Recent progress on sulfide infrared nonlinear optical materials with large SHG response and wide band gap

As the core device of all-solid-state laser, infrared (IR) nonlinear optical (NLO) material plays a critical role in exploring new coherent lights by frequency conversion technologies, which are widely used in noninvasive medical diagnostics, spectroscopy, environmental monitoring and long-distance laser communication. To satisfy the growing demand of current laser technology in IR regions, high performance NLO materials with large second-harmonic generation (SHG) response, high laser-induced damage threshold (LIDT) and wide transparency range are highly expected. Recently, numerous efforts and advances have been achieved in sulfide system. This review highlights the progress of high-performance sulfide IR NLO materials with a good balance between strong SHG response (>= 1.0 x AgGaS2) and wide band gap (>= 3.0 eV) since 2018. The chemical synthesis, crystal structure, optical properties and structure-property relationship of 13 high performance metal sulfide IR NLO materials are summarized and reviewed in detail. Finally, the potential opportunities and challenges in IR NLO materials are discussed.