Nicol Prism

NICOL, Nicol prism, a ^gpolarizing prism, invented by the English physicist Nicol (William Nicol, 1768-1851). The Nicol prism is an essential part of polarization apparatus: polarizing microscope, polarimeter, some photometers, etc., in which there are "nicol" polarizers and analyzers. The Nicol prism is made from Iceland spar (CaCO₃), which has very strong double refraction. Due to its special design, one of the resulting rays ("ordinary") is removed, and the other ("extraordinary") emerges from the nicol as a plane-polarized ray. The diagram of this prism was first published in the "Edinburgh new philosophical journal" (v. VI, p. 83, 1828). At present, there are also other designs of such prisms, for example the Thomson prism, Ahrens prism, etc. (see figure).