Population inversion atoms in the ground and excited states are equal, the rate of stimulated emission is equal to the rate of absorption for a given radiation density. The critical detail of stimulated emission is that the induced photon has the same frequency and phase as the incident photon. In other words, the two photons are coherent. It is this property that allows optical amplification, and the production of a laser system. During the operation of a laser, all three light-matter interactions described above are taking place. Initially, atoms are energized from the ground state to the excited state by a process
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