U$\text{}_{P}$, 3U$\text{}_{P}$, 11U$\text{}_{P}$: Above-Threshold Ionization Revisited

Angular distributions of very high energy photoelectrons from Xe and Kr, excited by a 50 ps, 1054 um laser, are presented. In Xe strong, narrow structures 45° off the polarization axis appear on above-threshold ionization peaks within a limited energy range centered around 9U$\text{}_{P}$, where U$\text{}_{P}$ is the intensity-dependent ponderomotive energy. Under the same conditions the effect is much weaker in krypton. These structures are discussed using a very simple classical model as well as sophisticated single active electron calculations and the Keldysh-Faisal-Reiss theory. We conclude these structures are the result of single-electron dynamics involving rescattering of a tunneling component of the continuum wave function.