Figure 2
Experimental and simulated energy spectra together with extracted characteristic intensities.
(a) Experimental and (b,c) simulated energy spectra for different laser peak intensities. Simulation 1 and 2 are simulated based on the re-scattering model and the transient thermionic emission model, respectively. Corresponding laser fields in the simulations represent the maximum laser fields at the focus without field enhancement. The enhancement factor is 2.4 in our case3,4. The applied DC voltage has been subtracted from the energy scale such that 0 eV corresponds to the Fermi energy CF of the tip. (d) Evolution of the peak and plateau intensities in the experimental energy spectra for two different DC voltages (open circles), plotted as a function of laser peak intensity including the field enhancement by a factor of 2.4 at the tip apex. Filled triangles in the left panel show peak intensities from an earlier study in the weak-field regime3,4; their count rates are indicated in the vertical axis at the right side. The scale is adjusted in such a way the level of the data points of the two diffierent experiments become the same around 2 × 1012 W/cm2. The error bars in peak intensities are due to uncertainty in the beam waist at the focus. (e,f) Same for the simulated energy spectra. The dashed lines in (d–f) indicate lines with a slope of 2.
