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Schlagwörter:
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Zusammenfassung:
Time-resolved phase-contrast imaging using ultrafast x-ray sources is an emerging method to
investigate ultrafast dynamical processes in matter. Schemes to generate attosecond x-ray
pulses have been proposed, bringing electronic timescales into reach and emphasizing the
demand for a quantum description. In this paper, we present a method to describe
propagation-based x-ray phase-contrast imaging in nonrelativistic quantum electrodynamics.
We explain why the standard scattering treatment via Fermi’s golden rule cannot be applied.
Instead, the quantum electrodynamical treatment of phase-contrast imaging must be based on
a different approach. It turns out that it is essential to select a suitable observable. Here, we
choose the quantum-mechanical Poynting operator. We determine the expectation value of our
observable and demonstrate that the leading order term describes phase-contrast imaging. It
recovers the classical expression of phase-contrast imaging. Thus, it makes the instantaneous
electron density of non-stationary electronic states accessible to time-resolved imaging.
Interestingly, inelastic (Compton) scattering does automatically not contribute in leading
order, explaining the success of the semiclassical description.
