Fig. 5.

Cutoff comparison at different driving wavelengths from unexcited ZnO. a Measured spectra at different wavelengths. The intensities are slightly lower than Fig. 4 to observe the cutoffs. Spectra beyond 7 eV is not detected due to instrumental limitations. The cutoff from 1.8 µm appears not shorter than the cutoffs from long wavelengths at 2.3 and 3.6 µm. b The calculated cutoff appears not sensitive to the driving wavelength, in contrast to the well-known atomic case