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

A sandwich structure of black phosphorus nanosheets coupled with MoS 2 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 MoS 2 /BP/MoS 2 may have potential applications for nonlinear optical devices .