Thesis manuscript
This thesis deals with the study of ultrafast photo-induced processes in atoms on the attosecond time scale (1as = 10-18s). The aim was to resolve the electronic dynamics of the resonant photoionization process in both space and time.
To this end, work focused on the study of 2-photon ionization (XUV IR) of helium through bound states close to the 1sNp ionization threshold (N=3,4,5,6). The electronic dynamics of ionization were resolved temporally and spatially by combining an electron wave packet interferometry technique with angularly resolved photoelectron spectroscopy. The resonant 2-photon transition was probed using two different interferometric schemes.
In the first scheme, called RABBIT, the resonant electron wave packet (EWP) was characterized through its interference with a second non-resonant 2-photon EWP used as a reference. The 3D spatial structure of the POE was reconstructed, along with its temporal evolution. Transient trapping on the bound states induces a delay in POE emission, and its spatial structure is preserved throughout the photoemission dynamics.
The second interferometric scheme used in this thesis provides direct access to the 2-photon transition dynamics of resonant POE. It is based on interference between the resonant POE and that resulting from two sequential 1-photon transitions. The latter exhibits a slow phase spectral evolution, making it an ideal reference. This scheme was used to characterize POE dynamics for all 1sNp intermediate states, thus extending the previous study. Photoemission dynamics and spatial dependence have been characterized, and the results are consistent with the first scheme for the 1s3p and 1s4p states. This second scheme offers absolute spectral calibration, better spectral resolution and higher sensitivity than the RABBIT scheme.
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