Nicol prism.

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It is an optical device made from calcite crystal & is used in many optical instruments for producing & analysing plane polarized light. It derives its name from its inventor William Nicol who first designed it 1828.
It is based on the phenomenon of double refraction when an unpolarized light ray passes through a calcite crystal it splits into 2 refracted rays i.e o-ray & E-ray. The vibrations of E-ray are in the plane of paper while those of o-ray are perpendicular to plane of paper. Both these rays are plane polarized & are perpendicular to each other. For obtaining only single polarized beam, we should eliminate the other beam. Nicol prism is made in such a way that it eliminates o-ray by TIR & only E-ray comes out of the prism.

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