Zeeman and Coherence Effects in the He-Ne Laser

Abstract

An account is given of further investigations of the Zeeman effect on the He-Ne laser transition at $\ensuremath{\lambda}=1.153$ \ensuremath{\mu}, using both planar- and confocal-type resonators. For Zeeman level separations larger than the natural linewidths, the specific polarizations of the Zeeman transitions for the appropriate geometry are observed in the planar laser. Low-frequency splittings of axial resonances associated with anomalous dispersion effects occur under these conditions, the polarizations of these being linear, or circular, and orthogonal. At values of magnetic field such that the Zeeman levels overlap, coherence effects in the induced radiation are made evident by the disappearance of such low-frequency beats and by changes in these polarizations. This is considered using the theory of the depolarization of resonance radiation by magnetic fields, and also using time-dependent perturbation methods. For a symmetrical location of the axial resonance within the Doppler-broadened line, linear polarization is predicted for axial magnetic fields such that the states overlap, and some experimental verification is given. Related effects occur in the confocal laser where the Brewster angle windows determine the polarization. Here oscillations may be inhibited, or modulated by axial magnetic fields. Dips in the power output of this laser occur at smaller magnetic fields and are presently associated with interference effects when the Zeeman levels overlap. Some indications are given of coupling effects at Zeeman separations corresponding to the frequency interval between axial resonances.