Nicol's prism

Beam path in the Nicolian prism. The optical axis (OA) of the calcite prisms lies in the plane of the drawing. The vertical arrows superimposed on the extraordinary ray indicate the polarization direction parallel to the OA, the points on the ordinary ray the polarization perpendicular to it.

A Nicolian prism (after William Nicol , 1828) is a polarization prism that is glued together from two birefringent prisms .

The prisms usually consist of calcite . They are assembled into a parallelepiped in such a way that the optical axis of the crystal is parallel to the cut surface. The refractive index of the adhesive lies between the values for calcite. Traditionally, the glue used was Canada balsam , which has a refractive index of ; synthetic adhesives are common today. ${\ displaystyle n = 1 {,} 54}$

The angle of the interface to the beam path is chosen so that the proper beam experiences total reflection at the boundary between calcite and adhesive . The extraordinary jet, on the other hand, passes largely through the boundary layers between calcite and glue.

As a result, the two exiting light rays are polarized perpendicular to each other :

the ordinary beam is polarized perpendicular to the optical axis (TE polarized),
the extraordinary ray that emerges from the second calcite is polarized parallel to the optical axis (TM-polarized).

Nicol prisms were long time in the polarization microscopy as a polarizer used. They have now been replaced by polarizing films , which are cheaper and take up less space.

Individual evidence

↑ W. Nicol: On a method of so far increasing the divergence of the two rays in calcareous-spar that only one image may be seen at a time . In: Edinburgh New Philosophical Journal . tape 6 , 1828, pp. 83-94 .

[1] W. Nicol: On a method of so far increasing the divergence of the two rays in calcareous-spar that only one image may be seen at a time . In: Edinburgh New Philosophical Journal . tape 6 , 1828, pp. 83-94 .