Sound amplification by stimulated emission of radiation despite the difference in phonon and exciton dimensionalities. Phonon laser action has been stated in a wide range of physical systems (e.g. semiconductors). A 2012 publication from the Department of Applied Physics in California Institute of Technology (Caltech), introduces a demonstration of a compound micro-cavity system, coupled with a radio-frequency mechanical mode, which operates in close analogy to a two level-laser system. This compound micro-cavity system can also be called ""photonic molecule"". Hybridized orbitals of an electrical system are replaced by optical supermodes of this photonic molecule while the transitions between their corresponding energy levels are induced by a phonon
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