Abstract

Side-mode gain and coupling coefficients in semiconductor laser media are calculated with the use of a multimode Fourier technique valid both for mode spacings that are small compared with the carrier–carrier relaxation rates and for spacings comparable with these rates as predicted by the Boltzmann theory of Binder et al. [ Phys. Rev. B 45, 1107 ( 1992)]. The medium is described by a free-carrier model that provides for carrierprobability pulsations around quasi-equilibrium Fermi–Dirac values. We find that population pulsations play just as important a role as spectral hole burning for mode spacings comparable with the intraband relaxation rates. For the carrier–carrier relaxation rates of Binder et al., side-mode gain is predicted to be smaller than the main-mode gain, leading to single-mode operation. However, for somewhat smaller intraband relaxation rates, side-mode gain is readily found that exceeds the single-mode gain, which would encourage multimode operation. In addition, we find that the gain and coupling coefficient spectra are sensitive to the k dependence of the carrier—carrier relaxation rates and might provide a useful way to measure these rates. We are also able to explain the asymmetric side-mode gain spectra for small beat frequencies in terms of the rapid decrease of the quasi-equilibrium Fermi–Dirac electron distribution just above the gain region.

© 1992 Optical Society of America

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