Angular distributions and time ordering in double ionization of helium: approaching the long-wavelength regime

Abstract

With the progress in laser technologies over recent years it has become possible to create coherent and intense extreme ultraviolet (XUV) pulses via high-harmonic generation with durations of only a few femtoseconds or even reaching the attosecond regime. This development has started the field of attosecond science which has enabled detailed studies of electron dynamics with a time resolution down to single attoseconds. In order to ultimately be able to control electrons and their motion with all-optical devices, it is a necessity to fully understand the fundamentals of light-matter and electron-electron interaction on this time scale. Double ionization of helium provides the ideal testbed to obtain insights into the electron dynamics in the full three-body Coulomb break-up process, as the process is simple enough such that ab-initio computations are numerically feasible. While the two extremal cases of few-photon and strong-field double ionization have been studied extensively, the regime in between where 4 to 20 photons are needed to overcome the double ionization threshold of helium has not gained a lot of attention. The reason for this is the numerical complexity and experimental limitations to generate intense light pulses for < 400 nm. Within this thesis we aim at bridging this gap starting from one-photon double ionization, increasing successively the wavelength of the ionizing light field until we approach the experimentally strong-field regime. To do so we employ state of the art ab-initio simulations. To characterize the influence of electron-correlation onto the double ionization process, we study similarities and differences in the angular emission pattern over a broad range of wavelengths.