Optimized Seeded-Bridgman Growth and Characterizations of LiGaS2 Crystals

Abstract

Mid-infrared (MIR) nonlinear optical (NLO) crystals are essential for MIR laser generation, playing a crucial role in both civilian and military applications, particularly in high-power ultrafast laser systems. LiGaS2 (LGS) has attracted considerable attention due to its unique combination of a wide transparency window, relatively high nonlinear optical coefficient, high laser-induced damage threshold, and suppressed two-photon absorption under high-intensity excitation, making it especially suitable for ultrafast MIR frequency conversion. However, the growth of large-sized, high-quality LGS crystals remains a significant challenge, which severely limits their practical applications. In this work, high-quality, large-sized LGS crystals (Ø21 mm × 60 mm) were successfully grown using the optimized seeded-Bridgman method.Comprehensive characterizations confirm the high crystalline quality and excellent physical properties of the as-grown crystals. Thermal property investigations revealed that LGS exhibits a maximum thermal conductivity of 12.06 W•m-1•K-1 along the (001) direction at 25 °C. Temperature-dependent photoluminescence (PL) and transient absorption spectroscopy (TAS) reveal the presence and dynamic behavior of defect states, clarifying their impact on optical performance. Furthermore, accurate refractive indices and corresponding dispersion relations were determined, providing essential parameters for phase-matching design in nonlinear optical processes. These results demonstrate that high-quality, large-sized LGS crystals with favorable thermal and nonlinear optical properties can be reliably achieved, providing a solid material foundation for high-power ultrafast MIR laser applications.