High-repetition-frequency, high-energy mid-infrared ZnGeP2 MOPA system with beam quality improvement

A high-repetition-frequency and high-energy ZnGeP2 master oscillator power amplifier (ZGP-MOPA) system was demonstrated. The pump source was a 2097 nm Ho:YAG laser with average power of about 140 W and repetition frequency of 2 kHz. Using this pump source, the ZGP-MOPA system obtained a mid-wave infrared laser with a maximum power of 58.9 W and pulse width of 20.1 ns, corresponding to the pulse energy of 29.5 mJ. Under the condition of high thermal effect and high gain, the phenomenon of signal and idler beam waist separation was found in the process of measuring OPA beam quality. By adjusting the divergence of OPA seed source to match the divergence of pump source, the beam waist separation of signal and idler was reduced from 400 mm to 200 mm, the beam quality factor M2 of the ZGP-OPA was improved from 5.1 × 4.9 to 3.9 × 3.7(Horizontal directions × Vertical directions), the M2 of the signal was 2.7, and the M2 of the idler was 2.8.