First-principles calculations for multiphoton absorption in α-quartz under intense short laser irradiation

We present a first-principles description for the electron dynamics and multiphoton absorption in crystalline SiO(2) induced by an optical field. We rely upon time-dependent density-functional theory with adiabatic local-density approximation, and a real-space and real-time method is employed to solve the time-dependent Kohn-Sham equation. Computational results show the absorption of photons to be in excess of the minimum required for electron excitation from the valence band to the conduction band. This is similar to the above threshold ionization in atoms and molecules.