Computer-simulated transient evolution of 1.55µm laser spectra

The transient evolution of 1.55µm-wavelength laser spectra has been calculated from numerical solution of the multimode rate equations including the effects of spontaneous emission into the modes. A simple analytical model for gain spectrum has been used which assumes recombination between parabolic bands with no k-selection. The results show the characteristic relaxation oscillations in each mode together with competition effects between the modes which occur with a rather slower time scale. The principal parameter which determines the power sharing and competition between the modes is the displacement in wavelength of the steady-state peak gain from the nearest Fabry-Perot mode. The relaxation oscillations and modal competition are shown on a 16mm cine film in a form that can be readily assessed