Experimental and theoretical study of the anisotropy induced in a gas laser by a saturating field

The optical anisotropy induced by a saturating stationary field in a gas laser which is initially isotropic is described theoretically. The calculation of the polarizability tensor shows that linear or circular anisotropies can be induced depending upon the electromagnetic field polarization. The Jones matrix formalism is extended to the nonlinear case. The experimental verification of the predicted linear gain anisotropy in a He-Ne laser is obtained at 3.39 {μ}m. The Jones matrix for a probe field in this particular case is also calculated. The corresponding linear anisotropy is attributed to Zeeman coherences between sublevels. Moreover, we find that the maximum of this anisotropy is slightly shifted from the center of the line.