Adiabatic approach for high harmonic generation in solids induced by intense low-frequency pulses

An analytic description of high harmonic generation (HHG) in solids induced by intense low-frequency pulses is presented within an adiabatic approach, which treats laser-matter interactions nonperturbatively. We derive the analytical expression for the laser-dressed state of an electron in an arbitrary spatially periodic potential, taking into account multiband structure of the solid target. Closed-form formulas for electron current and HHG spectra are presented. Based on the developed theory, we provide an analytic explanation for key features of HHG yield and show that the interband mechanism of HHG prevails over the intraband one.