Efficient high-harmonic generation in graphene with two-color laser field at orthogonal polarization

TL;DR

This paper demonstrates that orthogonal two-color laser fields significantly enhance high-harmonic generation in graphene, surpassing parallel polarization, due to unique interband transition dynamics and many-particle Coulomb interactions.

Contribution

It reveals the effectiveness of orthogonal polarization in high-harmonic generation in graphene and extends the semi-classical model to include many-particle Coulomb effects.

Findings

Orthogonal polarization yields over two orders of magnitude stronger harmonics than parallel polarization.

Many-particle Coulomb interactions further enhance the high-harmonic generation signal.

The extended model explains the physical origin of the polarization-dependent enhancement.

Abstract

High-order frequency mixing in graphene using a two-color radiation field consisting of the fundamental and the second harmonic fields of an ultrashort linearly polarized laser pulse is studied. It is shown that the harmonics originated from the interband transitions are efficiently generated in the case of the orthogonally polarized two-color field. In this case, the generated high-harmonics are stronger than those obtained in the parallel polarization case by more than two orders of magnitude. This is in sharp contrast with the atomic and semiconductor systems, where parallel polarization case is more preferable. The physical origin of this enhancement is also deduced from the three-step semi-classical electron-hole collision model, extended to graphene with pseudo-relativistic energy dispersion. In particular, we discuss the influence of the many particle Coulomb interaction on the HHG process within dynamical Hartree-Fock approximation. Our analysis shows that in all cases we have an overall enhancement of the HHG signal compared with the free-charged carrier model due to the electron-hole attractive interaction.