arXiv2015
Recent developments toward the production and laboratory use of pulses of high intensity, and/or of very high frequency, and/or of ultrashort duration, make possible experiments which can produce time-resolved data on ultrafast transformations involving motions of electrons. The formulation, quantitative understanding and prediction of related new phenomena entail the possibility of computing and applying solutions of the many-electron time-dependent Schroedinger equation, for arbitrary electronic structures, including the dominant effects of Rydberg series, of multiply excited states and of the multi-channel continuous spectrum. To this purpose, we have proposed and applied to many prototypical cases the state-specific expansion approach (SSEA). (Mercouris, Komninos and Nicolaides, Adv. Quantum Chem. 60, 333 (2010)). The paper explains briefly the SSEA, and outlines four of its applications to recently formulated problems concerning time-resolved electronic processes, where electron correlations are crucial. These are, 1) The time resolution of the decay of polyelectronic unstable states, 2) The excitation and decay of strongly correlating doubly excited states and atto-time-resolution of their geometries, 3) The time-resolved process of formation of the interference profiles of resonance states during the femtosecond photoionization of Helium and Aluminum, and 4) The relative time delay in the (2s,2p) photoionization of Neon by an attosecond pulse.