Mode Interaction in a Zeeman Laser

Abstract

The interaction between modes of a short He-Xe laser using the $J=1\mathrm{}\to 0$ transition at 2.65 μ is investigated in an axial magnetic field. In zero field an elliptically polarized output usually predominates, with orientation and eccentricity changing with conditions and reflector characteristics. Neutral coupling occurs here; consequently, the system is sensitive to perturbations, in agreement with the observed erratic behavior. Small axial magnetic fields produce circular polarizations, quenching, and hysteresis effects between the two Zeeman oscillations arising from the frequency splitting of a single axial mode. A strong interaction, including sharp crossover regions in the intensities and quenching phenomena, is observed between two axial modes oscillating on well-resolved oppositely circularly polarized Zeeman components. The phenomena are studied as a function of cavity tuning, laser intensity, pressure, and magnetic field. No hysteresis was observed in the interaction between axial modes. The axial-mode intensities are equal for all positions of cavity tuning when the Zeeman separation equals the axial-mode interval. For small deviations of magnetic field from this value, however, crossover and quenching effects appear, and this allows a precise determination of the $g$ value of the upper state. These effects are discussed on the basis of Lamb's theory and equations deduced for the interaction. The Doppler parameter $\mathrm{Ku}$ is about 100 Mc/sec for xenon, which is comparable with the natural linewidths, and requires a more exact discussion of the third-order atomic polarization terms. The results derived show some qualitative agreement with observations, particularly on the axial-mode interaction, which is discussed in detail.