Routes to multiphoton double ionization in combined extreme ultraviolet and infrared laser pulses

Xenon multiphoton double ionization pathways are studied in a reaction microscope using a pump-probe arrangement of extreme ultraviolet high harmonic and infrared laser radiation. The momentum of photoelectrons is recorded in coincidence with singly or doubly charged ions. Among all possible routes to multiphoton double ionization, sequential processes using ionic excited states as intermediate steps are clearly identified.