Electron-Backscattering-Assisted High Harmonic Generation from Bilayer Nanostructures

TL;DR

This study demonstrates that bilayer nanostructures can generate high-order harmonics with extended cutoffs through electron backscattering, offering a new method for high-energy light sources with tunable properties.

Contribution

It introduces a novel mechanism of high harmonic generation in bilayer nanostructures driven by electron backscattering, with detailed theoretical analysis and scaling laws.

Findings

Double-plateau harmonic spectra observed at grazing incidence.

Second plateau cutoff extends with increasing interlayer spacing d.

Harmonic yield is enhanced by longer driving laser wavelengths.

Abstract

In the framework of time-dependent density functional theory, we obtain high-order harmonics of photon energies up to 10 Up from bilayer crystals with an interlayer spacing d = 70 {\AA}. At grazing incidence, a clear double-plateau structure is observed in the harmonic spectrum. The photon energy of the second plateau far beyond atomic-like harmonics can be well explained by the inclusion of backscattering of ionized electrons. Ab initio simulations reveal that the cutoff of the second plateau is continuously extended with an increasing d. Our classical calculations predict that the maximum electronic kinetic energy is linearly dependent on d over a wide range. Moreover, the harmonic yield in the second plateau is significantly enhanced by increases in the wavelength of the driving laser. Owing to the confined spreading of the electronic wave packet, a beneficial wavelength scaling of {\lambda}2.85 is obtained. This study therefore establishes a novel and efficient way of producing high-energy light source based on layered nanostructures.