Photoionization and photocurrents at sub-field-cycle temporal scale

The Keldysh theory of photoionization in solids is generalized to the case of arbitrarily short driving pulses of arbitrary shape and polarization. We derive a closed-form solution for the nonadiabatic ionization rate and field-driven currents in the solid-state electron-hole plasma. Our results indicate important role of ultrafast photoionization dynamics within the field cycle and link the ultrafast photoionization dynamics with experimentaly accessible quantities.