Locking of two modes with orthogonal elliptic polarisations in a gas laser

Expressions are obtained for a nonlinear polarisation of the medium in a gas laser operating under the conditions of locking of two modes with orthogonal elliptic polarisations. An analysis is made of the influence of their ellipticity on the frequency limit of locked operation and on the polarisation of the output radiation. Comparable experimental results for the 3.3912 and 3.3922 μm lines emitted by an He–Ne laser are shown to be in quantitative agreement with the theory, if the square of the ratio of the axes of the eigenpolarisation ellipses of the cavity is assumed to be ~0.02.