Lasing without inversion
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Lasing without inversion (LWI),[1] or lasing without population inversion, is a technique used for light amplification by stimulated emission without the requirement of population inversion.[2] A laser working under this scheme exploits the quantum interference between the probability amplitudes of atomic transitions in order to eliminate absorption without disturbing the stimulated emission.[3] This phenomenon is also the essence of electromagnetically induced transparency.[4]
The basic LWI concept was first predicted by Ali Javan in 1956.[5][6] The first demonstration of LWI was carried out by Marlan Scully in an experiment in rubidium and sodium at Texas A&M University, and then at NIST in Boulder.[7]