Zinc germanium phosphide (ZnGeP₂, ZGP) is known as one of the most promising materials for nonlinear optical applications due to large nonlinear coefficient and high laser damage threshold. A high optical quality ZnGeP₂ single crystal of 50 mm in diameter was successfully grown by the vertical Bridgman technique. The OPO devices were fabricated from ZGP crystal as shown in Fig.1. The absorption coefficient of ZGP OPO devices for o-polarized 2 μm light incidence was significantly reduced to 0.02 cm^-1 by thermal annealing and high energy electron irradiation (Fig2.). Moreover, improvement to the polishing of ZGP OPO devices (Fig.3) resulted in an increased laser-induced damage threshold. The value was increased to 2.0 J/cm² at 2.05 μm and 10 kHz pulse rate frequency. As a result, the maximum output of 20.5 W was obtained by high pulse repetition frequency Ho:YAG laser emitting at 2.09 μm under a pump power of 46W. The corresponding slope efficiency was 68.7% and the conversion efficiency was 44.3% (Fig.4). These results manifested the large crystals with high optical quality are acceptable for the fabrication of the infrared nonlinear OPO devices.

Fig. 1 ZGP-OPO devices

Fig.2 Optical absorption coefficient for o-light

Fig.3 Patterns of roughness and flatness

Fig.4 Output power and slope efficiency

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1. Vertical Bridgman Growth of Large ZnGeP₂ Single Crystals for High Power Applications
2. Investigation of Defects in ZnGeP₂ Single Crystals by X-ray Topography on Base of Borrmann Effect
3. The Analysis of Defects in ZnGeP₂ Single Crystals from Birefringence Images
4. Bulk Growth ZnGeP₂ crystals and their Study by X-Ray Topography