After a dual-rod double-pass amplifier, the fundamental seed power is amplified to 89.4 W with the beam quality of M² = 1.41 and pulse duration of 56.4 ns. Using a type I lithium triborate (LiB ₃ O ₅ , LBO) crystal for second-harmonic generation (SHG), an average power of 67.4 W at 532 nm is generated with a beam quality factor of 1.31, operating at 41.8 ns of pulse duration. The corresponding frequency doubling efficiency is as high as 75.4%, which is, to the best of our knowledge, the highest doubling efficiency reported ever for 532 nm source by an extra-cavity SHG laser system.