Applications of time-dependent configuration-interaction singles for photoelectrons in attosecond and free-electron laser sciences

Sammanfattning: This thesis addresses the theoretical treatment of photoelectrons in attosecond and free-electron laser sciences. Wehave implemented methods that extract information on the photoionization process, which we use to investigateinterferometric schemes with particular focus on multiphoton ionization and strong-field effects in attosecondmetrology and coherent control of photoelectrons in free-electron laser science.This thesis comprises six papers.In Paper I, we investigate photoelectron angular distributions in laser-assisted photoionization. We confirmearlier predictions of a propensity rule for continuum transitions and discuss interference effects.In Paper II, we interpret experiments from attosecond and free-electron laser sciences in terms of an interactionphase and devise a rule of thumb for predicting general phase and amplitude effects in these experiments.In Paper III, we experimentally determine the one-photon dynamics for each angular momentum channel, as afunction of energy, by studying two-photon photoelectron angular distributions.In Paper Iv, we experimentally and theoretically investigate periodic population transfer between two boundstates in helium at XUV wavelengths by studying the photoelectron spectra.In Paper v, we present a general implementation of time-dependent configuration interaction for atomic sys-tems.In Paper vI, we discuss size-consistency problems in velocity gauge in truncated configuration spaces and pro-pose a correction based on the Thomas–Reiche–Kuhn sum rule. We further predict the occurrence of dynamicalinterference in laser-assisted photoionization.