Keywords:polarised, nicol, analyser, rhombohedron
This article is about Nicol prism, an optical device used to produce plane polarised light.
Nicol prism is an optical device designed from calcite and is used for the production and analysis of plane polarised light. A beam of ordinary light entering the calcite crystal breaks up into E-rays (Extraordinary rays) and O-rays (Ordinary rays) by double refraction. The O-ray is cut off by total internal reflection while the E-ray is allowed to pass through.
To construct a Nicol prism a calcite rhombohedron of length three times its breadth is produced from natural crystal by cleavage. The end faces are then cut artificially so that the acute angles of the principal section is reduced from 71° to 68°. The resulting crystal is then cut into two portions by a plane perpendicular to both the principal section and the end faces of the rhombohedron. The cut surfaces are highly polished and cemented together by a layer of Canada-balsam. The sides of the prism are coated with lamp-black and is kept covered by a brass tube. The two end faces are kept open so that the light incident on one end face may come out emerging from the other face in the end.
A section of the resulting crystal parallel to the principal section is shown below:
A text book on light — B Ghosh , K.G.Mazumdar