The decay of autoionising atomic states in a resonance electromagnetic field

The decay of an autoionising state (AS) is considered in the presence of a resonance electromagnetic field (EMF) connecting the AS with some other level. It is shown that if the EMF is switched on suddenly the process of decay can be characterised by two constants which depend on frequency, intensity and polarisation of the EMF. One of these constants is always more of about the order of the field-free autoionising width of the AS. However, if the EMF parameters obey some conditions the other decay constant can be much smaller than the field-free AS width. In this case the lifetime of the AS in the EMF as a whole can be much larger than the field-free lifetime of the AS, this means that there is a partial stabilisation of the AS. An increase in the AS lifetime is connected with a destructive interference between the autoionising and ionising transitions. However, there are always some 'non-interfering' transitions due to which stabilisation can never be absolute. The long living part of the AS population is shown to be rather small. If the EMF is switched on adiabatically there is only a simple one-exponential decay with only the characteristic decay time and there is no field-induced stabilisation.