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Relativistic quantum dynamics in strong fields: photon emission from heavy, few-electron ions

Recent progress in the study of the photon emission from highly charged heavy ions is reviewed. These investigations show that high-Z ions provide a unique tool for improving the understanding of the electron–electron and electron–photon interaction in the presence of strong fields. Apart from the bound-state transitions, which are accurately described in the framework of quantum electrodynamics, much information has also been obtained from the radiative capture of (quasi-) free electrons by high-Z ions. Many features in the observed spectra hereby confirm the inherently relativistic behaviour of even the simplest compound quantum systems in nature.