Coherence and correlations in photoinduced Auger and fluorescence cascades in atoms

An overview of the recent experimental and theoretical works on photoinduced cascades of Auger and fluorescence transitions in atoms is presented. We concentrate on the angular correlation and polarization phenomena in such cascades and how they are related to the alignment and orientation of the core-excited or core-ionized atomic states produced in the photoabsorption. During the decay, the alignment and orientation are then transferred to the energetically lower atomic states, causing an anisotropy and polarization of the subsequent Auger or fluorescence emission. Special attention is paid to the practically important case of overlapping resonances and intermediate states. Coherent excitation of the resonances and the coherence transfer in the decay strongly influence the angular and polarization characteristics of the decay products. The studies on the angular correlations and polarization of the emitted particles provide detailed spectroscopic and dynamic information about the transitions involved. In some cases, moreover, a so-called ‘complete’ experiment, i.e. the experimental determination of the transition amplitudes including their relative phases, becomes possible.