Emission of a single elliptic mode from a gas laser

Equations describing the emission of a single elliptically polarized mode from a gas laser are derived and investigated. The elliptic polarization is frequently observed experimentally when a tube with an active medium is placed inside a Fabry–Perot resonator between two phase plates with nearly quarter-wave properties. The condition for the existence of an elliptically polarized mode is derived for a resonator containing an active medium.