Above threshold ionization beyond the high harmonic cutoff

Abstract

We present high sensitivity electron energy spectra for xenon in a strong 50 ps, 1.053 \ensuremath{\mu}m laser field. The above threshold ionization distribution is smoothly decreasing over the entire kinetic energy range (0--30 eV), with no abrupt changes in the slope. This is in direct contrast to the sharp cutoff observed in xenon optical harmonic generation spectra. Calculations using the single active electron approximation show excellent agreement with the observed electron distributions. These results directly address the unresolved relationship between the electron and photon emission from an atom in an intense field.