Excitation of electrons in a silicon crystal under irradiation by ultrashort laser pulses has been modeled numerically in collaboration with Max Planck Institute for the Structure and Dynamics of Matter (MPSD), Hamburg, Germany.
The simulations were performed based on the time-dependent density functional theory (TDDFT), taking into account the realistic band structure of the crystal as well as the temporal shape of the laser pulse. The simulation data were compared with the well-established theories such as the Keldysh model of electron excitation and the Drude model of energy absorption. The results provide key insights into the electron excitation dynamics as a function of irradiation parameters (laser intensity, wavelength, pulse duration). Multiphoton excitation rates have been calculated for the laser irradiation regimes beyond the validity ranges of the established theories.
Energy absorbed by electrons as a function of photon energy for the laser field amplitudes of E = 0.5, 0.75, 1.0, 1.5, 2, 3, 4, 5 V/nm (curves from bottom to top) obtained in the TDDFT simulations (solid lines), and using a macroscopic Drude model (dashed lines). The energy is given per one atom of silicon crystal. The calculations were performed for a top-hat temporal shape of laser pulses with duration of 20 fs.