Sound amplification by stimulated emission of radiation be more conceivable by imagining it in analogy to laser theory. Theodore Maiman operated the first functioning LASER on May 16, 1960 at Hughes Research Laboratories, Malibu, California, A device that operates according to the central idea of the "sound amplification by stimulated emission of radiation" theory is the "thermoacoustic laser". This is a half-open pipe with a heat differential across a special porous material inserted in the pipe. Much like a light laser, a thermoacoustic SASER has a high-Q cavity and uses a gain medium to amplify coherent waves. For further explanation see thermoacoustic heat engine. The possibility of
Stimulated emission of energy levels 1 and 2, respectively. The intensity (in watts per square meter) of the stimulated emission is governed by the following differential equation: as long as the intensity "I"("z") is small enough so that it does not have a significant effect on the magnitude of the population inversion. Grouping the first two factors together, this equation simplifies as where is the "small-signal gain coefficient" (in units of radians per meter). We can solve the differential equation using separation of variables: Integrating, we find: or where The saturation intensity "I" is defined as the input intensity at which the