  We propose a new technique to fully characterize the temporal structure of
extreme ultraviolet pulses by ionizing a bound coherent electronic wavepacket.
The populated energy levels make it possible to interfere different spectral
components leading to quantum beats in the photoelectron spectrum as a function
of the delay between ionization and initiation of the wavepacket. The influence
of the dipole phase, which is the main obstacle for state-of-the-art pulse
characterization schemes, can be eliminated by angle integration of the
photoelectron spectrum. We show that particularly atomic Rydberg wavepackets
are ideal and that wavepackets involving multiple electronic states provide
redundant information which can be used to cross-check the consistency of the
phase reconstruction.
