March 14, 2021
It is an optical device which is used for producing & Analyzing Plane polarized light.
Working Principle: Nicole Prism works on the Huygens' Theory of Double Refraction
• When a light wave strikes the surface of a doubly refracting crystal, It splits the wave into Two wavelets.
Ordinary ray and
• 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.
It is constructed from the Calcite crystal having length three times of its width.
• Its face angles are 68° and 112°.
• 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.
• Thus polished surfaces are connected together with a special cement known as
• When a beam of unpolarised light is incident on the face, it gets split into two refracted rays, named O-ray and E-ray.
• These two rays are plane polarised rays, whose vibrations are at right angles to
• 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.