Combination Mode-Mode Coupling as an Instability Mechanism in a Dye Ring Laser

The low-frequency time-dependent processes observed in the spectra of class A and class B lasers (according Arecchi [1]) can’t be explained using the rate equations. However, by introducing other nonlinear processes of mode coupling in addition to the laser medium saturation one gets a deeper insight into the nature of the multimode laser instability. There was a successful attempt in ref. [2] to take into account the influence of mode coupling on laser action via stimulated Brillouin scattering. However, it should be natural to seek for the reason of the nonlinear mode coupling in the laser medium itself. In the next high-order approximation of the dynamical theory of laser with adiabatically eliminated polarization, the combination mode-mode coupling (CMMC) due to the mode- induced inversion oscillations is taken into account [3-5].