  The spectroscopic properties of a single, tightly trapped atom are studied,
when the electronic levels are coupled by three laser fields in an $N$-shaped
configuration of levels, whereby a $\Lambda$-type level system is weakly
coupled to a metastable state. We show that depending on the laser frequencies
the response can be tuned from coherent population trapping at two-photon
resonance to novel behaviour at three photon resonance, where the metastable
state can get almost unit occupation in a wide range of parameters. For certain
parameter regimes the system switches spontaneously between dissipative and
coherent dynamics over long time scales.
