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 an atomic or molecular resonance, the spectral line shape function is described as a Lorentzian distribution where formula_12 is the full width at half maximum or FWHM bandwidth. The peak value of the Lorentzian line shape occurs at the line center, formula_13. A line shape function can be normalized so that its value at formula_9 is unity; in the case of a Lorentzian we obtain Thus stimulated emission at frequencies away from formula_9 is reduced by this factor. In practice there may also be broadening of the line shape due to inhomogeneous broadening, most notably due to the Doppler effect