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, and 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.