Nonlinear optical modulation of MoS2/black phosphorus/MoS2 at 1550 nm

A sandwich structure of black phosphorus nanosheets coupled with MoS2 nanosheets was prepared via liquid exfoliation and hydrothermal methods. An enhancement of saturated absorption was observed at the long wavelength of 1550 nm via the femtosecond Z-scan technique, which is much stronger than its nonlinear response at 400 and 800 nm. According to the ultrafast pump-probe results, this strong saturated absorption can be attributed to the dominant role of a slow relaxation process, corresponding to the enhanced interface and defects effects. Moreover, the nonlinear refractive properties were found to transform from self-focusing to self-defocusing with the increasing of excitation wavelength from visible to near-infrared region, which can be qualitatively explained by an effective medium approach, similar to noble metal nanomaterials. These results suggest that the synthesized MoS2/BP/MoS2 may have potential applications for nonlinear optical devices.