Abstract: Method and apparatus for generating electromagnetic energy by creating a population inversion between upper and lower energy levels in a target substance. The population inversion is maintained by exciting the individual particles to a short lived resonant negative ion-like state and then to a particular neutral state at a rate greater than the total rate of decay from the resonant negative ion-like state to the various lower energy levels. Particles in the resonant negative ion-like state decay quickly to at least two energy states at differential rates, with decay to the upper energy state occurring at a rate sufficiently greater than decay to the lower energy state to ensure population inversion. Atoms or molecules in the upper state decay to the lower state, emitting coherent radiation of a predetermined frequency and wave length.