Numerical simulation and modified Bridgman growth of high-quality and large-sized LiGaS2 mid-infrared optical crystals

Abstract

Mid-infrared (MIR) ultrafast lasers, generated through nonlinear frequency conversion using nonlinear optical (NLO) crystals, play a critical role in various fields, including ultrafast dynamics and biomedical applications. LiGaS₂ (LGS) crystals are highly promising due to their broad band transparency, high thermal conductivity, high laser damage threshold and high chemical stability, which minimizes two-photon absorption under pump lasers. However, achieving high-quality LGS crystals via the Bridgman method is challenging due to lithium's corrosiveness and sulfur's high vapor pressure at growth temperatures. To obtain high-quality LGS crystals, numerical simulations were conducted to optimize the Bridgman growth process, including the optimal temperature field and growth parameters. Using the optimized Bridgman technique with spontaneous nucleation, high-quality LGS single crystals were successfully grown with dimensions of Ø12 mm × 30 mm. The crystal exhibits a UV absorption edge at 318 nm (optical bandgap 3.90 eV), an infrared cutoff at 12.8 μm, high transmittance (up to 80%) in the 0.4–8.6 μm wavelength range, and excellent crystallinity with a full width at half-maximum (FWHM) of 36′′ in the rocking curves. This work establishes a versatile strategy utilizing numerical simulation-guided optimization for the successful growth of high-quality ternary MIR chalcogenides via the Bridgman method.