Spontaneous emission suppression on arbitrary atomic transitions
  We propose a very simple scheme to slow down the usual exponential decay of upper state population in an atomic two level system considerably. The scheme makes use of an additional intense field with frequency lower than the total decay width of the atomic transition. This allows for additional decay channels with the exchange of one or more low-frequency photons during an atomic transition. The various channels may then interfere with each other. The intensity and the frequency of the low-frequency field are shown to act as two different control parameters modifying the duration and the amount of the population trapping. An extension of the scheme to include transitions to more than one lower state is straightforward. 
Joerg Evers, Christoph H. Keitel