Polarization dynamics in a transverse multimode class b laser: Role of the optical feedback

We investigate the polarization dynamics in a quasi-isotropic CO
2
laser emitting on the annular mode subjected to an optical feedback. We observe a complex dynamics in which spatial mode and polarization competition are involved. The observed dynamics is well reproduced by a model that discriminates between the intrinsic asymmetry due to the kinetic coupling of molecules with different angular momenta and the anisotropy induced by the polarization feedback. We observe various dynamical regimes including chaotic dynamics and show that feedback changes these states from regular to chaotic and vice versa. Such a dynamics is also accompanied by spontaneous between the patterns that indicate the existence of bistability in the system. Finally the possible applications to polarization coding are discussed.