Strong anisotropic third-harmonic generation in layered violet phosphorus

We demonstrate that layered violet phosphorus, an emerging 2D semiconductor, undergoes strong anisotropic third-harmonic generation (THG). Polarization dependence of in-plane THG presents a cruciate-flower-shaped curve. Through theoretical modeling of the in-plane THG response, done by considering crystalline symmetry of violet phosphorus, we successfully quantify four non-zero third-order nonlinear optical susceptibility tensor elements. From control experiments, the magnitude of third-order nonlinear optical susceptibility |chi 3| is calculated to be about 4.0 x 10-19 m2 V-2, which is comparable to those of conventional 2D layered semiconductors. These results indicate that the layered violet phosphorus can serve as an ideal building block for nonlinear optical applications. Strong third-harmonic generation (THG) is observed in layered violet phosphorus (VP). Polarization-resolved THG reveals its anisotropic, nonlinear optical response, which can be utilized to determine the lattice orientation optically.