The (e,2e) spectroscopy, achievements and perspectives

Abstract
Electron-electron coincidence experiments have experienced over the past twenty years an increasingly rapid expansion and application to many different fields. Among them, the (e,2e) spectroscopy has been successfully used to investigate either the target electronic structure or the ionisation dynamics. The capability of this spectroscopy to investigate single particle properties in atoms, molecules and solids is discussed by the help of some recent results. Correlation effects in bound states and in the continuum have been the subject for several recent (e,2e) investigations. Single and double ionisation coincidence experiments are reviewed focusing the attention on correlation effects. The interference between direct and resonant ionisation channels has been also the objective of recent electron coincidence experiments. Perspective and developments of the (e,2e) spectroscopy are briefly discussed.