Polarization states of annular pattern in a nearly-isotropic laser resonator

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 first one corresponds to a superposition of two independent Gauss-Hermite modes with linear and orthogonal polarizations. The second one is a linearly polarized state. A simple model, including anisotropies both for the cavity losses and the detuning, can explain the observed transition between these two states. We also provide an interpretation of the interplay between polarization states and corresponding spatial patterns. (C) 1997 Elsevier Science B.V.