  We study the temporal evolution of a three-level system (such as an atom or a
molecule), initially prepared in an excited state, bathed in a laser field
tuned at the transition frequency of the other level. The features of the
spontaneous emission are investigated and the lifetime of the initial state is
evaluated: a Fermi "golden rule" still applies, but the on-shell matrix
elements depend on the intensity of the laser field. In general, the lifetime
is a decreasing function of the laser intensity. The phenomenon we discuss can
be viewed as an "inverse" quantum Zeno effect and can be analyzed in terms of
dressed states.
