What is "birefringence"

n. (context physics English) the splitting of a ray of light into two parallel rays of perpendicular polarization by passage through an optically anisotropic medium

n. splitting a ray into two parallel rays polarized perpendicularly [syn: double refraction]

Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefringence is often quantified as the maximum difference between refractive indices exhibited by the material. Crystals with non-cubic crystal structures are often birefringent, as are plastics under mechanical stress.

Birefringence is responsible for the phenomenon of double refraction whereby a ray of light, when incident upon a birefringent material, is split by polarization into two rays taking slightly different paths. This effect was first described by the Danish scientist Rasmus Bartholin in 1669, who observed itSee:

• Erasmus Bartholin, Experimenta crystalli islandici disdiaclastici quibus mira & infolita refractio detegitur [Experiments on birefringent Icelandic crystal through which is detected a remarkable and unique refraction] (Copenhagen, Denmark: Daniel Paulli, 1669).
• Erasmus Bartholin (January 1, 1670) "An account of sundry experiments made and communicated by that learn'd mathematician, Dr. Erasmus Bartholin, upon a chrystal-like body, sent to him out of Island," Philosophical Transactions of the Royal Society of London, 5 : 2041-2048. in calcite, a crystal having one of the strongest birefringences. However it was not until the 19th century that Augustin-Jean Fresnel described the phenomenon in terms of polarization, understanding light as a wave with field components in transverse polarizations (perpendicular to the direction of the wave vector).