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Abstract

The reconstruction of the full temporal dipole response of a strongly driven time-dependent system from
a single absorption spectrum is demonstrated, only requiring that a sufficiently short pulse is employed to
initialize the coherent excitation of the system. We apply this finding to the time-domain observation of
Rabi cycling between doubly excited atomic states in the few-femtosecond regime. This allows us to
pinpoint the breakdown of few-level quantum dynamics at the critical laser intensity near 2 TW=cm2 in
doubly excited helium. The present approach unlocks single-shot real-time-resolved signal reconstruction
across timescales down to attoseconds for nonequilibrium states of matter. In contrast to conventional
pump-probe schemes, there is no need for scanning time delays in order to access real-time information.
The potential future applications of this technique range from testing fundamental quantum dynamics in
strong fields to measuring and controlling ultrafast chemical and biological reaction processes when
applied to traditional transient-absorption spectroscopy.