In the past two decades femtosecond time-resolved experiments have allowed
the observation of molecular rotations and vibrations, and of photo-induced
chemical processes. However, these experiments often tell only half the
story: they show the motion of atoms moving under the influence of
potential energy curves that result from a time-average over the motion of
all electrons in the system. The natural time-unit for this electronic
motion itself is the atomic unit of time (1 a.u. = 0.024 fsec = 24
attoseconds). Real-time observation of this motion therefore requires
recently developed attosecond laser techniques.
When considering motions of electrons we may distinguish between motion that results from driving the electrons with a strong laser field and motion that results from photo-absorption in a weak laser field. In strong laser fields the electron motion can be quite intuitive. Eventually, studies of photo-absorption in weak laser fields will be more important though, since all photo-absorption processes in nature (i.e. outside a laser laboratory) occur in this regime.
In my talk I will present a personal perspective on the current status of attosecond science, discussing a number of requirements for both further experimental and theoretical developments of the field. I will discuss how there is both a utility for isolated attosecond pulses and attosecond pulse trains, and will argue that interesting attosecond science already starts at the level of perturbative atom-light field interactions.
I will discuss ongoing experiments aimed at observing the motion of electrons on attosecond timescales in strong laser fields. An interesting example is the dissociative ionization of the hydrogen molecule (into a proton and a neutral atom), where we have recently observed that the dissociation process can be controlled by the carrier envelope phase of a few-cycle laser pulse. 
 M.F. Kling, Ch. Siedschlag, A.-J. Verhoef, J.I. Khan, M. Schultze, Th. Uphues, Y. Ni, M. Uiberacker, M. Drescher, F. Krausz and M.J.J. Vrakking, Science (in press, 2006).
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