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 in the system leads to both the appearance of a backward wave and a dynamical instability of the system. Mathematical analyses have shown that two types of losses must be overcome for generation of oscillations to start. Losses of the first type are associated with the dispersion of energy inside the active medium and second type losses are due to radiation losses at the ends of the resonator. These types of losses are inversely proportional to the amount of energy stored in the resonator. In general, the disparity of the radiators does not play a role in any attempt of