Enhanced high-order harmonic generation in semiconductors by excitation with multicolor pulses

Abstract

We investigate high-order harmonic generation (HHG) in ZnO driven by linearly polarized multicolor pulses. It is shown that the intensities of the harmonics in the plateau region can be enhanced by two to three orders of magnitude when driven by two- or three-color fields as compared with the single-color pulse excitation. By analyzing the time-dependent population in the conduction band as function of both the initial and the moving crystal momenta, we demonstrate that the intraband preacceleration of electrons from their initial momenta to the top of the valence band prior to ionization can occur when driven by linearly polarized multicolor pulses, which greatly influences the interband excitation and the subsequent HHG. Moreover, we show that short trajectories can be enhanced whereas long trajectories are suppressed by multicolor pulses. All these effects account for the observed remarkable enhancement of HHG. Our results confirm the very recently proposed four-step model for high-order harmonic generation in semiconductors and provide an effective way to enhance the intensities of harmonics in the plateau region, which has significant implications for the generation of bright attosecond light sources from semiconductors.