EGAS41 - Swansea University

41 st EGAS PR 1 Gdańsk 2009
Molecules in intense ultrashort laser pulses
Alejandro Saenz
AG Moderne Optik, Institut für Physik, Humboldt-Universität zu Berlin, Hausvogteiplatz 5-7,
D-10117 Berlin, Germany
E-mail: Alejandro.Saenz@physik.hu-berlin.de
Recent laser technology allows to generate laser pulses in the infrared with a duration
of a few femtoseconds. This paves the route to probe ultrafast processes in, e.g., atoms
or molecules. This talk discusses two alternative approaches: one deals with real-time
observation of nuclear motion, the other concerns the time-resolved imaging of changes
in the electronic structure of molecules.
First, it is demonstrated how an ionizing ultrashort laser pulse can induce a vibrational
wavepacket not only in the formed ion, but also in the non-ionized neutral molecule. This
phenomenon, dabbed Lochfraß, is of purely quantum-mechanical origin and lead after its
theoretical prediction [1] to the so far fastest nuclear motion that could be experimentally
observed in real time [2]. In fact, the wavepacket induced in the case of a homonuclear
molecule like H 2 is shown to be extremely stable and behaves like a quantum pendulum or
molecular clock. Interestingly, it was recently claimed that starting from a more incoherent
initial state can lead to even more coherence induced by Lochfraß [3]!
In the second part of the presentation the possibility to image orbital structures in a
time-resolved fashion is discussed. For this purpose, the relation between the orientational
dependence of strong-field ionization and the shape of the highest-occupied molecular
orbital is demonstrated, but also possible problems are indicated. The consequences for
the possibility of watching chemical reactions in real time will be addressed.
References
[1] E. Goll, G. Wunner, A. Saenz, Phys. Rev. Lett. 97, 103003 (2006)
[2] Th. Ergler et al., Phys. Rev. Lett. 97, 103004 (2006)
[3] L. Fang, G.N. Gibson, Phys. Rev. Lett. 100, 103003 (2008)
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