Mechanisms of high harmonic generation in solids

TL;DR

This paper clarifies the mechanisms behind high harmonic generation in solids, distinguishing between resonant and non-resonant processes, and highlights the dominant roles of interband currents and virtual processes depending on the driving laser wavelength.

Contribution

It introduces a theoretical formalism that separates resonant from non-resonant contributions in HHG and reveals the dominant mechanisms in different regimes, challenging existing one-electron-hole models.

Findings

Mid-infrared HHG is dominated by resonant interband currents.

Near-infrared HHG involves significant virtual processes due to Stark shifts.

Limitations of one-electron-hole theories are identified.

Abstract

The long standing issue of separating resonant from non-resonant processes in extreme nonlinear optics is resolved. The theoretical formalism is applied to high harmonic generation (HHG) in solids and reveals a deeper view into the dominant laser and material dependent mechanisms. Mid-infrared driven HHG in semiconductors is dominated by the resonant interband current. As a result of the dynamic Stark shift, virtual processes gain in importance in near-infrared driven HHG in dielectrics. Finally, our analysis identifies limitations of microscopic one-electron-hole theories.