Intensity-dependent scattering rings in high order above-threshold ionization

Angular distributions of high energy photoelectrons from Xe and Kr, excited by a 50 ps, 1.05 μm laser, are presented. In Xe, strong, narrow rings ∼45 ° off the polarization axis appear in a limited energy range centered around 9${\mathit{U}}_{\mathit{p}}$, where ${\mathit{U}}_{\mathit{p}}$ is the ponderomotive energy. This effect is much weaker in Kr. Single active electron calculations agree well with these observations. We conclude that the rings result from single-electron ionization dynamics, most likely involving rescattering from the ion core of the tunneling component of the continuum wave function.