First principles selection and design of mid-IR nonlinear optical halide crystals†
The optical properties of several distinct series of nonlinear optical (NLO) halide crystals with potential applications in the mid-infrared (mid-IR) spectral region have been investigated systematically using a first-principles computational methodology. The crystals have different NLO-active units [MXk] (M = center cation, X = halide anion, and k = 6, 4, 3 or 2) and by combining atomic-level analysis with optical design considerations, their prospects for mid-IR applications are evaluated. The preferred microscopic structural units, which result in a relatively large NLO response and high laser damage threshold, are proposed. The study provides first principles guidance in the selection and design of novel halide crystals for mid-IR NLO applications.