Interference from interband harmonics generated by different crystal momentum channels

We theoretically investigate the high-order harmonic generation (HHG) of zinc oxide (ZnO) induced by linearly polarized laser pulses. It is found that the harmonic spectrum exhibits fine subpeak structures, which is related to the interband polarization arising from electron-hole interactions. Further numerical analyses show that the subpeak structures originate from the interference between the interband harmonics, which are generated by different crystal momentum channels around the top of the valence band. Additionally, we extend our inquiry to solid HHG driven by a two-color laser field. Intriguingly, our findings indicate a notable suppression of harmonic subpeak structures in this context. To gain insight into the governing physical mechanisms, we illustrate the time-dependent population in the conduction band. Our analysis underscores a phenomenon of electron preacceleration before ionization. Consequently, the crystal momentum channels around the top of the valence band exhibit diminished contributions to HHG, leading to the effective suppression of harmonic subpeak structures. Our results may provide insights into the underlying mechanisms of solid HHG.