Images of photoelectrons formed in intense laser fields

Spatial distributions of photoelectrons produced by multiphoton ionization of xenon atoms are recorded by projecting the expanding photoelectron cloud onto a two-dimensional position sensitive detector. The projected image provides a direct view of the squared angular wave functions of the free electrons as well as their energy distribution. The results confirm recent observations that intermediate state resonances with 5f and 4f character establish the dominant ionization paths at low intensity, for short pulse excitation at 640 and 620 nm. At higher intensity more complex superpositions occur with formation of electrons with continuous distributions at low energies.