AlGaS3: A Wide Band Gap Ternary Diamond-Like Infrared Nonlinear Optical Material with High Laser-Induced Damage Threshold
Infrared nonlinear optical (IR NLO) materials are critical for laser frequency conversion, yet their performance is often constrained by a trade-off between second harmonic generation (SHG) efficiency and laser-induced damage threshold (LIDT). Here, we report a new ternary diamond-like compound, AlGaS3, which successfully balances these competing demands. AlGaS3 crystallizes in a noncentrosymmetric structure composed of wide HOMO-LUMO gap [AlS4] tetrahedra and NLO-active [GaS4] tetrahedra. The compound exhibits a wide experimental optical band gap of approximately 3.38 eV, which is significantly larger than that of the benchmark AgGaS2 (AGS, ~2.70 eV). This wide band gap contributes to a high laser-induced damage threshold (LIDT) of approximately 6.0 times that of AGS, as determined by powder-based measurements. Notably, AlGaS3 also demonstrates a phase-matching SHG response of approximately 0.5 times that of AGS at a fundamental wavelength of 2.09 μm, with particle size-dependent behavior confirming phase-matchability. The combination of wide band gap, high LIDT, and moderate SHG response positions AlGaS3 as a promising candidate for high-power IR NLO applications. This work provides a viable strategy for designing IR NLO materials with enhanced laser damage resistance by incorporating wide-gap tetrahedral units.