Ultrafast optical nonlinearity in natural van der Waals heterostructure nanosheets of franckeite

•The franckeite nanosheets show wavelength- and intensity-dependent nonlinear absorption characteristics.•The franckeite nanosheets exhibit ultrafast carrier dynamic process.•The stable femtosecond pulse has been delivered successfully modulated by the ultrafast optical nonlinearity in franckeite nanosheets. Franckeite, a natural van der Waals heterostructure with excellent physicochemical characteristics, has shown great potential for high-performance optoelectronic device. Here, the few-layer franckeite nanosheets have been prepared by liquid phase-exfoliation method successfully, and the nonlinear optical absorption and carrier dynamics behaviors of the nanosheets have been studied experimentally. The franckeite nanosheets show wavelength- and intensity-dependent nonlinear absorption characteristics, and exhibit ultrafast carrier dynamic process. The ultrafast optical nonlinearity in franckeite nanosheets has been further validated via an Er3+-doped fiber laser to deliver stable femtosecond pulse. The experimental results reveal that franckeite heterostructure nanosheets can be an ideal candidate in the design and manufacture of ultrafast nonlinear optoelectronic devices.