Third harmonic generation in monoclinic 2D KNbO3 with high power endurance

Two-dimensional (2D) KNbO3 is prepared by topotactic transition from 2D KNbO2 at 530 °C in air, which has a single spontaneous polarization (Ps) direction along the [101¯]pc zone axis. The strong Ps anisotropy leads to a negligible second harmonic generation of 2D KNbO3 with laser vertically incident on the sample. However, a strong third harmonic generation is observed. The effective third-order susceptibility of 2D KNbO3 with the order of ∼10−19 m2 V−2 is estimated by comparing it with the χeff(3) of graphene. The robust power tolerance of 2D KNbO3 endows it great potential in the application of high-power third harmonic generation 2D devices.