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Macroscopic Signatures of the Non-Perturbative Response of Single Layer Graphene to Intense Laser Fields

The development of ultrafast laser pulses is enabling unprecedented studies of the electronic dynamics of Dirac-Weyl materials subjected to intense fields. In particular, the generation of high-order harmonics in solid systems is emerging as a robust process to unveil such ultrafast dynamics through harmonic spectroscopy. In the general case, high-harmonic generation (HHG) in solids is performed in finite-gap systems [1] , [2] , in which electrons are promoted from the valence band to the conduction band through tunnel excitation, the counterpart to tunnel ionization in gases. However, gapless solids—such as graphene–have been also demonstrated to generate high-order harmonics following the non-adiabatic electron-hole excitation near the Dirac points [3] . Interestingly, this alteration of the first step leads to a different phenomenology in the HHG process. Up to now, most of the theoretical studies in single-layer graphene are restricted to the microscopic point of view [4] , where the spatial driving beam profile is neglected. However, the drivers’ intensity and phase distribution along the target is demonstrated a main source of phase matching phenomena, therefore the coherent macroscopic addition of the high harmonic radiation emitted at different regions of the target, is fundamental to reproduce experiments.