Photoionization by an ultraintense laser field: Response of atomic xenon

Abstract

We present energy- and angle-resolved photoionization from Xe in an ultrastrong laser field at 10{sup 19} W/cm{sup 2}. The observed yields are consistent with the tunneling ionization of Xe{sup 9+} to Xe{sup 24+}. However, energy and angle-resolved photoelectron spectra show differences for electrons whose final energies are above or below 0.5 MeV, which is approximately the ponderomotive energy at these intensities. Above 0.5 MeV, the observed photoelectron cutoff energy (between 1 and 1.35 MeV), photoelectron energy spectra, and the angle-resolved photoelectron azimuthal distributions agree with a model using tunneling ionization, multiple charge states, a classical relativistic continuum, and nonparaxial three-dimensional (3D) focused laser field. Below 0.5 MeV the yields and angular distributions observed indicate dynamics not included within a classical, single electron model of the interaction.