UNIQUE POLARIZATION CAUSED BY FREQUENCY LOCKING BETWEEN SIGMA-MODE AND PI-MODES IN A TRANSVERSE ZEEMAN LASER

Experiments on polarization characteristics of a single-longitudinal-m ode internal-mirror 633 nm He-Ne laser with very small cavity anisotro py have been performed. A polarization rotating phenomenon from the si gma to the pi mode direction and to directions other than the sigma or pi direction by varying magnetic field strength (2.7 to 9.0 mT) has b een observed. Here, polarization is independent of the natural axis, a nd this rotated polarization switches alternately between adjacent lon gitudinal modes with respect to the sigma mode axis. These alternating polarizations are not perpendicular to each other. The rotation and t he switching of polarization are unique. Furthermore, we have conducte d theoretical analyses on polarization characteristics under the stron g coupling condition of sigma and pi modes based on the theory of the transverse Zeeman laser. Then it is concluded that this unique polariz ation rotation is caused by the frequency locking of the two modes.