Prof. Fritzsche also serves as Principal Editor for Computer Physics Communications, a peer-reviewed international journal with focus on the numerical analysis and software design in physics and physical chemistry. With the advent of new and tunable light sources, the electron dynamics of atoms and ions can nowadays be studied in great detail, from the femtosecond down to the attosecond scale. For instance, the irradiation of matter with intense FEL pulses hereby results in a large number of induced ionization, auto-ionization and recombination processes. To explore these - explicitly time-dependent - processes, we apply the density matrix theory to the emission and capture of electrons, and which combines analytical model with often extensive computations in order to achieve a quantitative (and predictive) understanding of light-matter interactions in strong fields. Beside of such atomic processes, we also investigate twisted particle beams carrying quantized angular momentum and the properties of highly-charged ions for their application in astro, nuclear and plasma physics.