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Institute’s Seminar

Wednesday, 12/03/2014, 05:15 PM
Seminar room HI-Jena, Fröbelstieg 3
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Theory of attosecond delays in laser-assisted photoionization

Marcus Dahlström
CFEL Hamburg

This tutorial-talk presents an introduction to the interaction of light and matter on the attosecond timescale. My aim is to overview the theoretical description of ultra-short time-delays, and to relate these to the phase of extreme ultraviolet (XUV) light pulses and to the asymptotic phase-shifts of photoelectron wave packets. Special emphasis is laid on time-delay experiments, where attosecond XUV pulses are used to photoionize target atoms at well-defined times, followed by a probing process in real time by a phase-locked, infrared laser field. In this way, the laser field serves as a "clock" to monitor the ionization event, but the observable delays do not correspond directly to the delay associated with single-photon ionization. Instead, a significant part of the observed delay originates from a measurement induced process, which obscures the single-photon ionization dynamics. This phase-lag effect is traced back to a phase-shift of the above-threshold ionization transition matrix element, which we call the continuum--continuum phase.

It arises due to the laser-stimulated transitions between Coulomb continuum states. As we shall show here, these measurement-induced effects can be separated from the single-photon ionization process, using analytical expressions of universal character, so that eventually the attosecond time-delays in photoionization can be accessed. Finally, I will show results of atomic delay calculations performed using diagrammatic many-body perturbation theory.