Atomic-like high-harmonic generation from two-dimensional materials

The generation of high-order harmonics from atomic and molecular gases enables the production of high-energy photons and ultra-short isolated pulses.
Here, we demonstrate from ab initio simulations that it is indeed possible to generate high-order harmonics from free-standing monolayer materials, with a similar energy cutoff than in atomic and molecular gases.
Electrons driven perpendicularly to the monolayer plane behave qualitatively the same as the electrons responsible for high-harmonic generation (HHG) in atoms, their trajectories being described by the widely used semi-classical model.
Spite of the similarities, the first step and the last step of the well-established three-step model for atomic HHG are remarkable different in the two-dimensional materials from gases.
We show that the electron-electron interaction plays an important role in harmonic generation from monolayer materials, due to strong local-field effects and that the recombination of the accelerated electron wavepacket is modified, due to the infinite extension of the monolayer.
Our results establish a novel and efficient way of generating high-order harmonics based on a solid-state device, with similar energy cutoff and more favorable wavelength scaling of the harmonic yield than in atomic and molecular gases.