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

Abstract 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 µW) 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.