Nicol Prism 1

Nicol Prism

When an ordinary ray of light is passed through a calcite crystal, it is broken up into two rays:
The ordinary ray which is polarized and has its vibrations perpendicular to the principle section of the crystal and then extra ordinary ray which is polarized and its vibration parallel to the principle section. If by some optical means one of the two rays eliminated the ray emerging through the crystal will be plane polarized. In Nicol Prism ordinary ray is eliminated extra ordinary ray, which is plane polarized, is transmitted through the prism.

March 17, 200938341 https://chemistrylearning.com/nicol-prism/