ABSTRACT
In many crystals applying an electric field alters the dielectric constant and the refractive index of the crystalline material. The forms of the components for the electro-optic tensor will depend on the definition of the mirror planes. The linear effect will not occur in centrosymmetric crystals; so although the quadratic effect can be expected to be small when both effects are present, it may be important in centrosymmetric crystals where the linear effect is absent. The rhombohedral cell contains two molecules whereas the hexagonal cell contains six and is the easier cell to use. Using crossed linear polarisers at the input and output stages, the light can be amplitude modulated, with zero output when no electric field is applied, and maximum output when the electric field is of the correct magnitude to rotate the polarised beam by 90°.
