Chiral multi-electron emission

In this report we review recent progress in the understanding of the role o f chirality in the multi-electron emission. A brief account of the chiral s ingle-electron photoemission is given. In this case the chirality of the ex perimental set-up is brought about by an initial orientation of the target or/and by specifying a certain projection of the photoelectron spin. The de pendence of the photoelectron spectrum on the chirality of the experiment i s probed by changing the initial orientation of the target or by inverting the photoelectron spin projection. In a further section we envisage the dir ect transition of chiral electron pairs from an isotropic bound initial sta te into a double-continuum state following the absorption of a circularly p olarised photon. We work out the necessary conditions under which the spect rum of the correlated photoelectron pair shows a chiral character, i.e. a d ependence on the chirality of the exciting photon. The magnitude and the ge neral behaviour of the chiral effects are estimated from simple analytical models and more elaborate numerical methods are presented for a more quanti tative predictions. As a further example for the chiral multi-electron emis sion we study the photoelectron Auger-electron coincidence spectrum. The Au ger hole is created by ionising a randomly oriented target by a circular po larised photon. We investigate how the helicity the photon is transferred t o the emitted photoelectron pair. The theoretical findings are analysed and interpreted in light of recent experiments. In a final section we focus on the emission of correlated electrons where the initial state is already or iented, e.g. via optical pumping by circularly polarised light. The initial orientation of the atom is transferred to the continuum states following t he ionisation of the target by low-energy electrons. We formulate and analy se the theoretical concepts for the transition of the screw sense of the in itially bound atomic electron to the continuum electron pair. Numerical met hods for the calculations of the cross-sections for the electron-impact ion isation of oriented atoms are presented and their results are contrasted ag ainst recent experimental data. (C) 2001 Elsevier Science B.V. All rights r eserved.