Fig. 1. (a) AFM image of the as-prepared GO nanosheets. (b) Solution-processed preparation of flexible GO–PVA sheets by impregnating GO into PVA matrix and its bright field imaging. The inset is the schematic representation of GO–PVA sheets.

Fig. 2. (a) UV–Vis–NIR transmittance spectra of GO–PVA sheets prepared with different GO/PVA weight ratios. (b) Raman spectra of GO before and after the impregnation into PVA sheet.

Fig. 3. Open aperture Z-scan results of a GO–PVA sheet (GO∶PVA=0.0025∶1) at (a) 400 and (b) 800 nm under different excitation fluences. Optical limiting response of GO–PVA sheets of different GO/PVA weight ratios under femtosecond laser pulses at (c) 400 and (d) 800 nm, respectively.

Fig. 4. Open aperture Z-scan results of a GO–PVA sheet (GO∶PVA=0.0025∶1) at 1400 nm under excitation fluence of 68  mJ/cm2. This sample was kept in the different moisture conditions for more than 24 h before test.

Fig. 5. Excitation fluence dependent ultrafast relaxation dynamics of GO–PVA sheet (GO∶PVA=0.0025∶1) measured by femtosecond pump–probe technique. Inset shows the normalized data on a shorter time scale.