Light-induced drift in cascade excitation of levels

An analysis is made of a light-induced drift observed under cascade excitation of atomic levels. A detailed description is given of the drift in the case of absorption of monochromatic and quasimonochromatic radiation as a result of a transition between the excited states. Preliminary excitation is provided either by broad-band radiation or by traditional nonlaser methods. It is shown that the drift is possible also when the transport cross sections of the particles which are at the active levels (involved in a transition under the action of resonance monochromatic or quasichromatic radiation) are identical: a difference between the transport cross sections for any pair of levels is sufficient for the occurrence of the drift.