CHAPTER XI - ELECTROMAGNETIC WAVES IN ANISOTROPIC MEDIA

Abstract

The properties of an anisotropic medium with respect to electromagnetic waves are defined by the tensors, which give the relation between the inductions and the fields. The refraction of a plane wave incident on the surface of a crystal is different from refraction at the boundary between two isotropic media. The laws of refraction and reflection are obtained from the continuity of the component of the wave vector, which is tangential to the plane of separation. The wave vectors of the refracted and reflected waves lie in the plane of incidence. In a crystal, however, two different refracted waves are formed, a phenomenon known as double refraction or birefringence. They correspond to the two possible values of the normal component that satisfy Fresnel's equation for a given tangential component. In a uniaxial crystal, ordinary and extraordinary refracted waves are formed. The ordinary wave is entirely analogous to the refracted wave in isotropic bodies; in particular, its ray vector lies in the plane of incidence. The ray vector of the extraordinary wave does not lie in the plane of incidence. Besides the electric-optical and magnetic-optical effects, there are other ways in which the optical symmetry of a medium can be changed by external agencies. These include the effect of elastic deformations on the optical properties of solids. Such deformations may render an isotropic solid body optically anisotropic.