Polarization-Dependent Nonlinear Optical Responses of CrPS4 for Ultrafast All-Optical Switches

Due to the extraordinary chemical and physical properties, ternary chalcogenides with wide-range bandgap, unique structures, and exceptional photoelectric properties have attracted great interest recently. Among them, Chromium thiophosphate (CrPS₄) is a promising semiconductor with excellent optical, mechanical, and electronic properties and has a lower lattice symmetry resulting in significant in-plane anisotropy. Here, the polarization-dependent nonlinear optical (NLO) responses of CrPS₄ flake are investigated. Based on polarization-resolved Raman spectroscopy, which identifies the crystal axis of sample, the anisotropic linear absorption spectra, I-scan technique, and pump-probe measurements are utilized to investigate the optical absorption information of CrPS₄. The polarization-dependent NLO responses are found originating from the anisotropic optical transition probability. And the polar optical phonons play an important role in carrier relaxation processes. Furthermore, CrPS₄-based all-optical switches are proposed, which can modulate the transmittance of signal light (CW laser) by changing the polarization of switch light (fs laser). This work provides insights into polarization-dependent CrPS₄-based devices, which is important to promote the potential applications in optical modulator, versatile optoelectronic detection, and so on.