On the Theory of Laser Action in Dense Exeiton Systems

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Abstract
The rate equations for the exciton‐exciton (ex‐ex), exciton‐electron (ex‐e) and exciton‐hole (ex‐h) recombination processes are derived by taking into account polariton effects. The solutions of the stationary rate equations yield the spectra of the spontaneous emission and of the gain. Their temperature‐dependent shifts are calculated by taking into account self‐energy corrections which improve the agreement with experiment. Furthermore, the various threshold pump rates are calculated. Due to these results it is expected that the laser action should start at low temperatures for the ex‐ex process, at intermediate temperatures for the ex‐LO phonon process (which has been treated previously), and at high temperatures for the ex‐e process. The temperature ranges in which the nonlinear recombination processes (ex‐ex, ex‐e) have the lowest threshold increase with decreasing resonator quality. Numerical results arc given for example for CdS.