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要旨:
In this work the importance of phases in time-resolved spectroscopy
is investigated in two respects. At first, the influence of the phase of a system’s dipole
response after excitation is studied. Previous transient-absorption experiments in helium
allowed the measurement and control of this phase of an emitting dipole by a second, coupling
laser pulse. The derived concept is now generalized to a more complex system, i.e. a
dye molecule in the liquid phase. For this purpose, a setup for transient-absorption measurements
with femtosecond infrared laser pulses is developed and assembled and numerical
simulations support the interpretation of the experimental results. It was found that
only specific excited states couple strongly to the laser field. While the foregoing experiments
rely on the full coherence of laser pulses, the second part of this work addresses the
impact of partially coherent phases of laser pulses. Pump–probe experiments in gaseous
deuterium molecules applied statistically fluctuating pulses delivered by a Free-Electron
Laser source. These measurements revealed an enhanced temporal resolution on time
scales shorter than the average pulse duration. For the description and explanation of the
observations a novel approach is developed which is based on the correlation of temporally
random substructures of the pulses. In order to realize noisy pulses in the laboratory,
a pulse shaper is designed and built up which is capable to modify the spectral phase of the
laser pulses. Thereby, this developed general method is transferred to transient-absorption
measurements in the liquid phase and its universal applicability is demonstrated.
