Nonlinear Optical Absorption of ReS2 Driven by Stacking Order

The stacking order of 2D materials can result in fascinating physical properties. Two different stacking orders (AA and AB) were recently identified in ReS2, a rising star in the transition metal dichalcogenides family with a unique anisotropic property. Their optical and vibrational properties show drastically different features. With intensity-scan spectrometry, the nonlinear optical absorption of both AA and AB stackings in ReS2 was investigated. Saturable absorption (SA) only occurs in AB stacking at certain polarization angles, whereas it is absent in AA stacking. This saturation behavior is attributed to strong exciton–exciton annihilation (EEA). Excited-state absorption (ESA) is prominent in both stacking orders, but more anisotropic with polarization in AB stacking. Our results provide new insights in using ReS2 as a nonlinear optical material in forefront optoelectronics.