Observation of radiation instabilities of a two-mode He-Ne laser with the help of interference of polarized rays

Instabilities in the operation of a two-mode He-Ne laser are observed with the help of interference of polarized beams. Two interference patterns created by two radiation modes alternatively appear. The contrast of the interference pattern increases under the action of an external constant magnetic field on the laser. If one of the interfering beams is delayed sufficiently long, the instability manifests itself in the motion of interference fringes in a direction that depends on which of the two beams is delayed. The particular features of the evolution of the interference pattern are explained based on interference equations for the two modes that take into account the orthogonality of the linear polarizations of the modes, as well as changes in their amplitudes and frequencies.