Light Polarization of a Quasi-isotropic Laser with Optical Feedback

The light of a quasi-isotropic, single-mode gas laser is linearly polarized for a line Jₐ=1→Jb=2. However, the azimuth of polarization can vary inside the line. Among the many different effects which cause these variations, we describe the role played by the detector optical feedback. We show experimentally that its amplitude and phase can be varied in a controlled manner in order to obtain abrupt switches between two perpendicular polarization states. Polarization bistability and hysteresis effects can then be commanded and studied from the outside of the laser.