High-order harmonic generation of ZnO crystals in chirped and static electric fields

Abstract

High harmonic generation (HHG) in ZnO crystals under chirped single-color field and static electric field are investigated by solving the semiconductor Bloch equation (SBEs). It is found that when the chirp pulse is introduced, the interference structure become obvious while the harmonic cutoff is not extended. Furthermore, the harmonic efficiency is improved when the static electric field is included. These phenomena are demonstrated by the classical recollision model in real space affected by the waveform of laser field and inversion symmetry. Specifically, the electron motion in k-space shows that the change of waveform and the destruction of the symmetry of the laser field lead to the incomplete X-structure of the crystal-momentumresolved (k-resolved) inter-band harmonic spectrum. Furthermore, a pre-acceleration process in the solid four-step model is confirmed.