Diffraction phenomena in ring gas lasers

The frequency and amplitude diffraction nonreciprocity of counterpropagating waves in a ring gas laser is studied. The self-consistent eigenmode problem is solved within the framework of the model of Gaussian beams for a ring optical resonator containing a nonlinear gaseous medium and a model aperture. The expressions for frequency-dependent losses, frequencies and intensities of counterpropagating waves are obtained and analysed. Experimental data on the influence of diffraction phenomena on the frequencies and intensities of counterpropagating waves reported in the literature are analysed. Nonreciprocal effects related to diffraction are classified by comparing the experimental data with theoretical results. The mechanisms of the asymmetry of the lasing region with respect to the central frequency of the transition and asymmetry of the laser line are explained.