Behavior of the photoelectron boundary layer with sinusoidal time dependence

At high-incident photon intensities (X-rays, UV, or visible), a photoelectron boundary layer can form. This layer´s properties, and especially its electric dipole moment, change in a nonlinear way as the light intensity varies in time. We show here that the dipole moment obeys an exact dynamical equation, which can be used as the basis for analytic approximation schemes for a driver of arbitrary time dependence. An approximate analytic solution for a sinusoidally oscillating light source is presented, and compared with a particle-pusher numerical simulation. Scaling laws are extracted from the analytic solution