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Zielinski, Alejandro (2016): Fully differential photo-electron spectra of hydrogen and helium atoms. Dissertation, LMU München: Fakultät für Physik



The ability to probe and manipulate electron dynamics and correlations on their characteristic time scales would open up many technological and scientific possibilities. While modern laser technology already allows to do that in principle, a lot of theoretical ground work is still missing. This thesis focuses on the elementary effect of laser strong field ionization of the two simplest systems: The Hydrogen and Helium atoms. To that end, the time-dependent Schroedinger equation is solved numerically, and photo-electron spectra are extracted using the highly efficient tSurff technique. We implemented both the one and two particle versions of tSurff together with several other numerical techniques in a new parallelizable C++ code. We provide details on the employed methods and algorithms, and study numerical efficiency properties of various approaches. We propose a description of the electric field interaction in a mixture of length and velocity gauge for the correct and most efficient implementation of a coupled channels approach, which can be used to compute accurate single ionization photo-electron spectra from true multi-electron systems, even molecules. We provide extensive numerical data for a detailed study of the Hydrogen atom in an Attoclock experimental setup, where it is found that the involved strong field tunnel ionization processes can be considered instantaneous. In particular, there appear no tunneling delays, which can be used as a calibration for experiments with more complicated targets. Similarly, it is investigated whether discrepancies between theory and experimental data for the longitudinal photo-electron momentum spread, resulting from photo-ionization of Helium in elliptically polarized laser pulses, can be explained by non-adiabatic effects, and a related consistency problem in current laser intensity calibration methods is pointed out. We further show that Fano resonance line shapes of doubly excited states in the Helium atom, prominently appearing in single ionization spectra generated by short wavelength laser pulses, can be controlled by an external long wavelength streaking field. The resulting line shapes are still characterized by the general Fano situation, but with a complex - rather than real - Fano parameter. We provide a theoretical description of this two color process and prove numerically that the entire doubly excited state series exhibits synchronized line shape modifications as the specifics of the involved states are unimportant. Finally, we compute fully differential double ionization spectra and suggest a measure of correlation that is directly applicable to experimental data. We confirm literature results at short wavelengths, and achieve to compute five-fold differential double ionization photo-electron spectra at infrared wavelengths from the Helium atom, thereby reproducing a characteristic several orders of magnitude enhancement of double emission due to correlation effects.