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Abstract:
Within this thesis, the dynamical response of small quantum systems
after the absorption of multiple extreme-ultraviolet (XUV) photons is studied via
two-color pump-probe experiments at the free-electron laser (FEL) in Hamburg
(FLASH) by employing many-particle recoil-ion momentum spectroscopy.
The multi-photon ionization of argon atoms is investigated at a photon energy of
27 eV and FEL intensities of 1013 - 1014W=cm2. The sequential ionization channel
is found to dominate and intermediate resonances are revealed by a delayed infrared
(IR) laser pulse.
Molecular hydrogen (H2) is studied at a photon energy of 28.2 eV. Dissociation via excited states and fragmentation by sequential two-photon ionization are observed.
In addition, it is shown how the ground-state dissociation of H+2
can be used as a
tool to determine the temporal overlap between an XUV and IR laser pulse.
In the argon dimer, multiple interatomic relaxation processes are triggered by the
absorption of several 27-eV-photons. Besides interatomic Coulombic decay (ICD),
frustrated triple ionization and charge transfer at crossings of potential energy curves
are observed. The lifetime of charge transfer is determined to be (531 +/- 136) fs using
an XUV-IR pump-probe scheme.
The employed reaction microscope is upgraded by an in-line XUV split-delay and focussing optics, which was designed and commissioned as part of this thesis.
