A unified perspective of high-harmonic generation in gases and solids

TL;DR

This paper introduces a quantum optical model unifying high-harmonic generation mechanisms in gases and solids, revealing the dominance of intraband processes at low orders and a wavelength-independent switchover point.

Contribution

It provides a generalized quantum optical framework that captures both inter- and intraband HHG channels in gases and solids, improving quantitative accuracy.

Findings

Intraband HHG dominates at low harmonic orders.

The switchover harmonic energy is independent of pump wavelength.

The model predicts a faster harmonic power roll-off.

Abstract

We present a quantum optical generalization of the quantum-matter Lewenstein model of high-harmonic generation (HHG) in gases that contains two channels corresponding to the inter- and intraband HHG in solids. Both channels can be presented as a semiclassical current multiplied by the vacuum field strength, resulting in a quantitative correction and a faster roll-off of the harmonic power with order than in previous theories. In gases, like in solids, intraband HHG dominates at low orders; the switchover harmonic corresponds to a specific photon energy, independent of pump wavelength.