Fig. 1. The first Brillouin zone in graphene.

Fig. 2. Comparison of our calculated conduction band population ρ_cc(k,t) in the velocity gauge (right column) with those from the two-band model (left column) given in Ref. [58] for panels (a) and (b) F₀ = 0.8 V/Å and panels (c) and (d) F₀ = 2.25 V/Å.

Fig. 3. The same as Fig. 2, but for panels (a) and (b) t = 0.75 fs and panels (c) and (d) t = 2.25 fs with the same F₀ = 1.0 V/Å.

Fig. 4. Comparison of the temporal evolution of the normalized single-electron current calculated by our method and those from TDDE for (a) p_y = 0, (b) p_y = 0.02A₀, and (c) p_y = 0.05A₀. In all the cases p_x/eA₀ = −0.75. In Fig. 4(a) we also show the result with Houston basis.

Fig. 5. Left column: the vector potential of laser pulse and electron current; Right column: the time evolution of the wave packet (red and black lines are classical trajectories).

Fig. 6. Comparison of harmonic spectra of graphene generated by laser fields with different ellipticity.

Fig. 7. The dependence of intensity in two perpendicular directions (x and y) of harmonics 3rd, 5th, 7th, and 9th on the ellipticity of driving laser pulse.

Fig. 8. (a) Harmonic radiation with different rotation angle θ. (b) The interband polarization d_cv (k) as a function of the crystal momentum k. (c) and (d) Harmonic spectra generated from inter-band polarization and intra-band current for θ of 0° and 20°, respectively.