1：Experimental Design and Method Selection:

The graphene-CuO nanocomposites were synthesized by the solvothermal method. The morphologies and structures of samples were investigated by x-ray diffraction, scanning electron microscopy, Raman spectroscopy and ultraviolet-visible absorption spectroscopy. The nonlinear optical (NLO) properties were tested by the Z-scan technology with 1030 nm laser pulses (340 fs, 1000 Hz).

2：Sample Selection and Data Sources:

Graphene-CuO nanocomposites with different mass ratios (1:

3：5 and

1) and pure graphene were prepared for comparison.

4：List of Experimental Equipment and Materials:

X-ray diffractometer (XRD, XPert MPD PRO, Cu Kα radiation), field-emission scanning electron microscope (SEM, Nova-400 NanoSEM), Raman spectrometer (Renishaw, RM-1000, 633 nm He-Ne laser), spectrophotometer (UV-2600), Z-scan system with femtosecond laser pulse (wavelength 1030 nm).

5：Experimental Procedures and Operational Workflow:

The samples were dispersed in ethanol and tested in the quartz cuvette (1 mm-thick) at room temperature.

6：Data Analysis Methods:

The nonlinear absorption coefficient (β) and nonlinear refractive index (γ) were calculated from the Z-scan data.