Ultrafast saturable absorption of MoS_2 nanosheets under different pulse-width excitation conditions

Abstract

The newly raised two-dimensional material MoS₂ is regarded as an ideal candidate for saturated absorbers. Here, the open-aperture Z-scan method is used to study the saturation absorption (SA) response of monolayer and multilayer MoS₂, considering laser irradiation with different pulse widths. Specifically, in cases of 10 ns and 10 ps laser pulses, the accumulative nonlinearity [e.g., free carrier absorption (FCA)] coupled with SA is found in both monolayer and multilayer MoS₂. However, under a 65 fs pulse laser, the instantaneous nonlinearity [e.g., two-photon absorption (TPA)] and the SA effect turn to play a significant role. Additionally, the saturation of both TPA and FCA is observed in MoS₂. Importantly, the modulation depth of MoS₂ shows different change trends by adjusting the laser pulse width.