Figure 5. Comparison of calculated graphene plasmon-assisted HHG and measured HHG from bulk semiconductors.

(a) We show the emission intensities of high harmonics normalized to the intensity of the fundamental peak as a function of pulse fluence. Each panel corresponds to the emission of the harmonic indicated in its lower-right corner, calculated with the MDF-CEM method either for a 100 nm-wide graphene nanoribbon doped to E_F=0.4 eV (solid squares) or for undoped (E_F=0, open hexagons) and doped (E_F=0.4 eV, solid diamonds) extended graphene. For comparison, we also plot theoretical (open symbols) and experimental (solid symbols) results for bulk GaSe taken from ref. 13 (triangles) and ref. 16 (circles). (b) Comparison of HHG transmission intensity (∝|E_t|²) normalized to the incident intensity (∝|E₀|²) for a doped-graphene ribbon array (100 nm width, 200 nm period, E_F=0.4 eV, solid squares) and undoped extended graphene (open hexagons), calculated with the MDF-CEM method at the peak harmonic frequencies. We consider 100 fs FWHM pulses centered at 0.158 eV (that is, the 100 nm ribbon plasmon) in all cases.