Controlled opacity in a class of nonlinear dielectric media
  Motivated by new technologies for designing and tailoring metamaterials, we seek properties for certain classes of nonlinear optical materials that allow room for a reversibly controlled opacity-to-transparency phase transition through the application of external electromagnetic fields. We examine some mathematically simple models for the dielectric parameters of the medium and compute the relevant geometric quantities that describe the speed and polarization of light rays. 
Eduardo Bittencourt, Guilherme Camargo, Vitorio A. De Lorenci and   Renato Klippert
physics.optics gr-qc