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要旨:
In this work fundamental nonlinear dynamics inside the neon atom are studied
in two respects: At first, correlations between electronic inner-shell excitations in the
extreme-ultraviolet (XUV) spectral range are probed on their natural sub-femtosecond
time scale. To this end, the concept of attosecond transient absorption with a highharmonic
generated (HHG) attosecond and a single time-delayed moderately strong nearinfrared
(NIR) pulse was extended by a third, perturbative NIR pulse to perform timeresolved
four-wave-mixing spectroscopy. This allowed to retrieve coupling dynamics between
states of odd and even parity in a two-dimensional spectral representation. While
the first part of this work explores the sequential interaction of several weak and moderately
strong, fully coherent laser pulses with the target neon, the second part addresses
the impact of strong, partially-coherent fields delivered by the XUV free-electron laser in
Hamburg (FLASH). For this purpose, a novel beamline setup was developed and assembled
at FLASH which allowed to perform first XUV-pump—XUV-probe transient absorption
measurements. The measurements revealed the time-delay and intensity-dependent
control of sequential ionization processes, coherence-enhancement effects, and strongcoupling
signatures of bound—bound transitions in doubly-ionized neon. For the interpretation
of the experimental results numerical simulations based on quantum mechanical
few-level models were employed. Future applications of this method involve the
two-dimensional spectroscopy both with HHG and FLASH pulses to probe site-specific
information of electronic processes in molecules.
