High-order harmonic generation from 2D periodic potentials in circularly and bichromatic circularly polarized laser fields

TL;DR

This study demonstrates the generation of high-order harmonics in 2D solids using circularly polarized laser fields, revealing controllable polarization and energy properties useful for solid imaging.

Contribution

It introduces a numerical simulation approach for HHG in 2D materials driven by circular and bicircular laser fields, highlighting novel polarization and tunability features.

Findings

Circular HHG occurs below the bandgap via intraband transitions.

Harmonics above the bandgap are elliptically polarized due to interband transitions.

Harmonic properties can be tuned by adjusting the phase difference in bicircular lasers.

Abstract

We studied the high-order harmonic generation (HHG) from 2D solid materials in circularly and bichromatic circularly polarized laser fields numerically by simulating the dynamics of single-active-electron processes in 2D periodic potentials. Contrary to the absence of HHG in the atomic case, circular HHGs below the bandgap with different helicities are produced from intraband transitions in solids with $C_4$ symmetry driven by circularly polarized lasers. Harmonics above the bandgap are elliptically polarized due to the interband transitions. High-order elliptically polarized harmonics can be generated efficiently by both co-rotating and counter-rotating bicircular mid-infrared lasers. The cutoff energy, ellipticity, phase, and intensity of the harmonics can be tuned by the control of the relative phase difference between the 1$\omega$ and 2$\omega$ fields in bicircularly polarized lasers, which can be utilized to image the structure of solids.