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 \ensuremath{\mu}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.
Anisotropy parameters describing the angular dependence of the photoionization delay are defined. The formalism is applied to results obtained with the relativistic random phase approximation with exchange for photoionization delay from the outermost
s-orbitals in selected rare-gas atoms. Any angular dependence in the Wigner delay is induced here by relativistic effects, while the measurable atomic delay exhibits such a dependence also in the nonrelativistic limit. The contributions to the anisotropy from the different sources are disentangled and discussed. For the heavier rare gases, it is shown that measurements of the delay for electrons ejected in specific angles, relative to, e.g., those ejected along the laser polarization, are directly related here to the Wigner delay. For a considerable range of angles, the contributions from the second photon largely get canceled when the results in different angles are compared, and this angle-relative atomic delay is then close to the corresponding Wigner delay.