Optical properties that indicate symmetry in a crystal

2 Optical properties that indicate symmetry in a crystal 

The interaction of crystals with light depends both on the arrangement of atoms in their crystal structure and on the nature of these atoms. The optical properties of crystals indicate the directions of symmetry axes in the crystal and, in certain cases, provide useful preliminary information 

The vast majority of crystals are anisotropic, that is, their properties are not the same in all directions within the crystal. Light is said to be plane polarized (also called linearly polarized) when the electric field oscillates in a straight line. When, on the other hand, the electric field vector travels aronnd a circle, then the light is said to have circnlar polarization, and when the ends of the vector travel in an ellipse, it is said to be elliptically polarized. 

FIGURE 5.3. Refraction illustrated by (a) movements of car wheels and (b) passage of light into a different medium. 

If the angle of incidence of light is greater than a certain angle (the critical angle), the radiation may be reflected back into the incident medium, a phenomenon called total internal reflection. Internal re- 

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