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 eigenstates of the Hamiltonian as well. These states are equally spaced both in energy and real space and form the so-called Wannier-Stark ladder. In the proposed scheme, an application of an electrical bias to a semiconductor superlattice is increasing the amplitude of coherent folded phonons generated by an optical pulse. This increase of the amplitude is observed for those biases in which the energy drop per period of the superlattice is greater than the phonon energy. If the superlattice is biased such that the energy drop per period of the superlattice exceeds the width of electronic minibands (Wannier-Stark regime), the