Polarization stability and dynamics in a model for a polarization-isotropic laser that goes beyond third-order Lamb theory

Instabilities and dynamical pulsations are common features of solutions of a model that includes the material variable dynamics for a laser with a polarization isotropic resonator and with a homogeneously broadened j=1{→}j=0 transition. These resemble in some respects features found in third-order Lamb theories under anisotropic conditions, such as splitting of the optical field into two relatively independent orthogonally polarized modes with different optical frequencies. At higher intensities the amplitudes and frequencies of these modes exhibit such strong coupling that a ``two-mode'' description loses its usefulness or effectiveness. Various periodic attractors with strong intensity and polarization pulsations are found for moderate excitation levels. Some of these attractors preserve the breaking of the polarization isotropy on average just as does any linearly polarized solution. But in some cases the dynamics restore the polarization isotropy on average. We also find other dynamical phenomena, including periodic and apparently chaotic states, often involving rapid switching between long interludes of nearly constant polarization, and homoclinic behavior. {} 1996 The American Physical Society.