| Summary: | The central topic of this thesis is the application of the R-matrix with time dependence (RMT) approach to describe the interaction of intense ultra-short laser pulses with general multi-electron atomic systems (specifically helium and carbon). The physical phenomena investigated in this thesis include above-threshold ionization, multiphoton ionization and inner-shell ionization. The RMT codes were first employed to investigate angular distributions of photoelectrons in two-colour two-photon above threshold ionization of helium as a testing ground for the codes. The calculated angular anisotropy parameters are compared with experimental findings. Subsequently the RMT codes were extended to treat open shell systems with non-zero initial magnetic quantum number, and these codes were used to investigate ejected electron momentum distributions in multiphoton ionization of carbon. Emphasis was put on how these distributions change for different magnetic quantum numbers. The RMT results were found to describe changes in magnetic quantum number due to the spin-orbit interaction in excellent agreement with pump-probe experiment. Finally, the RMT codes were used to study the competition between inner- and outer-shell ionization of carbon atoms by intense radiation in the soft x-ray energy range. This is a cutting-edge topic in view of possible experiments at free-electron laser facilities. In conclusion, the results outlined in this thesis present the R-matrix with time dependence theory as an accurate and efficient method to describe the interaction of ultrashort laser fields not only with noble gases, but also with open-shell systems. The ability of the RMT method to model a wide variety of atomic systems in these fields makes the approach an excellent choice for future comparison with experiment and a powerful tool in developing understanding of attosecond physics.
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