Microscopic optical nonlinearities and transient carrier dynamics in indium selenide nanosheet

This work systematically investigates the third-order nonlinear optical (NLO) properties and ultrafast carrier dynamics of layered indium selenide (InSe) obtained by mechanical exfoliation (ME). The two-photon absorption (TPA) effect of layered InSe was tested using micro-Z/I-scan techniques. The results indicate that InSe flakes undergo the TPA response under the excitation of both 520 nm and 1040 nm fs pulses, and that InSe is more likely to achieve TPA saturation under visible light excitation. Furthermore, ultrafast carrier dynamics revealed that InSe flakes in the visible region undergo a transition from photoinduced absorption to photobleaching and exhibit a fast recombination time of ∼0.4-1ps, suggesting a high optical modulation speed as high as ∼1-2.5 THz.