Abstract
Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. The process of autoionization, induced by resonant excitation of electrons into discrete states present in the spectral continuum of atomic and molecular targets, is mediated by electron correlation. Here we investigate the attosecond photoemission dynamics in argon in the 20–40 eV spectral range, in the vicinity of the 3s−1np autoionizing resonances. We present measurements of the differential photoionization cross section and extract energy and angle-dependent atomic time delays with an attosecond interferometric method. With the support of a theoretical model, we are able to attribute a large part of the measured time delay anisotropy to the presence of autoionizing resonances, which not only distort the phase of the emitted photoelectron wave packet but also introduce an angular dependence.
Highlights
Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems
We demonstrate how the angular dependence of the atomic time delays is affected by correlation effects associated to the mechanism of autoionization, giving access to angleresolved multi-electron dynamics on the attosecond time scale
The two experiments are both based on the RABBIT technique, but using different detection setups presented in details in the Methods section
Summary
Electron correlation and multielectron effects are fundamental interactions that govern many physical and chemical processes in atomic, molecular and solid state systems. In the simplest case, when the electron is promoted into a flat (non-resonant) continuum by direct laser-assisted photoionization, the measured delay after absorbing a single XUV photon is related to the phase shifts of the departing electron induced by the ionic potential and laser field, respectively One part of this socalled atomic time delay is the Wigner delay[4,5], which can be expressed as the energy derivative of the scattering phase and is equivalent to the group delay of the departing electron wave packet. The interference between the direct and autoionizing pathways gives rise to the well-known Fano profiles in the photoionization cross sections[23], which have been directly measured in atoms[24] and molecules[25] with high precision using for instance monochromatic synchrotron radiation Despite their value, these studies are unable to access the correlated dynamics of the photoionized resonant electron wave packet. The observed time delay anisotropy was attributed to phase differences between final quantum states with different angular symmetry resulting from twophoton (XUV+IR) ionization
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