ENGINEERING PHYSICS

K L University

ByG.SUNITA

DEPARTMENT OF PHYSICS

Polarisation Lecture 4

3NareN @ KLU

Significance of optical Axis

Polarization…

Velocities of O-ray and e-ray:

Polarization…

http://www.microscopyu.com/print/articles/polarized/birefringence-print.html

Negative Crystal:

Polarization…

E-ray wavefront travels faster than O-ray wave front

Velocity of E-ray > Velocity of O-ray

Crystals Like Calcite and Tourmaline

http://www.microscopyu.com/print/articles/polarized/birefringence-print.html

Positive Crystal:

Polarization…

O-ray wavefront travels faster than E-ray wave front

Velocity of O-ray > Velocity of E-ray

Crystals Like Ice and Quartz

Polarization…Wave Plate:

A waveplate or retarder is an optical device that alters the polarization state of a light wave travelling through it.

Wave plate

Quarter wave plate Half wave plate

Polarization…Quarter Wave Plate: It produces the phase difference “п/2” or path difference “λ/4”

• Calcite crystal cut with optic axis parallel to the surface.

http://www.learnerstv.com/animation/animation.php?ani=90&cat=physicshttp://www.edumedia-share.com/media.php?id=970

Polarization…Quarter Wave Plate: It produces the phase difference “п/2” or path difference “λ/4”

http://www.learnerstv.com/animation/animation.php?ani=90&cat=physicshttp://www.edumedia-share.com/media.php?id=970

Polarization…

It produces the phase difference “п” or path difference “λ/2”

HWP produces a phase difference п between O-ray and e-ray.

Emergent beam from a HWP is plane polarized light.

Half Wave Plate:

http://demonstrations.wolfram.com/PolarizationOfAnOpticalWaveThroughPolarizersAndWavePlates/

Circularly and Elliptically Polarized Light:

Polarization…

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Polarization…Circularly and Elliptically Polarized Light:

Polarization…

Effect of Nicol’s Prism on different

polarized lights

Polarization…

No change in IntensityUPL

PartiallyPL Imax(2)

Imin(2) ≠ 0

Polarization…

PPL Imax(2)Imin(2) = 0

CPLNo change in Intensity

Polarization…

EPLImax(2)Imin(2) ≠ 0

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Polarization…Input Nicol Prism output

UN POLARISED LIGHTRotated by 360o

No change in Intensity

PARTIALLY POLARISED LIGHT Rotated by 360o

Intensity Max (2) Intensity Min(2) not equal to zero

PLANE POLARISED LIGHT Rotated by 360o

Intensity Max (2) Intensity Min(2) equal to zero

CIRCULLARLY POLARISED LIGHT

Rotated by 360o No change in Intensity

ELLIPTICALLY POLARISED LIGHT Rotated by 360o

Intensity Max (2) Intensity Min(2) not equal to zero

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Polarization…

Effect of Quarter Wave Plate on Different Polarized Lights

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Polarization…

UPL UPL

CPL PPL

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Polarization…

EPL PPL

Partially PL Partially PL

Polarization…

PPL

PPL 0O, 180O

CPL 45O, 135O ,225O, 315O

EPL At any Angle’sExcept the above

Polarization…Input Quarter wave plate output

UN POLARISED LIGHT Quarter wave plate UN POLARISED LIGHT

CIRCULLARLY POLARISED LIGHT Quarter wave plate PLANE POLARISED LIGHT

ELLIPTICALLY POLARISED LIGHT Quarter wave plate PLANE POLARISED LIGHT

PARTIALLY POLARISED LIGHT Quarter wave plate PARTIALLY POLARISED

LIGHT

PLANE POLARISED LIGHT Quarter wave plate(rotated from 0o to 360o)

PPL (0o, 180o)CPL (45o, 135o, 225o, 315o)

EPL (Any angle)

Polarization…

Polarization…

Polarization…Problems:

1.Plane polarized light is incident on a piece of quarter cut parallel to the axis. Find the least thickness for which the ordinary and e- ordinary combine to form plane polarized light. Given

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Polarization…

Polarization…

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Polarization…

Production of Polarized Light by different methods:

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Polarization…

Polarized light by Reflection:

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Polarization…

. . .. .. ..

. . . . .. ..

X Y

N

N1

P

O

Q

R

Polarization by Reflection

I =

p

r = p

r

.N1R

.. .http://www.launc.tased.edu.au/online/sciences/physics/Polari.htm

Polarization…Polarization by ReflectionBrewster’s law- That the tangent angle of polarization (p) is numerically equal to the refractive index(µ) of the medium.

Polarization…Polarization by reflection:

• a) horizontally• b) vertically

horizontalverticaldirection of polarizationof reflected light

Polarization…Polarization by Reflection:

wearing sunglasses will help reducing glare (reflection) from flat surfaces (highway/water)

without with sunglasses

Polarization…Polarization by Transmission:

Pile of platesPolarizing angle for glass: 57.5 Inclined at 32.5

Transmitted light is partially polarized

Polarization…Polarization by Transmission:

Purely plane polarized

DOUBLE REFRACTION

Polarization…

Polarization…Geometry of Calcite Crystal :

• Known as Iceland spar.• It is colourless crystal.• It is transparent to ultraviolet and visible light.• It belongs to rhombohedral class

of hexagonal system.• Calcium carbonate (CaCO3).• The six faces are parallelograms

each having angles 101o 55’ and 78o 5.

Polarization…

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Calcite Crystal :

CaCO3

Blunt CornerOptic axisPrinciple sectionUniaxial crystalsBiaxial crystals

NareN @ KLU

Optic axis :

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• An imaginary line passing through one of the blunt corners and making equal angles with all the three faces is called optic axis.

• Optic axis is not an imaginary line but it is a direction.

• Any line parallel to optic axis also acts as optic axis.

Polarization…

Polarization…Principle Section:

A Plane which contains the optic axis and is perpendicular to two opposite faces is called a principle section.

Crystal having one optic axis are called uniaxial crystal. Eg: quartz and calcite.

Crystal having two optics axis are called biaxial crystal. Eg: mica.

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Double Refraction : (Birefringence)

Experiment

Polarization…

Anisotropic substance : physical prop. are different

Polarization…

• O E

http://www.science.smith.edu/geosciences/min_jb/Optics/Optics-3.pdf

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Double Refraction : (Birefringence)

Polarization…

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Double Refraction : (Birefringence)Polarization…

Refractive indices:

In case of calcite:

When both rays are travel with same velocity along optic axis.

Significance of optical Axis

Polarization…NICOL’S PRISM:

1.Principle 2.Construction3.Action4.Limitations5.Uses

Calcite

canada balsam

O ray

E ray

Principle :Optical Device.Double RefractionTransmit extra-ordinary ray and cut off

ordinary rayConstruction:• Length is 3 times as its width• End Faces grounded – 68 and 112 instead of 71 and 109• Cut into two pieces – grounded – polished – cemented (With Canada balsam) .

Polarization…

Polarization…

µₒ = 1.658 µe = 1.486 µcanada balsam = 1.55

Polarization…

Action: Light entered the faces

Canada balsam acts asRarer medium for O-rayDenser medium for E-ray

E-ray:Straight linePlane polarized

O-ray:Total internal reflection> critical angle

Polarization…

Limitations:

1. Much smaller than the ∠ SMB with face AB – O-ray strikes less than Өc

Both O-ray and E-rays transmittedAngle of incidence : 14 ◦

2. Angle grater than SMB with face AB -- E-ray will ∠refract

suffer total reflection --- No light

To obtain plane polarized light, the incident beam should be confined with an angle of 14 on either side of SM

Polarization…Uses:

Polarizer

Analyzer

Polarization…

1. A Ray of light is incident on the surface of glass plate µ=1.56 at the polarizing angle. Calculate the angle of refraction.

2. Calculate the Brewster angle for the following liquids Ethyl alcohol , µ=1.361Carbon tetrachloride µ=1.461

3. The velocity of light in water is 2.2*108 m/s. What is the polarizing angle of incidence foe water surface? (c=3.8*108 m/s)

http://demonstrations.wolfram.com/PolarizationOfAnOpticalWaveThroughPolarizersAndWavePlates/

Polarization…• Types of polarized lights• Detection and production of PPL• Production of CPL &EPL• Nicol’s prism