Sound amplification by stimulated emission of radiation the axes of the mirrors, it is possible for photons to repeat multiple reflections and force more and more photons to follow them producing an avalanche effect. The number of photons of this coherent laser beam increases and competes the number of photons perished due to losses. The basic necessary condition for the generation of a laser radiation is the population inversion, which can be achieved either by exciting atoms and inducing percussion or by external radiation absorption. A SASER device mimics this procedure using a source-pump to induce a sound beam of phonons. This sound beam propagates not in
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