A new nonlinear optical crystal Li0.81Ag0.19InSe2 with balanced properties for efficient nonlinear conversion in the mid-IR region

The achievement of balanced properties among nonlinear optical (NLO) effect, laser induced damage threshold (LIDT) and optical birefringence is the key to obtain the excellent NLO crystals for harmonic mid-IR coherent radiation generation. In this work, we successfully synthesize and grow a new NLO chalcogenide crystal Li0.81Ag0.19InSe2 by utilizing a molecular design strategy with rational replacement between Li and Ag. This crystal not only enlarges the very low birefringence in AgInSe2 from ~ 0.017 to ~ 0.047, but also improves the rather small NLO effect in LiInSe2 from 11.8 pm/V to ~26 pm/V while maintaining the LIDT almost unchanged. Based on the large size Li0.81Ag0.19InSe2 single crystals of optical quality, the spectroscopic properties are measured and the main parameters important for NLO output are determined. All these results demonstrate that Li0.81Ag0.19InSe2 is a promising mid-IR NLO crystal with balanced properties.