The document discusses polarization and double refraction of light passing through anisotropic crystals like calcite. It explains that when light passes through such crystals, it is split into two rays that are plane polarized with mutually perpendicular planes of polarization. These two rays are called the ordinary ray (O-ray) and extraordinary ray (E-ray). The O-ray follows Snell's law of refraction, while the E-ray violates it, though its wave normal still follows Snell's law. This phenomenon of double refraction was first reported when light passed through calcite crystals.

1. POLARIZATION BY
DOUBLE REFRACTION
Peer Team
Santhoshkumar. R
Suryaa. E

2. Refraction
Refraction is the redirection of a wave as it passes from one medium to another.
The redirection can be caused by the wave's change in speed or by a change in
the medium. Refraction of light is the most commonly observed phenomenon, but
other waves such as sound waves and water waves also experience refraction.
How much a wave is refracted is determined by the change in wave speed and the
initial direction of wave propagation relative to the direction of change in speed.

3. Polarization
Polarisation of light waves is the phenomenon of restricting
the plane of vibration of electric field vector of light in a
definite plane.

4. Types of polarized light
• Plane polarized light
• Circularly polarized light
• Elliptically polarized light

5. Double refraction
Light passing through a calcite crystal is split into two rays. This process, first
reported by Erasmus Bartholinus in 1669, is called double refraction. The two rays
of light are each plane polarized by the calcite such that the planes of
polarization are mutually perpendicular. For normal incidence (a Snell’s law angle
of 0°), the two planes of polarization are also perpendicular to the plane of
incidence.

6. O-ray and E-ray
■ For normal incidence (a 0° angle of incidence), Snell’s law predicts that
the angle of refraction will be 0°. In the case of double refraction of a
normally incident ray of light, at least one of the two rays must violate
Snell’s Law as we know it. For calcite, one of the two rays does indeed
obey Snell’s Law; this ray is called the ordinary ray . The other ray is an
extraordinary ray.
■ For ordinary rays the vibration direction, indicated by the electric vectors
in our illustrations, is perpendicular to the ray path. For extraordinary
rays, the vibration direction is not perpendicular to the ray path. The
direction perpendicular to the vibration direction is called the wave
normal. Although Snell’s Law is not satisfied by the ray path for
extraordinary rays, it is satisfied by the wave normal of extraordinary rays.
In other words, the wave normal direction for the refracted ray is related

7. O-ray and E-ray

8. Types of crystal
■ ISOTROPIC CRYSTAL
ex: Glass, Table salt
■ ANISTRIOPIC CRYSTAL
ex: Quartz , Calcite and Tourmaline

9. Huygen's principle
■ While the Huygens' principle of double refraction explains the phenomenon of
double refraction in an optically anisotropic medium, the Huygens–Fresnel
principle pertains to the propagation of waves in an optically isotropic medium.
According to the Huygens–Fresnel principle, each point on a wavefront can be
considered a secondary point source of waves, so a new wavefront is formed
after the secondary wavelets have travelled for a period equal to one vibration
cycle. This new wavefront can be described as an envelope or tangent surface
to these secondary wavelets. Understanding and forecasting the classical wave
propagation of light is based on the Huygens-Fresnel principle.

10. Huygen's principle

11. “When you talk, you are only
repeating what you already know.
But if you listen, you may learn
something new”
-Dalai lama