POLARIZATION SWITCH IN A ZEEMAN LASER IN THE PRESENCE OF DYNAMICAL INSTABILITIES

The well-known switch of the polarization state of a Zeeman laser's em ission into a single longitudinal mode as the cavity length is detuned is re-examined using a model that goes beyond third-order Lamb theory by retaining equations for the dynamics of the material variables for a J=1 to J=0 transition. For certain parameter values, the output of the laser as described by this model is predominantly two orthogonally polarized modes with different optical frequencies, as in third-order Lamb theories studied previously, but the more complicated field-mate rial dynamics and near-threshold time-dependent solutions present in t his model also give rise to more complicated pulsations and polarizati on dynamics as the cavity is detuned. Also as in third-order Lamb theo ries, in this model the preference (stability) for circularly or linea rly polarized single mode emission depends on the ratio of the decay r ates of the magnetic dipole and the electric quadrupole of the J=1 lev el. For conditions in which the cross-saturation preference is for lin early polarized emission and there are weak linear anisotropies, the s witching of the polarization state as the cavity is detuned has a rang e of overlap of the two polarization states (and corresponding time de pendent dynamics) rather than the abrupt switching and hysteresis or p olarization rotation more commonly found in simpler models, The detuni ng range for the overlap is sensitively dependent on the strength of t he cross-saturation coupling. While there is similar exchange of relat ive dominance of two polarized modes when there is the combination of weak circular polarization anisotropies and cross-saturation preferenc e for linearly polarized emission, the overlap region remains large, a nd it is relatively independent of the relaxation rate of the coherenc e between the upper levels. By comparing these results with experiment al behavior found in a xenon laser which operates on a J=3 --> J=2 tra nsition we can estimate the effective parameters of the model suitable for describing certain features of this experimental situation, even though the xenon laser is known to have its preference for linearly po larized emission arise directly in the field-matter interaction rather than solely from relaxation rate differences as it does in the model considered here.