Elastic Rescattering in the Strong Field Tunneling Limit

High precision measurements of helium photoelectron energy and angular distributions for a broad intensity range reflect the change in the continuum dynamics that occurs as the ionization process evolves into the pure tunneling regime. Elastic rescattering of the laser-driven free electron from its parent ion core leaves a distinct signature on the spectra, providing a direct quantitative test of the various theories of strong field multiphoton ionization. We show that it takes a relatively complete semiclassical rescattering model to accurately reproduce the observed distributions.