Competition between high-intensity modes of different polarizations in a gas laser

A theoretical analysis is made of the stability range of stimulated emission of two modes with orthogonal and parallel polarizations. The case of transitions between active levels of momenta j_a = j_b = 1 in a relatively strongly excited medium is considered. It is found that, in contrast to the case of parallel polarizations, emission of two modes with orthogonal polarizations is possible even when the mode spacing is small. Investigation is made of the influence of the quadrupole polarization of the medium on the width of the two-mode emission range. It is shown that the results obtained by calculating the polarization of the medium to within terms cubic in respect of the field amplitude describe correctly relatively highly excited active media.