Dubbelbrytning

Dubbelbrytning, also known as birefringence, is an optical property in certain materials where the refractive index depends on the polarization and propagation direction of light. This means that light entering such a material can split into two distinct rays, each traveling at a different speed and along a slightly different path. These two rays are known as the ordinary ray (o-ray) and the extraordinary ray (e-ray).

The ordinary ray travels with a refractive index that is independent of its direction within the crystal. The extraordinary ray, however, experiences a refractive index that varies with its direction relative to the crystal's optical axis. This difference in refractive indices causes the two rays to refract at different angles when they pass through the material at an oblique angle. This phenomenon is a consequence of the anisotropic nature of the crystal structure, where the arrangement of atoms or molecules leads to different optical properties in different directions.

Materials exhibiting dubbelbrytning include calcite, quartz, and many artificially produced crystals and polymers. The effect is most pronounced when light enters the material perpendicular to the optical axis. Dubbelbrytning has practical applications in various optical devices, such as polarizers, waveplates, and optical modulators, which are used in scientific instruments, cameras, and liquid crystal displays. Observing the colors produced when plane-polarized light passes through a birefringent material between crossed polarizers is a common demonstration of this phenomenon.