An Etymological Dictionary of Astronomy and Astrophysics

The process by which an electron, which is already in an excited state (an upper energy level, in contrast to its lowest possible level or “ground state”), can “stimulate” a transition to a lower level, producing a second photon of the same energy. The quantum energy of the incoming photon should be equal to the energy difference between its present level and the lower level. This process forms the basis of both the → laser and → maser. Same as → induced emission.

See also: Stimulated, p.p. of → stimulate; → emission.