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Zeitaufgelöste Untersuchungen zur Fragmentationsdynamik von H2 (D2) in ultra-kurzen Laserpulsen


Ergler,  Thorsten
Division Prof. Dr. Joachim H. Ullrich, MPI for Nuclear Physics, Max Planck Society;

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Ergler, T. (2006). Zeitaufgelöste Untersuchungen zur Fragmentationsdynamik von H2 (D2) in ultra-kurzen Laserpulsen. PhD Thesis, Ruprecht-Karls Universität, Heidelberg.

In course of this work pump-probe experiments aimed to study ultrafast nuclear motion in H2 (D2) fragmentation by intense 6-25 fs laser pulses have been carried out. In order to perform time-resolved measurements, a Mach-Zehnder interferometer providing two identical synchronized laser pulses with the time-delay variable from 0 to 3000 fs with 300 as accuracy and long-term stability has been built. The laser pulses at the intensities of up to 1015 W/cm2 were focused onto a H2 (D2) molecular beam leading to the ionization or dissociation of the molecules, and the momenta of all charged reactions fragments were measured with a reaction microscope. With 6-7 fs pulses it was possible to probe the time evolution of the bound H+2 (D+2 ) nuclear wave packet created by the first (pump) laser pulse, fragmenting the molecule with the second (probe) pulse. A fast delocalization, or "collapse", and subsequent "revival" of the vibrational wave packet have been observed. In addition, the signatures of the ground state vibrational excitation in neutral D2 molecule have been found, and the dominance of a new, purely quantum mechanical wave packet preparation mechanism (the so-called "Lochfrass") has been proved. In the experiments with 25 fs pulses the theoretically predicted enhancement of the ionization probability for the dissociating H+2 molecular ion at large internuclear distances has been detected for the first time.