High-harmonic generation in GaAs beyond the perturbative regime

The field-intensity dependence of high-harmonic generation in bulk gallium arsenide is studied. We experimentally find the oscillatory behavior at high fields where a perturbative scaling law no longer holds. By constructing a theoretical framework based on the Luttinger-Kohn model, we succeed in reproducing the observed oscillatory behavior. The qualitative agreement between the experiment and theory indicates that field-induced dynamic band modification is crucial in the nonperturbative regime. We show that the oscillatory behavior is naturally understood by dynamic localization that is based on the the Floquet subband picture.