B-spline ADC multi-electron theory for dynamical electronic systems in strong laser fields

Abstract

The work contained in this thesis focuses on the application of the ab initio numerical method based on algebraic diagrammatic construction theory to describe the correlated ionisation dynamics of many-electron systems in the presence of external laser fields. We utilise the B-spline basis set as it is capable of describing oscillating orbitals in the continuum very accurately. Two methods for calculating photo-electron spectra are introduced: the wave-function splitting and the time dependent surface flux method. The first part compares the photo-electron spectrum obtained with these two methods. The relevant variables for each method are then optimised, to ensure that artificial reflection off the grid boundary of the ionised wave-packet is kept to a minimum and that the numerical noise introduced by the method is reduced as much as possible. The second part of the thesis explores the multi-photon effect of above threshold ionisation (ATI). The photo-electron spectra for a variety of closed-shell atoms are calculated for infra-red fields of varying intensities, and the obtained angle-resolved and angle-integrated spectra are analysed. Important features, such as resonances and plateaus, are identified and discussed. The numerical method is applied to the carbon dioxide molecule and the impact of both Coulomb and dipole-induced inter-channel couplings on the calculated photo-electron spectra is discussed. The dependence of the ATI photo-electron spectrum of a neutral helium atom in the excited 2p state on the polarisation of the incident radiation is determined and the numerical results are compared to the predictions of an extended strong-field approximation theory. The final part examines the multi-electron Auger effect and introduces various approaches for the time-resolved study of the Auger decay process, including the streaking method and the attosecond pump-attosecond probe scheme. These schemes are simulated on the krypton atom with an Auger-active hole in the 3d orbital.