Sound amplification by stimulated emission of radiation phonon laser action had been proposed in a wide range of physical systems such as nanomechanics, semiconductors, nanomagnets and paramagnetic ions in a lattice. Finding materials that stimulate emission was needed for the development of the SASER. The generation of coherent phonons in a double-barrier semiconductor heterostructure was first proposed around 1990. The transformation of the electric potential energy in a vibrational mode of the lattice is remarkably facilitated by the electronic confinement in a double-barrier structure. On this basis, physicists were searching for materials in which stimulated emission rather than spontaneous emission, is the dominant decay process. A device
Sound amplification by stimulated emission of radiation is possible. In a two level system, the particles have only two available energy levels, separated by some energy difference: "ΔΕ = E - E = hv" where "ν" is the frequency of the associated electromagnetic wave of the photon emitted and "h" is the Planck constant. Also note: "E" > "E". These two levels are the excited (upper) and ground (lower) states. When a particle in the upper state interacts with a photon matching the energy separation of the levels, the particle may decay, emitting another photon with the same phase and frequency as the incident photon. Therefore, by