Question: Describe the construction and working method of nicol prism??

by Jaya
March 14, 2021

Answers
Vipin Kumar March 14, 2021
Nicol Prism

Nicol prism is an optical device which is used for producing and analyzing plane polarized light in practice.

The Nicol prism is made up from two prisms of calcite cemented with Canada balsam. The ordinary ray can be caused to totally reflect off the prism boundary, leaving only the extraordinary ray.

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Nicol Prism is based upon phenomenon of Double refraction. It is constructed from the calcite crystal PQRS having length three times of its width. The crystal is then cut diagonally into two parts.

Polarization can be achieved with crystalline materials which have a different index of refraction in different crystal planes. Such materials are said to be birefringent or doubly refracting.

Basic Principle
The basic principle behind Nicol Prism is based on its unique behaviour on the event of incidence of light rays on its surface.
When an ordinary ray of light is passed through a calcite crystal, it is broken up into two rays:

An ‘Ordinary ray’ which is polarized and has its vibrations perpendicular to the principle section of the crystal and
An extra-ordinary ray which is polarized and whose vibration is parallel to the principle section of the prism.If by some optical means, one of the two rays eliminates, the ray emerging through the crystal will be Plane polarized. In Nicol Prism, ordinary ray is eliminated and Extra-ordinary ray, which is plane polarized, is transmitted through the prism.

Construction
A calcite crystal’s length is three times its breadth. Let ADFGBC be such a crystal having ABCD as a principle section of the crystal with BAD = 700.

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The end faces of the crystal are cut in such a way that they make angles of 680 and 1120 in the principle section instead of 710 and 1090. The crystal is then cut into two pieces from one blunt corner to the other along two pieces from one blunt corner to the other along a plane perpendicular to the extra ordinary rays.
  1. Refractive index of Calcite for O ray,
  2. Refractive index of Canada balsam,
  3. Refractive index Calcite of E ray,
Thus we see that the Canada Balsam is optically denser than calcite for E ray and rarer for O ray. Finally the crystal is enclosed in a tube blackened inside.
Vasu Chitteti March 14, 2021

Nicole Prism:
It is an optical device which is used for producing & Analyzing Plane polarized light.

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Working Principle: Nicole Prism works on the Huygens' Theory of Double Refraction
It describes:
• When a light wave strikes the surface of a doubly refracting crystal, It splits the wave into Two wavelets.
Ordinary ray and
Extraordinary ray

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 • These two wavelets spread out into the crystal.
• The wavefront corresponding to O- ray is spherical as the velocity of O-ray remains the same in all the directions.
• The wave front corresponding to E- ray is an ellipsoid of revolution with the optic axis as its axis of revolution. This is due to the fact that the velocity of E-ray is different in different directions in the crystal.
• The two wave fronts corresponding to O-ray and E-ray touch each other along the optic axis since both the rays travel with
the same velocity along the direction of optic axis.
• For Negative uniaxial crystals (like calcite) in which the velocity of O-ray is less than the velocity of E-ray, sphere lies inside the ellipsoid.
• However, for Positive uniaxial crystals
(like quartz) the ellipsoid lies inside the sphere since in this case the velocity of O-ray is greater than the velocity of E-ray.

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Construction:
It is constructed from the Calcite crystal having length three times of its width.
• Its face angles are 68° and 112°. 

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 • The crystal is then cut diagonally into two parts. The surfaces of these parts are
grinded to make optically flat and then these are polished.

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 • Thus polished surfaces are connected together with a special cement known as
Canada Balsam.

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Working:
• When a beam of unpolarised light is incident on the face, it gets split into two refracted rays, named O-ray and E-ray.

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 • These two rays are plane polarised rays, whose vibrations are at right angles to
each other.
• The refractive index of Canada balsam cement being 1.55 lies between those of ordinary and extraordinary and 1.4864, respectively.
• So, It is clear that Canada Balsam layer acts as an optically Rarer medium for the ordinary ray and it acts as an Optically denser medium for the extraordinary ray.
• When ordinary ray of light travels in the calcite crystal and enters the Canada balsam cement layer, it passes from denser to rarer medium.
• Moreover, the angle of incidence is greater than the critical angle, the incident ray is totally internally reflected from the crystal and only extraordinary ray is transmitted
through the prism.
• Therefore, fully plane polarised wave is generated with the help of Nicol prism.

In order to produce and analyse the plane polarised light, we arrange two nicol prisms.