Broadband studies of the strong mid-infrared nonlinear optical responses of KPSe₆

One-dimensional noncentrosymmetric KPSe₆ is an excellent mid-infrared (mid-IR) nonlinear optical (NLO) material possessing reversible phase-change behavior. In this special issue we present a broadband NLO study on its crystalline and glassy phases as well as fundamental material characterizations. The compound has a bandgap of ~ 2.1 eV and exhibits intrinsic second harmonic generation even in the glassy phase. The crystalline compound is type-I phase-matchable and shows strong second- and third-order NLO responses over a broad wavelength range (1.0-3.0 μm) with excellent optical transparency. Based on the measured NLO coefficients χ⁽²⁾ ≲ 142.8 pm/V and χ⁽³⁾ ≲ 4.7 × 10⁵ pm²/V², we propose that KPSe₆ can be utilized for numerous mid-IR NLO applications.