Enhanced high-order harmonic generation from periodic potentials with initial superposition states

We theoretically investigate the high-order-harmonic generation (HHG) from solids in periodic potentials. The harmonic spectrum is simulated by solving the time-dependent Schödinger equation in a monochromatic laser field. The numerical results show that the intensity of the high-order harmonics from the superposition of the conduction band minimum (CBM) and valence band maximum (VBM) states is about three orders of magnitude higher than that from the VBM alone in the plateau region. Our results show that conduction band population in the initial state affects the intensity of HHG. The physical mechanism is discussed by the picture of time-dependent population imaging (TDPI)