Suppression of coherent population trapping upon spontaneous decay of an excited state

The interaction of a model three-level Λ system with electromagnetic radiation is considered under the conditions where a coherence (an off-diagonal matrix element) between lower sublevels arises upon spontaneous decay of an excited state. The cases of bichromatic and incoherent broadband fields are analyzed. It is shown that the occurrence of coherence may significantly change the character of evolution of the system under study with time. These changes are most pronounced for broadband fields. Some features of this phenomenon are considered for multilevel atomic systems.