  Autoionization, which results from the interference between direct
photoionization and photoexcitation to a discrete state decaying to the
continuum by configuration interaction, is a well known example of the
important role of electron correlation in light-matter interaction. Information
on this process can be obtained by studying the spectral, or equivalently,
temporal complex amplitude of the ionized electron wavepacket. Using an
energy-resolved interferometric technique, we measure the spectral amplitude
and phase of autoionized wavepackets emitted via the sp2+ and sp3+ resonances
in helium. These measurements allow us to reconstruct the corresponding
temporal profiles by Fourier transform. In addition, applying various
time-frequency representations, we observe the build up of the wavepackets in
the continuum, monitor the instantaneous frequencies emitted at any time and
disentangle the dynamics of the direct and resonant ionization channels.
