Crystal Growth and Property Characterization of a Novel Long-Wave Infrared Nonlinear Optical Crystal BaHgGeSe₄

BaHgGeSe4, a long-wave infrared nonlinear optical crystal, is very interesting due to its broad transmission range and substantial nonlinear optical coefficient. However, there have been no reports on its bulk crystal growth yet. This study thoroughly investigates the large-scale polycrystalline material synthesis and crystal growth of large BaHgGeSe4 crystals. By utilizing high-temperature and high-pressure methods, we successfully synthesized 100 g of BaHgGeSe4 polycrystalline material in a single batch. Furthermore, by increasing the temperature gradient within the furnace and enhancing the degree of undercooling, we successfully grew a BaHgGeSe4 single crystal with dimensions of Φ35 × 36 mm3 using the Bridgman method. The crystal exhibits a (400) peak rocking curve fwhm of about 0.025° and a transmittance of around 52% over a wide range of 1–15 μm. Additionally, the surface laser damage threshold was measured to be 530 MW/cm2 using a Nd:YAG (1064 nm) laser under conditions of 5 ns pulse width, 1 Hz frequency, and D = 0.12 mm spot size.