Atomic and Molecular Dynamics Probed by Intense Extreme Ultraviolet Attosecond Pulses
Abstract: This thesis work was aimed to investigate dynamical processes in atoms and molecules on ultrafast time scales initiated by absorption of light in the extreme ultraviolet (XUV) regime. In particular, photoionization and photodissociation have been studied using pump-probe techniques involving ultrafast laser pulses. Such pulses are generated using either high-order harmonic generation (HHG) or free-electron lasers (FELs).The work of this thesis consists to a large extent in the development and application of a light source, enabling intense XUV attosecond pulses using HHG. In a long focusing geometry, a high-power infrared laser is frequency up-converted so as to generate a comb of high-order harmonics. An important aspect was the study of the spatial and temporal properties of the generated light pulses in order to gain control of their influence on the experiment. Combining theoretical and experimental results, the effect of the dipole phase on properties of high-order harmonics was explored, along with a metrological series of studies on the harmonic wavefront and the properties of the focusing optics used. Further, the HHG light source was employed to investigate photoionization. Individual angular momentum channels involved in the ionization were characterized using two-photon interferometry in combination with angle-resolved photoelectron detection. A method is applied allowing the full determination of channel-resolved amplitudes and phases of the matrix elements describing the single-photon ionization of neon.Finally, the process of photodissociation was investigated using light pulses generated via both HHG and FELs. The dissociation dynamics induced by multiple ionization of organic molecules were studied. Correlation techniques were used to unravel the underlying fragmentation dynamics, and additionally, pump-probe experiments provided insights into the time scales of the (pre-)dissociation dynamics.
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