Tunable Ultrafast Nonlinear Optical Properties of Graphene/MoS van der Waals Heterostructures and Their Application in Solid-State Bulk Lasers.

For van der Waals (vdW) heterostructures, optical and electrical properties ( e.g., saturable absorption and carrier dynamics) are strongly modulated by interlayer coupling, which may be due to effective charge transfer and band structure recombination. General theoretical studies have shown that the complementary properties of graphene and MoS enable the graphene/MoS (G/MoS) heterostructure to be used as an important building block for various optoelectronic devices. Here, density functional theory was used to calculate the work function values of G/MoS with different thicknesses of MoS, and its relaxation dynamic mechanism was illustrated. The results reveal that the G/MoS heterostructure interlayer coupling can be tuned by changing the thickness of MoS, furthering the understanding of the fundamental charge-transfer mechanism in few-layer G/MoS heterostructures. The tunable carrier dynamics and saturable absorption were investigated by pump-probe spectroscopy and open-aperture Z-scan technique, respectively. In the experiments, we compared the performances of Q-switched lasers based on G/MoS heterostructures with different MoS layers. Taking advantage of ultrafast recovery time and good saturable absorption properties, a femtosecond solid-state laser at 1.0 μm with G/MoS heterostructure saturable absorber was successfully achieved. This study on interlayer coupling in G/MoS may allow various vdW heterostructures with controllable stacking to be fabricated and shows the promising applications of vdW heterostructures for ultrafast photonic devices.