Single- and multiple-electron dynamics in the strong-field tunneling limit

Evolution of atomic ionization into the strong-field limit offers the opportunity to study the fundamentals of atom-laser interaction. In this study, we report on high precision measurements of the ion and electron distributions from laser-excited helium and neon atoms which reflect the changing continuum dynamics as the ionization process evolves into the pure tunneling regime. The experiments present evidence of both single- and two-electron ionization. These data provide a direct quantitative test of various theories of strong-field ionization. We show that a relatively simple semiclassical model which includes a description of a field-driven electron elastically rescattering from an accurate ion core potential reproduces the measured electron distributions for both atoms. However, using this model to calculate e-2e inelastic rescattering yields cross sections which are incompatible with the measured two-electron ionization.