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Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 05/05 Podcast
Fully differential photo-electron spectra of hydrogen and helium atoms

Fully differential photo-electron spectra of hydrogen and helium atoms

Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 05/05 vor 10 Jahren

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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.