POLARIZATION
AND
HUYGEN’S THEORY
OF DOUBLE
REFRACTION
Anuroop Ashok
Ist Yr. B Tech
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POLARIZATION OF LIGHT - BIREFRINGENCE AND CRYSTALS, Slides of Electromagnetism and Electromagnetic Fields Theory
Slides on Polarization and Birefringence.
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AND
HUYGEN’S THEORY
OF DOUBLE
REFRACTION
Anuroop Ashok
Ist Yr. B Tech
HISTORICAL CONTEXT
Before the beginning of the nineteenth century, light was
considered to be a stream of particles.
The particles were either emitted by the object being
viewed or emanated from the eyes of the viewer.
Newton was the chief architect of the particle theory of
light.
- He believed the particles left the object and stimulated the
sense of sight upon entering the eyes
NATURE OF LIGHT
The optical phenomena like interference and
diffraction exhibited by the light establishes its wave
nature.
The nature of this wave is given by the phenomena of
Polarization.
Light is an ElectroMagnetic Wave and Polarization
proves Light to be a transverse Wave.
Thus Light has an Electric vector (E) and a Magnetic
vector(M) vibrating in perpendicular directions.
Electric field vector is of primary imporatance.
Lights are Electromagnetic Waves
There are three type of polarized
light
Plane Polarized Light (ppl or lpl)
Circularly
Polarized Light (cpl)
- Elliptically Polarized Light (epl)
PRODUCTION OF PLANE
POLARIZED LIGHT
- By Reflection
- By Refraction
- By Selective Absorption( Dichroizm )
- By Scattering
- By Double Reflection
DOUBLE REFRACTION OR
BIREFRINGENCE
When ordinary light is allowed to pass through a calcite
or quartz , it splits into two refracted beams(O-ray &E –
ray )and both are plane polarized lights.
. HUYGEN’S PRINCIPLE
**Huygens’ principle,** in optics, a statement that all points of a wave front of light in a vacuum or transparent medium may be regarded as new sources of
wavelets that expand in every direction at a rate depending on their velocities.
- “ Every point on a wave-front may be considered a source of secondary
spherical wavelets which spread out in the forward direction at the speed of
light. The new wave-front is the tangential surface to all of these secondary
wavelets.”
- Proposed by the Dutch mathematician, physicist, and astronomer ,Christiaan
Huygens, in 1690, it is a powerful method for studying various optical
phenomena.
A surface tangent to the wavelets constitutes
the new wave front and is called the envelope of the wavelets. If a medium is
homogeneous and has the same properties throughout ( i.e., is isotropic),
permitting light to travel with the same speed regardless of its direction of
propagation, the three-dimensional envelope of a point source will be
spherical; otherwise, as is the case with many crystals, the envelope will be
ellipsoidal in shape ( see double refraction). An extended light source will
consist of an infinite number of point sources and may be thought of as
generating a plane wave front.
A wavefront is a surface over which an optical wave
has a constant phase. For example, a wavefront could
be the surface over which the wave has a maximum
(the crest of a water wave, for example) or a minimum
(the trough of the same wave) value. The shape of a
wavefront is usually determined by the geometry of the
source. A point source has wavefronts that are spheres
whose centers are at the point source.
WAVE SURFACES FOR
NEGATIVE AND
POSITIVE CRYSTALS
NEGATIVE CRYSTALS
- Negative crystals are crystals in which refractive index
corresponding to E-Ray (n
E ) is less than the refractive index corresponding to O-Ray ( nO ) in
all directions except for Optic axis.
The E-Ray travels faster than O-Ray except along the Optic axis.
The spherical O-Wavefront is entirely within the ellipsoidal E -Wavefront.
Ex: Calcite , Tourmaline ,Ruby ...
POSITIVE CRYSTALS
- Positive crystals are crystals in which refractive for O-Ray is less than
that for E-Ray(n
O<nE ).
The velocity of O-Ray is greater than or equal to the velocity of E-Ray.
The ellipsoidal E-wavefront is entirely within the spherical O-wavefront .
Example : Quartz (SiO2) ,
Sellaite (MgF2),Rutile (TiO2),…