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A few-level simulation of the time-dependent dynamics of singly excited resonances of molecular hydrogen under the influence of moderately strong, ultrashort laser pulses

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Fan,  Daniel
Division Prof. Dr. Thomas Pfeifer, MPI for Nuclear Physics, Max Planck Society;

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Citation

Fan, D. (2020). A few-level simulation of the time-dependent dynamics of singly excited resonances of molecular hydrogen under the influence of moderately strong, ultrashort laser pulses. Bachelor Thesis, Ruprecht-Karls-Universität, Heidelberg.


Cite as: http://hdl.handle.net/21.11116/0000-0007-3657-B
Abstract
In this thesis a theoretical study of singly excited resonances of molecular hydrogen under the influence of moderately strong, ultrashort laser pulses was conducted. Motivated by a recent measurement of an absorption spectrum of H2, a deeper investigation of this system was needed. All numerical calculations were performed within the framework of a few-level model including interactions with laser fields. Certain parameters, as well as the investigated vibronic states in the model system, are obtained from experimental data, so that the system can qualitatively reproduce the real hydrogen. Resonant line shapes were examined. An XUV field is used as an excitation pulse, while an NIR pulse is used to couple dark states with bright states. In absence of an NIR field, the expected Lorentzian line shape could be observed. The full width at half maximum is determined geometrically and its relation to the lifetime is demonstrated successfully. In the presence of the NIR field, the line form becomes asymmetrical - a fit was performed for the occuring Fano line shape. The main goal was to observe time-resolved absorption spectra. The absorption spectra showed rich dynamics. To conclude how the time-dependent structures come about, a systematic investigation is performed by forbidding couplings between certain dark and bright states. This break-down of the system to simpler ones enabled us to deduce which couplings between the considered vibronic states cause which time changing structures, imprinted by electronic and nuclear degrees of freedom, in the spectrum.