Anisotropic Nonlinear Optical Properties of a SnSe Flake and a Novel Perspective for the Application of All-Optical Switching

The deceptively simple tin selenide (SnSe) film has emerged as an appealing 2D material with a narrow bandgap, high charge carrier mobility, and significant thermoelectric figure of merit. In particular, compared with most commonly investigated 2D materials, SnSe with a puckered honeycomb structure possesses a lower lattice symmetry, resulting in prominent in-plane anisotropy. Herein, with polarization-dependent Raman spectroscopy and polarization-dependent nonlinear absorption measurements, pronounced polarization-dependent nonlinear optical properties of a SnSe flake are demonstrated originating from the anisotropic optical transition probability of SnSe, which is confirmed by ultrafast polarization-dependent pump-probe experiments. Furthermore, a novel SnSe-based all-optical switch is proposed and experimentally explored. Specifically, due to the polarization-dependent nonlinear optical response of SnSe, this all-optical switch can access the ON and OFF modes of continuous-wave signal light (633 nm, 13 mu W) by altering the polarization of the switching light (800 nm, 65 fs, 1 kHz, 34 GW cm(-2)), rather than modifying its intensity, achieving an unexpectedly high ON/OFF ratio (the difference of the normalized transmittance of signal light between ON and OFF modes) of 44%. This work opens up real perspectives for versatile optoelectronic devices based on SnSe materials.