Intra- and Interband Transitions in High-Order Harmonic Generation from Solids

We introduced a quasi-classical step-by-step model for interband transitions in the k space to reveal the mechanisms of high-order harmonic generation (HHG) in solids. The ultrafast dynamics are also investigated in the real space by solving the time-dependent Schrodinger equations. The inter- and intraband dynamics in k space correspond to the local and global oscillations of the Bloch electron wave packet in the coordinate space moving at phase and group velocities, respectively. Their contributions can be controlled by different laser parameters, such as chirp, pulse duration, carrier-envelope phase, two-color field, and so on. We also introduced an efficient way to enhance the yield of HHG in inhomogeneous laser fields below the damage threshold.