Resonance-enhanced solid high-order harmonic generation by a chirped laser pulse

The resonant high-order harmonic generation (HHG) from solid in the periodic potential is investigated by a chirped laser pulse. We show the dependence of the intensity of the resonance peak on the chirp parameters beta, and it is found that the increase of the resonant harmonic intensity with beta is significantly higher than that of the nonresonance ones. The frequency of the resonance peaks remains at 4.2 eV, which equals to the band gap energy between the valance band (VB) and the conduction band (CB1). By adjusting the chirp parameters, the electron will be injected into the conduction band which results in the band gap emission. Through the time-dependent population imaging (TDPI) and the time-frequency (TF) investigation, we demonstrate that the resonance peak originates from the transition of electrons from the VB toward CB1.