Observation of bistable behavior in the polarization of a laser

The output of a single-mode He-Ne laser with internal mirrors is usually linearly polarized in one of two orthogonal directions. This polarization state may be selected by a tunable injected signal or by feedback from a tunable secondary optical resonator. The laser will remain in the selected polarization even after the injected signal or the feedback from the secondary resonator is removed. This effect has potential applications as a fast switch or as an optical memory. An explanation based on intracavity birefringence is given for this bistable behavior in the polarization.