Fig. 1. (a)–(d) Optical microscope and AFM characterization of both CVD and ME MoS2 monolayers. (e) Raman spectra imply that there are more defects in the CVD MoS2 monolayer than in the ME one. (f) Steady PL spectra were measured, and strong PL quenching was observed in the CVD monolayer. (g), (h) The PL lifetime of an exciton in CVD and ME monolayers was measured using a streak camera.

Fig. 2. Schematic diagram of the setup of the micro-intensity scan.

Fig. 3. (a) Schematic structures of monolayer MoS2 and vacancies in it. SV, sulfur vacancy; MoV, molybdenum vacancy. (b) Energy levels in CVD and ME MoS2, optical transition, and defect-induced fast carrier capture processes (TPA, two-photon absorption; OPA, one-photon absorption). (c) Nonlinear transmittance versus incident pulse peak irradiance for MoS2 monolayers. The solid lines are the fitting results obtained by numerically solving Eq. (1). Inset: the values of the TPA coefficient and corresponding saturation intensity.

Fig. 4. (a), (b) Differential intensity (ΔI/I0) distribution of the output pulse under the same excitation intensity of 300GW/cm2 in 1L, 50L, and 100L CVD and ME MoS2, respectively. (c) Optical limiting performance.