Sound amplification by stimulated emission of radiation (TA) phonons is better because TA phonons have lower energy and the greater life-time than LA phonons. Therefore, their interaction with the electronic subsystem is weak. In addition, simpler quantitative evaluations require a pumping of direct exciton level performed by a laser irradiation. A further analysis of the scheme can help us to establish differential equations for direct exciton, indirect exciton and phonon modes. The solution of these equations gives that separately phonon and indirect exciton modes have no definite phase and only the sum of their phases is defined. The aim here is to check if the operation of
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