Recent Advances in Oxide-based Nonlinear Optical Materials with Wide Infrared Transparency Beyond 6 μm.

Nonlinear optical (NLO) materials are indispensable for laser frequency conversion, by which the output wavelength of laser can be greatly expanded. A prerequisite for the applications of NLO materials is that they must be optically transparent in the working spectral range. Although the widely used infrared (IR) NLO crystals such as AgGaS2 , AgGaSe2 , and ZnGeP2 have very broad mid-IR (2-20 μm) transparency, they are all inherently suffered by low laser-induced damage thresholds (LDTs). Oxide-based materials usually possess desirably high LDTs, however, most of them have quite limited IR transparency, typically, within 6 μm. In this Minireview, we focus on new oxide-based NLO materials showing exceptionally wide IR transparent ranges beyond 6 μm, in which significant developments have been achieved in recent years. Nine relevant NLO materials are investigated and analyzed from the aspects of design strategy, synthesis and large crystal growth, optical and NLO properties as well as composition-structure-property correlations. A brief perspective on the future research directions is also provided.