Light propagation through polarizing systems

Abstract

We shall consider here light propagation through anisotropic materials or polarizing optical elements and systems, and shall describe in brief the methods used to find the changes in light intensity and polarization introduced by these anisotropic elements. Materials with optical anisotropy In anisotropic materials the velocity of light propagation depends on the propagation direction. The anisotropy is connected with the structure of the material. Typical materials with optical anisotropy are transparent crystals, and the theory of light propagation through anisotropic media is usually called crystal optics [1–3]. Optical anisotropy is also observed in liquid crystals, and in some amorphous materials subjected to external forces such as mechanical or electrical forces. Stretched polymer films provide a good example. In this book we deal mainly with photoinduced anisotropy. In some materials illumination with polarized light causes selective destruction of absorbing molecules or centers, reordering of these absorbing centers, or some other changes depending on light polarization. This results in polarization-dependent changes in the absorption coefficient or/and in the refractive index of the material, that is, in optical anisotropy. The dependence of the absorbance on light polarization is called dichroism and the dependence of the refractive index on light polarization is called birefringence . When a material is anisotropic, its dielectric permeability is a tensor, and as a consequence the wave surfaces in it are not spherical, but are ellipsoidal.