Sound amplification by stimulated emission of radiation frequencies ) of the phonons as a function of their wave vector's "k" . The relationship between frequency "ω" and wave vector "k" is called phonon dispersion. Light and sound are similar in various ways. They both can be thought of in terms of waves, and they both come in quantum mechanical units. In the case of light we have photons while in sound we have phonons. Both sound and light can be produced as random collections of quanta (e.g. light emitted by a light bulb) or orderly waves that travel in a coordinated form (e.g. laser light). This parallelism
Stimulated emission quantum theory, wherein the emission is described in terms of photons that are the quanta of the EM field. Stimulated emission can also occur in classical models, without reference to photons or quantum-mechanics. (See also Laser#history ) Stimulated emission can be modelled mathematically by considering an atom that may be in one of two electronic energy states, a lower level state (possibly the ground state) (1) and an "excited state" (2), with energies "E" and "E" respectively. If the atom is in the excited state, it may decay into the lower state by the process of spontaneous emission, releasing the