High harmonics from backscattering of delocalized electrons

TL;DR

This paper demonstrates that electron backscattering can significantly enhance high-harmonic generation in finite periodic systems, with a maximum yield when the electron quiver amplitude matches the system size, supported by quantum and semiclassical models.

Contribution

It introduces a quantum and semiclassical analysis of high-harmonic generation due to electron backscattering in finite systems, revealing a maximum harmonic yield related to system size and electron dynamics.

Findings

Harmonic cutoff depends on electron backscattering at system edges.

Maximum harmonic yield occurs when twice the quiver amplitude equals the chain length.

The semiclassical model with finite electron-hole separation explains quantum results.

Abstract

It is shown that electron backscattering can enhance high-harmonic generation in periodic systems with broken translational symmetry. Paradigmatically, we derive for a finite chain of atoms the harmonic cutoff due to electrons backscattered from the edges of the chain and demonstrate a maximum in the harmonic yield if twice the quiver amplitude of the driven electrons equals the chain length. For an intuitive understanding of our quantum results we develop a refined semiclassical trajectory model with finite electron-hole separation after tunneling. We demonstrate that the same "tunnel exit" also holds for interband harmonics in conventional periodic solid-state systems.