Sound amplification by stimulated emission of radiation 0.3 eV. For the same scheme, the usage of a semiconductor heterostructure (layers of different semiconductors) with narrow gap indirect in momentum space between valence and conduction bands may be more effective. This could be more promising since the spatial separation of the layers provides a possibility of tuning the interband transition into resonance by an external electric field. An essential statement here is that this proposed phonon laser can operate only if the temperature is much lower than the energy gap in the semiconductor. During the analysis of this theoretical scheme several assumptions were introduced for simplicity reasons. The
Sound amplification by stimulated emission of radiation exciton level is lower than the level of indirect exciton because of greater Coulomb interaction. Also, indirect exciton has an electric dipole momentum normal to coupled quantum well and thus a moving indirect exciton has an in-plane magnetic momentum perpendicular to its velocity. Any interactions of its electric dipole with normal electric field, lowers one of indirect exciton sub-levels and in sufficiently strong electric fields the moving indirect exciton becomes the ground excitonic level. Having in mind these procedures, one can select velocity to have an interaction between magnetic dipole and in-plane magnetic field. This displaces the minimum of the