Comparison of high-order harmonic generation in defect-free and defective solids with different time delays

We theoretically investigate the high-order harmonic generation (HHG) of defect-free solids by solving the time-dependent Schrödinger equation (TDSE). The results show that the harmonic intensity can be enhanced, harmonic order can be extended, and modulation near the cutoff order becomes smaller for the second plateau by increasing the time delay. These effects are due to an increase of the electron population in higher energy bands, where the larger band gap allows electrons to release more energy, and the long electronic paths are suppressed. Additionally, we also investigate the HHG of defective solids by Bohmian trajectories (BT). It is found that the harmonic intensity of the second plateau can be further enhanced. Simultaneously, cutoff order is also extended due to Bohmian particles moving farther away from the defective zone.