Properties of Gaseous Optical Masers in Weak Axial Magnetic Fields

Abstract

The theory of a gaseous optical maser in a magnetic field, as derived by Sargent, Lamb, and Fork, was compared with experiment for the case of a single-spatial-mode, internal-mirror maser in an axial magnetic field. Under these circumstances the twofold polarization degeneracy of the cavity mode is broken down, and the maser tends to oscillate in the two oppositely circularly polarized components of the mode. The intensities and frequency difference of these two components were measured as functions of cavity length and magnetic field for $J=1\mathrm{}\to J=0\mathrm{}$ and $J=1\mathrm{}\to J=2\mathrm{}$ transitions in He-Ne optical masers. It was found that all of the qualitative features of the results were correctly predicted by the theory, and in many cases excellent quantitative agreement was found between theory and experiment. Two areas of disagreement were found. (1) The coupling between the two polarizations is somewhat stronger than that predicted by theory. This is very clear for a $J=1\mathrm{}\to J=0\mathrm{}$ transition, and may be present in the $J=1\mathrm{}\to J=2\mathrm{}$ transition. No completely satisfactory explanation of this effect has been given. (2) The calculated frequency difference for the $J=1\mathrm{}\to J=2\mathrm{}$ transition appears to be smaller than that found in the experiment, although theory and experiment are in good agreement for the $J=1\mathrm{}\to J=0\mathrm{}$ transition. The effects, of small anisotropies in the cavity, on both the intensities and frequency difference were studied, and it was found that the theoretical results are in excellent agreement with experiment.