Electron energy spectra from the strong-field double-ionization of xenon

The electron energy spectra correlated to the strong-field double-ionization of xenon are presented at three laser intensities. The double-ionization electrons are on average more energetic than those generated from single-ionization. This difference in energy is not manifested as a simple scaling to higher electron energies, but rather as a change in the shape of the spectra. This trend is observed at all intensities. Most notably, the comparison between single- and double-ionization spectra is very similar at low and high peak, laser intensities. This could imply that a sequential double-ionization process dominates at all intensities, even where the double ion yield is enhanced.