Broadening mechanisms in semiconductor (GaAs) lasers: Limitations to single mode emission

A model for the nature of line broadening was developed, explaining the incomplete saturation of spontaneous emission above threshold, the energy dependence of the radiative lifetime spectra, and the observation on homogeneous and inhomogeneous broadening behavior of semiconductor lasers operated with an external cavity. The agreement between the predictions and experimental observations lends credence to the model. The asymptotic nature of threshold is explained, and the increasing power and coherent nature of the emission as the gain approaches the loss are discussed. The observed multimode spectra in the vicinity of threshold reflects power sharing among the modes. The gain profile for various dopings and injections and the power emission spectra of the modes as a function of their gain were calculated.