Figure 5. Characteristic energy values extracted from the spectra.

(a) The cutoff energies of the plateau and (b) the energies of the low-energy peak maxima extracted from the experimental and simulated energy spectra are plotted as a function of laser intensity. Simulation 1 and 2 are results from the re-scattering model and the transient thermionic emission model, respectively. The peak intensities for experiments and Simulation 1 are shown in the horizontal axis at the bottom, and the intensities for Simulation 2 are indicated at the upper side. The green dashed line indicates 10U_p expected from the classical cutoff law for ponderomotive energy gain. An example for the cutoff energy of the plateau is indicated by the arrow in Fig. 1(b). Error bars are added whenever the errors are bigger than the symbols.