Development of a High-Energy Picosecond Mid-Infrared Laser Based on ZnGeP₂ Optical Parametric Generator/Amplifier

We developed a high-energy picosecond mid-infrared laser based on ZnGeP₂ (ZGP) optical parametric generator (OPG)/optical parametric amplifier (OPA), operating at a pulse repetition frequency (PRF) of 1 kHz. The laser system was equipped with a 2.09 μm high-energy picosecond laser amplification system as the pump source. The pump source itself incorporated a gain-switched laser diode (GSLD) as the seed. By employing a holmium:yttrium-aluminum-garnet (Ho:YAG) regenerative amplifier (RA) and multi-stage power amplifiers, we successfully achieved a maximum pulse energy of 26.2 mJ at a wavelength of 2.09 μm. Initially, using a ZGP OPG and a one-stage OPA, we achieved mid-infrared laser output of over 6.4 mJ. However, the corresponding beam quality deteriorated, with beam quality factors (M²) exceeding 50 in both the x and y directions. To mitigate this issue, we transitioned to a ZGP OPG coupled with a two-stage OPA configuration, resulting in a mid-infrared laser output of over 6 mJ, accompanied by improved beam quality factors of 17.2 and 14.7 in the respective directions. Notably, the overall optical-to-optical conversion efficiency (OOCE) of the system surpassed 40%, with the second-stage OPA demonstrating an impressive OOCE exceeding 45%.