  The dependency on the excitation energy of ultrafast multi-photon ionization
of xenon by intense, short extreme ultraviolet pulses (XUV) was investigated in
the vicinity of the 4$d$ 'giant' resonance using ion time-of-flight
spectroscopy. The yields of the high charge states of xenon show strong
variations with the excitation energy. With reference to simulated absorption
spectra, we can link the photon energy dependency to resonance structures of
single-electron excitations mainly in the xenon N-shell and purely sequential
multi-photon absorption.
