Photogeneration of hollow atoms: Recent developments

Multiply-excited neutral atoms, or nearly neutral ions, with empty or only sparsely populated inner shells are termed "hollow atoms". Hollow atoms can be created in a variety of ion collision experiments. An alternative metho d of generation is to use photo-excitation. The first photogeneration of ho llow atom triply-excited states in neutral lithium was reported in 1994. Th e production of such triply-excited states is completely dependent on elect ron-electron correlations and their study has proved a challenge to both ex perimentalists and theorists. Results of recent experiments on hollow atoms carried out at synchrotron facilities in Europe, the USA and Japan are sum marised and comparisons made with various theoretical predictions.