On the theory of polarization effects in gas lasers

An analysis of polarization phenomena in a gas laser is presented. A Fabry-Perot resonator with plane-parrallel mirrors is investigated considering laser operation as the excitation of the natural modes of an open-resonator system. It is shown that in the case of weakly anisotropic mirrors, the natural modes can be grouped in pairs, so that each pair corresponds to one scalar longitudinal mode. The polarization preference in a single-mode laser is studied taking into account different relaxation constants for the density matrix; equations describing the time evolution of the polarization parameters of both modes in a two-mode operating gas laser are derived showing that mode-mode interaction results in modes whose polarizations are mutually orthogonal. Finally, the influence of small anisotropies on the degree of polarization of a single-mode laser is investigated when the latter is polarized with a transverse magnetic field.