Superconductivity, superfluidity, Bose-Einstein condensation, and lase
r amplification are all examples of a general mechanism involving the
stimulated transfer of bosons into a specific quantum state. When the
occupation number of the state is large, this mechanism may generate a
macroscopic coherence for the state amplitude. In this paper, we demo
nstrate that the stimulated transfer of bosonic atoms into a given sta
te of an optical or a magnetic trap can give rise to a coherent atomic
source in analogy with the photon laser and we present a general mode
l for such a device.