Introduction

As we saw in Chapter 5, electromagnetic waves in isotropic materials are transverse, their electric and magnetic field vectors E and H being normal to the direction of propagation k. The direction of E or rather, as we shall see later, the electric displacement field D, is called the polarization direction, and for any given direction of propagation there are two independent such vectors, which can be in any two mutually orthogonal directions normal to k. When the medium through which the wave travels is anisotropic, which means that its properties depend on orientation, the above statements meet with some restrictions. We shall see that the result of anisotropy in general is that the fields D and B remain transverse to k under all conditions, but E and H, no longer having to be parallel to D and B, are not necessarily transverse. Moreover, the two independent polarizations that propagate must now be chosen specifically with relation to the axes of the anisotropy. A further direct consequence of E and H no longer being necessarily transverse, is that the Poynting vector Π = E × H may not be parallel to the wave-vector k.

In this chapter, we shall first discuss the various types of polarized radiation that can propagate. We shall then go on to extend the theory of electromagnetic waves as described in Chapter 5 to take into account anisotropic media.