Presented in Figure 3 is an illustration of the construction of a typical Nicol prism. A crystal of
doubly refracting (birefringent) material, usually calcite, is cut along the plane labeled a-b-c-d
and the two halves are then cemented together to reproduce the original crystal shape. A beam of
unpolarized white light enters the crystal from the left and is split into two components that are
polarized in mutually perpendicular directions. One of these beams (labeled the ordinary ray) is
refracted to a greater degree and impacts the cemented boundary at an angle that results in its
total reflection out of the prism through the uppermost crystal face. The other beam
(extraordinary ray) is refracted to a lesser degree and passes through the prism to exit as a planepolarized beam of light.
Other prism configurations were suggested and constructed during the nineteenth and early
twentieth centuries, but are currently no longer utilized for producing polarized light in most
applications. Nicol prisms are very expensive and bulky, and have a very limited aperture, which
restricts their use at high magnifications. Instead, polarized light is now most commonly
produced by absorption of light having a set of specific vibration directions in a dichroic
medium. Certain natural minerals, such as tourmaline, possess this property, but synthetic films
invented by Dr. Edwin H. Land in 1932 soon overtook all other materials as the medium of
choice for production of plane-polarized light. Tiny crystallites of iodoquinine sulphate, oriented
in the same direction, are embedded in a transparent polymeric film to prevent migration and
reorientation of the crystals. Land developed sheets containing polarizing films that were
marketed under the trade name of Polaroid®, which has become the accepted generic term for
these sheets. Any device capable of selecting plane-polarized light from natural (unpolarized)
white light is now referred to as a polar or polarizer, a name first introduced in 1948 by A. F.
Hallimond. Today, polarizers are widely used in liquid crystal displays (LCDs), sunglasses,
photography, microscopy, and for a myriad of scientific and medical purposes.
Light exiting the port in the microscope base is first passed through a neutral linear Polaroid HNtype polarizer to create plane-polarized light having a vibration vector that is confined to a single
plane. H-films are produced by stretching a sheet of polyvinyl alcohol to align the long-chain
polymeric molecules, which are subsequently impregnated with iodine. These films are less
effective polarizing devices than a calcite prism, but do not restrict numerical aperture.
Typically, a pair of crossed polarizing H-films transmits between 0.01 percent and 40 percent of
the incident light, depending upon the film thickness.
Nicol Prisms
Discover how a Nicol prism can split a beam of white light into two component light rays that
have electronic vibration vectors that are mutually perpendicular.
Start Tutorial »
On most microscopes, the polarizer is located either on the light port or in a filter holder directly
beneath the condenser. The microscope illustrated in Figure 2 has a rotating polarizer assembly
that fits snugly onto the light port in the base. The polarizer can be rotated through a 360-degree
angle and locked into a single position by means of a small knurled locking screw, but is
generally oriented in an East-West direction by convention. Other microscopes typically have the
polarizer attached to the substage condenser assembly housing through a mount that may or may
not allow rotation of the polarizer. Some polarizers are held into place with a detent that allows
rotation in fixed increments of 45 degrees. Polarizers should be removable from the light path,
with a pivot or similar device, to allow maximum brightfield intensity when the microscope is
used in this mode.
Light diffracted, refracted, and transmitted by the specimen converges at the back focal
plane of the objective and is then directed to an intermediate tube (illustrated in Figure 4),
which houses another polarizer, often termed the "analyzer". The analyzer is another HNtype neutral linear Polaroid polarizing filter positioned with the direction of light
vibration oriented at a 90-degree angle with respect to the polarizer beneath the
condenser. By convention, the vibration direction of the polarizer is set to the East-West
(abbreviated E-W position), as illustrated in the birefringence interactive Java tutorial.
The same convention dictates that the analyzer is oriented with the vibration direction in
the North-South (abbreviated N-S) orientation, at a 90-degree angle to the vibration
direction of the polarizer.
Nicol prism
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A Nicol prism
A Nicol prism is a type of polarizer, an optical device used to produce a polarized beam of light
from an unpolarized beam. It is made in such a way that it eliminate one of the ray by Total
Internal Reflection i.e, O-ray is eliminated and only E-ray is transmitted through the prism.See
polarized light. It was the first type of polarizing prism to be invented, in 1828 by William Nicol
(1770–1851) of Edinburgh. It consists of a rhombohedral crystal of Iceland spar (a variety of
calcite) that has been cut at an angle of 68° with respect to the crystal axis, cut again diagonally,
and then rejoined as shown using, as a glue, a layer of transparent Canada balsam.
Unpolarized light enters through the left face of the crystal, as shown in the diagram, and is split
into two orthogonally polarized, differently directed, rays by the birefringence property of the
calcite. One of these rays (the ordinary or o-ray) experiences a refractive index of no = 1.658 in
the calcite and it undergoes total internal reflection at the calcite-glue interface because its angle
of incidence at the glue layer (refractive index n = 1.55) exceeds the critical angle for the
interface. It passes out the top side of the upper half of the prism with some refraction as shown.
The other ray (the extraordinary ray or e-ray) experiences a lower refractive index (ne = 1.486)
in the calcite, and is not totally reflected at the interface because it strikes the interface at a subcritical angle. The e-ray merely undergoes a slight refraction, or bending, as it passes through the
interface into the lower half of the prism. It finally leaves the prism as a ray of plane polarized
light, undergoing another refraction as it exits the far right side of the prism. The two exiting rays
have polarizations orthogonal (at right angles) to each other, but the lower, or e-ray, is the more
commonly used for further experimentation because it is again traveling in the original
horizontal direction, assuming that the calcite prism angles have been properly cut. The direction
of the upper ray, or o-ray, is quite different from its original direction because it alone suffers
total internal reflection at the glue interface as well as a final refraction on exit from the upper
side of the prism.
Nicol prisms were once widely used in microscopy and polarimetry, and the term "using crossed
Nicols" (abbreviated as XN) is still used to refer to the observing of a sample placed between
orthogonally oriented polarizers. In most instruments, however, Nicol prisms have been replaced
by other types of polarizers such as Polaroid sheets and Glan–Thompson prisms.
[edit]
Nicol Prism
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.
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.
Polarizing prisms
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.
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.
Unpolarised light incidence
When a ray SM of unpolarised light parallel to the face AD’ is incident on the face AB’ of the prism, it
splits up into two refracted rays, the ordinary ray and the extra ordinary. Both of the O and E ray are
plane polarized the vibrations of O ray being perpendicular to the principal section of the crystal; while
that of E ray being in the principal section. The ordinary ray in going from calcite to Canada Balsam
travels from optically denser medium to a rarer medium.
As the length of calcite crystal is large, the angle of incidence at Calcite – Balsam surface for the
ordinary ray is greater than the critical angle. Therefore when O ray is incident on Calcite –
Balsam surfaces it is totally reflected and is finally absorbed by the side AD’ which is blackened.
The extra ordinary ray travels from an optically rare medium to a denser medium, therefore it is
not affected by the Calcite – Balsam surface and it is therefore transmitted through the prism.
This “E ray is plane polarized and had vibration, in the principal section parallel to the shorter
diagonal of the end face of the crystal. Thus by Nicol prism we are able to get a single beam of
place polarized light. Thus Nicol prism can be used as a polarizer.
Limitations
When the angle of incidence at the crystal surface is increased, the angle of incidence at Calcite –
Balsam surface decreases. When the angle S0MS becomes greater than 14o, the angle of incidence of
Calcite – Balsam surface becomes less than the critical angle. In this position ordinary ray is also
transmitted through the prism along with extraordinary ray so light emerging from Nicol prism will not
be plane polarized.
When angle of incidence at crystal surface is decreased, the extraordinary ray makes less angle
with the optic axis, as a result its refractive index increase, because the refractive index of calcite
crystal for E ray is different in different directions through the crystal being maximum when the
E ray travels at right angles to the optic axis and minimum when E ray travels along with O ray
and no light emerges from the prism
Nicol prism as analyzer
Consider two Nicol prisms arranged coaxially one after another. When a beam of unpolarized light is
incident on the first prism P, the emergent beam is plane polarized with its vibrations in principal section
of first prism. This prism is called polarizer. When principal section of both prisms are parallel then
intensity of emergent light is maximum. But when the principal sections are at right angles to each other
the, intensity of emergent light is minimum i.e., there no light it transmitted through the second prism.
Here first prism produced plane polarized light and 2nd prism detects and analyses it.
Nicol Prisms
Several versions of prism-based polarizing devices were once widely available, and these were usually
named after their designers. The most common polarizing prism (illustrated in the tutorial window) was
named after William Nicol, who first cleaved and cemented together two crystals of Iceland spar with
Canada balsam in 1829. Nicol prisms were first used to measure the polarization angle of birefringent
compounds, leading to new developments in the understanding of interaction between polarized light and
crystalline substances. This interactive tutorial explores the generation of orthogonal or mutually
perpendicular (ordinary and extraordinary) waves as the result of light transmission through a Nicol
prism.
A typical Nicol prism is composed of a doubly refracting (birefringent) material, usually calcite, cut along
the plane labeled a-b-c-d, as illustrated in the tutorial window. The two halves are then cemented
together to reproduce the original crystal shape. A beam of unpolarized white light enters the crystal from
the left and is split into two components that are polarized in orthogonal directions. One of these beams
(labeled the ordinary ray) is refracted to a greater degree and impacts the cemented boundary at an
angle that results in its total reflection out of the prism through the uppermost crystal face. The other
beam (extraordinary ray) is refracted to a lesser degree and passes through the prism to exit as a planepolarized beam of light. To operate the tutorial use the radio buttons labeled White Light and
Monochromatic Light to toggle between these two illumination modes. When the tutorial is placed in
monochromatic light mode, the Wavelength slider is activated, and can be utilized to alter the incident
light wavelength in the range of 400 to 700 nanometers.
Polarized light microscopy was first introduced during the nineteenth century, but instead of employing
transmission-polarizing materials, light was polarized by reflection from a stack of glass plates set at a 57degree angle to the plane of incidence. Later, more advanced instruments relied on a crystal of doubly
refracting material (such as calcite) specially cut and cemented together to form a prism. A beam of white
unpolarized light entering a crystal of this type is separated into two components that are polarized in
mutually perpendicular directions. One of these light rays is termed the ordinary ray, while the other is
called the extraordinary ray. The ordinary ray is refracted to a greater degree in the birefringent crystal
and impacts the cemented surface at the angle of total internal reflection. As a result, this ray is reflected
out of the prism and eliminated by absorption in the optical mount. The extraordinary ray traverses the
prism and emerges as a beam of linearly polarized light that is passed through the substage condenser
directly to the specimen (positioned on the microscope stage).
Other prism configurations were suggested and constructed during the nineteenth and early twentieth
centuries, but are no longer utilized for producing polarized light in most applications. Nicol prisms are
very expensive and bulky, and have a very limited aperture, which restricts their use at high
magnifications. Instead, polarized light is now most commonly produced by absorption of light having a
set of specific vibration directions in a dichroic medium. Certain natural minerals, such as tourmaline,
possess this property, but synthetic films invented by Dr. Edwin H. Land in 1932 soon overtook all other
materials as the medium of choice for production of plane-polarized light. Tiny crystallites of iodoquinine
sulfate, oriented in the same direction, are embedded in a transparent polymeric film to prevent migration
and reorientation of the crystals. Land developed sheets containing polarizing films that were marketed
under the trade name of Polaroid (a registered trademark), which has become the accepted generic term
for these sheets. Any device capable of selecting plane-polarized light from natural (unpolarized) white
light is now referred to as a polar or polarizer, a name first introduced in 1948 by A. F. Hallimond. Today,
polarizers are widely used in liquid crystal displays (LCDs), sunglasses, photography, microscopy, and for
a myriad of scientific and medical purposes.
Definition of NICOL PRISM
: a device used for the production or analysis of polarized light consisting of the two parts of a
rhombohedron of clear calcite bisected obliquely at a particular angle and subsequently cemented
together with a transparent cement of which the refractive index lies between that of calcite for the
ordinary ray which is totally reflected at the cement interface and the maximum refractive index of
calcite for the extraordinary ray which is alone transmitted, both rays being plane-polarized at right
angles to each other
Variants of NICOL PRISM
Nic·ol prism also Nicol
Origin of NICOL PRISM
after William Nicol †1851 Brit. physicist who invented itHe started out as aide to his uncle,
Henry Moyes, an itinerent lecturer in Natural Philosophy whose blindness necessitated assistance
for his chemistry and optics demonstrations.[1][2] Nicol, having himself become a popular lecturer
on that subject at the University of Edinburgh, settled in Edinburgh to live a very retired life. He
conducted extensive studies of fluid inclusions in crystals and the microscopic structure of fossil
wood.[3] He did not publish any of his research findings until 1826.
Nicol made his prism by bisecting a parallelepiped of Iceland spar (a naturally occurring,
transparent crystalline form of calcium carbonate) along its shortest diagonal, then cementing the
two halves together with Canada balsam. Light entering the prism is refracted into two rays, one
of which emerges as plane-polarized light. Nicol prisms greatly facilitated the study of refraction
and polarization, and were later used to investigate molecular structures and optical activity of
organic compounds.
In 1815, Nicol developed a method of preparing extremely thin sections of crystals and rocks for
microscopical study. His technique (which involved cementing the specimen to a glass slide and
then carefully grinding until it was extremely thin) made it possible to view mineral samples by
transmitted rather than reflected light and therefore enabled the minerals' internal structures to be
seen.
He died at Edinburgh on the 2 September 1851, and was buried in Warriston Cemetery. His
burial site is now marked by a plaque on the north wall.
Dorsum Nicol on the Moon is named after him.
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