We investigate the polarization properties of the annular pattern in a
CO2 laser designed to preserve a good cylindrical symmetry. We found
that this pattern can show two different polarization states. The firs
t one corresponds to a superposition of two independent Gauss-Hermite
modes with linear and orthogonal polarizations. The second one is a li
nearly polarized state. A simple model, including anisotropies both fo
r the cavity losses and the detuning, can explain the observed transit
ion between these two states. We also provide an interpretation of the
interplay between polarization states and corresponding spatial patte
rns. (C) 1997 Elsevier Science B.V.