Frankfurt 2006 – scientific programme

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SYIF: Intense field interaction with molecules and clusters

SYIF 2: Intense field interaction with molecules and clusters 2

SYIF 2.1: Invited Talk

Friday, March 17, 2006, 16:30–17:00, HV

Applications of Attosecond Lasers to Atoms and Molecules in Strong Laser Fields — •Marc Vrakking — FOM Institute for Atomic and Molecular Physics, P.O. Box 41883, 1009 DB, Amsterdam, NL

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 attosecond laser techniques. Recently the production and characterization of attosecond pulses has become possible. 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. On the other hand, studies of photo-absorption in weak laser fields are extremely important, since all photo-absorption processes in nature (i.e. outside a laser laboratory) occur in this regime. In my talk I will discuss experiments aimed at observing the motion of electrons on attosecond timescales in strong laser fields in situations where we believe that this motion explains previously made observations. An interesting example is so-called dynamic molecular alignment. For a number of years we have known that exposure of molecules to intense (femtosecond) laser fields leads to alignment of the molecule along the laser polarization axis. The accepted explanation for this phenomenon is that the electric field of the laser creates an oscillatory electron motion that generates a dipole and - in combination with the laser electric field - a torque that forces the molecule into alignment. I will discuss experiments that show very direct evidence for the existence of this oscillating dipole.