Coherence Effects in Gaseous Lasers with Axial Magnetic Fields. II. Experimental

Abstract

The rotation of the plane of polarization with an axial magnetic field on a short single-mode He-Ne planar-type laser has been studied experimentally. The study is concerned with regions of magnetic field where the beat frequency between the orthogonal circularly polarized oscillations approaches zero. A mutual synchronization of these otherwise independent oscillations then occurs over a range of magnetic field, resulting in a single frequency of oscillation in which the polarization remains linear but rotates. In near-zero magnetic field, rotations up to $\frac{1}{4}\pi$ are observed and may occur with magnetic fields less than 0.1 G. Results are given on the rotation versus magnetic field as a function of the laser intensity, the cavity tuning within the Doppler linewidth, the total gas pressure, and the anisotropy in the cavity losses. The observed rotation increases with the intensity and decreases with cavity detuning, with increasing total gas pressure, and with increasing anisotropy in the cavity $Q$. On attaining a rotation of $\frac{1}{4}\pi$, a transition region of magnetic field between the linear and circularly polarized regions is observed. The beat signal from the orthogonal circularly polarized waves then shows a high harmonic content due to transient behavior, which gives way to a single beat as the magnetic field is increased. Other such coherence regions are observed at magnetic fields of 10 G or more, where the observed beat frequency again approaches zero. Here the polarization again becomes linear and rotations similar to those in near-zero magnetic field are observed.