The model of the optical switching center and the polarization anomalies   in absorption spectra of cupric oxide after fast particles irradiation
  We consider the model of the optical switching center - a system with the following properties: It has two (or more) metastable states |1>, |2>, separated by a potential barrier U; it can switch from one state to another by absorbing the photons with energy proportional to U; the transition from |1> to |2> is allowed only for a certain light wave polarization p_1 and the transition from |2> to |1> - for other polarization p_2; these polarizations p_1, p_2 are orthogonal. The optical properties of this system are studied and are found to exhibit unconventional polarization dependence. In particular, the absorption spectrum observed in natural (unpolarized) light can display new features, that are absent in the spectra, obtained in two independent polarizations. We discuss these results in connexion with the (yet unexplained) experimental findings (Ref.1), where the similar anomalous polarization dependence of the absorption spectra of cupric monoxide CuO after the fast particle bombardment is reported. 
E.V. Zenkov