Theoretical Analysis of High-Harmonic Generation in Solids

TLDR

The study theoretically investigates high‑harmonic generation in bulk crystals driven by intense mid‑infrared lasers with photon energies below the band gap. The analysis focuses on the two main mechanisms of HHG—interband and intraband—in bulk crystals. The authors find that the previously neglected interband current dominates HHG, with saddle‑point analysis revealing an atomic‑like picture, and that interband and intraband mechanisms exhibit distinct wavelength dependencies that can be experimentally distinguished.

Abstract

We investigate theoretically high-harmonic generation (HHG) in bulk crystals exposed to intense midinfrared lasers with photon energies smaller than the band gap. The two main mechanisms, interband and intraband HHG, are explored. Our analysis indicates that the interband current neglected so far is the dominant mechanism for HHG. Saddle point analysis in the Keldysh limit yields an intuitive picture of interband HHG in solids similar to atomic HHG. Interband and intraband HHG exhibit a fundamentally different wavelength dependence. This signature can be used to experimentally distinguish between the two mechanisms in order to verify their importance.