Polarization of light and its application

1. Polarization and its application
PABITA DHUNGEL
B.OPTOMETRY
Institute of Medicine
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2. PRESENATION LAYOUT
• Introduction
• Types of polarized light
• Few related terms
• Few laws related to polarization
• Applications
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3. Introduction
• Light is form of energy which gives us the
sensation of vision
• Different properties of light are:
• Reflection
• Refraction
• Interference
• Diffraction
• Polarization
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4. What is polarization?
• The vibrations are limited to just one direction
in a plane perpendicular to the direction of
propagation, the wave is said to be plane
polarized
• Thus, the phenomenon of the restriction of
the vibration to a particular direction is called
polarization
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5. Contd…
• Unpolarized/ natural wave
Wave nature vibrating in all direction
Mixture of various plane polarized beam
e.g. sun, thermal, gaseous discharge lamp,
flame,etc
• polarized beam
Contains vibration in only one plane
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6. • Partial polarized light
Mixture of polarized and non polarized light
• The plane which contains the vibrations of
polarized light is called plane of vibration
• The plane normal to the plane of vibration is
called the plane of polarization
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7. Mathematically
• If direction of propagation is z, E field oscillates in
x direction, B field in y then:
Ex = E0 cos(ωt – 2πz/λ + δ)
By = B0 cos(ωt – 2πz/λ + δ)
E0,B0= amplitude of waves (related by optical
properties of transmission medium)
ω = angular frequency
λ = wavelength
δ = phase
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8. Electromagnetic radiation
• EM field emitted by different atoms will have
varying orientations and phases
• Resultant radiation may be described by
components of E field oscillating in xz and yz
planes with different amplitudes and phases:
Ex = Ex0 cos(ωt – 2πz/λ + δx)
Ey = Ey0 cos(ωt – 2πz/λ + δy)
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9. Types of polarized light
• 1. plane/linear:
• Vibration restricted to only one direction In
single meridian
• Linearly polarized light can be obtained from
the polariser such as Dichoric polarisers
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10. Linear polarization
• The two orthogonal
components are in phase
so that the ratio of the
strengths of two
components is constant
• The direction of the
electric vector (vector
sum of these two
components) is constant
so tip traces out as single
line in pane
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11. Dichoric polarisers
• Wire grid
• H- sheet (made of PVC)
• K- sheet – heat and humidity resistant (used in
sun glasses)
• J- sheet
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12. 2. Elliptical polarized
• Tip of the electric vector describes an ellipse
about the direction of propagation
• Equivalent to two plane polarised of unequal
magnitude (phase difference 90⁰)
• Vibration in an elliptical orbit
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13. Elliptical polarized
• Two components are
not in phase and either
do not have same
amplitude or are not
90⁰ out of phase,
though amplitude ratio
are constant
• Called so because their
electric vector traces
out an ellipse in the
plane
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14. 3.Circular polarized
• Wave in which the tip of the electric vector
describes a circle around the direction of
propagation
• Equivalent to two plane polarized waves of
equal magnitude moving together (out of
phase by 90⁰)
• Vibration is circular orbit
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15. Circular polarized
• One component is zero
while other is max. or
minimum amplitude
• Either x comp. can be 90⁰
ahead of y comp. or it can
be 90⁰ behind the y
comp.
• These cases are called
right handed circular
polarization and left hand
circular polarization,
depending upon way
electric vector rotates
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16. Few terms
• Polariser
an instrument by which
the light gets polarized
• Analyser
An instrument which
detects whether a light
ray is polarized or not
→polariser along with an
analyser constitute
polariscope
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17. Few related laws
• Malus law
• States that : when a beam of completely plane
polarized light is incident on an analyser, the
resultant intensity of light (I) transmitted from
the analyser varies directly and the square of
the cosine angle (θ) betn plane of
transmission of analyser and polariser
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18. Malus law
• Intensity emerging from polarizer is
IαE2
• Intensity emerging from analyser
I θ α E2
cos2
• Dividing 2 by 1
• We get I θ = I cos2
θ
• So when θ=90 , transmission axis of polariser and
analyser is perpendicular
I θ = 0.
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19. Brewster’s law
• States that when an unpolarized light is
incident at polarising angle φ on an interface
separating a rarer medium from a denser
medium such that the refractive index of the
denser medium is μ w.r.t the rarer medium ,
then the reflected light in the rarer medium is
completely polarised
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20. Brewster’s law
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21. Production of polarized light
1. Dichorism
2. Double reflection
3. Scattering
4. Reflection
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22. Dichorism
• Dichroism is selective absorption of the two
orthogonal incident natural light.
• It is physically anisotropic.
• Wire grid polariser
• In this parallel electrically conducting copper
wires are stretched between two insulating
boards.
• Here the x- component perpendicular to the wire
is transmitted while y-component parallel to the
wire is absorbed by the grid.
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24. • Dichroic crystals because of their anisotropic
structure. For eg tourmaline.
• Optic axis of the crystal is the specific
direction through which the electric field
component perpendicular to the axis is
strongly absorbed
• Only parallel electric field component is
transmitted.
• Dichroic means of two colours..
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25. Birefrenges/double reflection
• Optical anisotropy
• In some crystals the forces binding an electron
to the atomic nuclei is stronger in one
direction than another.
• When an electromagnetic wave act upon
them the electrons set into vibration in one
plane and hence emit the wave with same
energy and frequency in that plane at the end.
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26. Contd…
• Eg. Calcite/CaCO3
Symmetrical atoms arrangement about an
axis perpendicular to the carbonate plane
• Other birefrigent crystals
Ice land spar, Wallaston prism
• Birefringent polarisers
Nicol prism, Glan Foucalt prism
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27. A calcite crystal
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29. Scattering
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• Sky acts as a partial polariser due to the
scattering properties of air molecules
• Demonstration: viewing with crossed polaroid
• Scattering α λ-4 so blue wavelength scattered
more

30. Reflection
• When angle of incidence is equal to the angle
of polarization in any boundary, the reflected
ray is plane polarised with it’s electric field
vector parallel to the surface of reflection.
• When series of such reflecting surfaces are
aligned as in microscopes (slit lamp) the
reflected waves of all surfaces will form plane
polarised beam intense enough to produce
glare.
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31. Contd…
• So polaroid glasses with their transmission
axis perpendicular to the reflecting surface
would easily prevent the polarized intense
beam from reaching eye.
Brewester’s law: n= tan Ip
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32. Applications
1. To differentiate
longitudinal and
transverse wave
2. As sun glasses to cut of
unwanted reflected light
best utilized by fisherman,
motorist, skiers,
sportsman etc.
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33. Effect of polarizing filter in sky(right pic)
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34. • Similarly in driving ,the
light reflected from the
road surface and from
the painted or glass
surface of other
automobiles is also
partiallly
polarised,usually
horizontally
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35. Applications
3. Geology
Frequently exploited using
polarization microscopes,
for identifying minerals
photograph of a volcanic
sand grain: upper pic is
plane polarized light,
bottom pic is cross
polarized
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36. 4.Chemistry
• To check the chirality of the organic
compound
• Polarization is also used in infrared
spectroscopy
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37. 5. Astronomy
• For providing information on sources of
radiation and scattering, polarization probes
the interstellar magnetic field via Faraday
rotation
• Polarization of cosmic microwave background
is being used to study the physics of the early
universe
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38. 6. 3D movies
• Polarization is used for 3D movies ,in which
the images intended for each eye are either
projected from two different projectors
orthogonally oriented polarizing filters or,
more typically , from a single projector with
multiplexed polarization
• Polarized 3D glasses with suitable polarized
filters ensure that each eye receives only the
intended image
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39. 7. Communication and radar
applications
• All radio transmitting and receiving antennas
are intrinsically polarized, special use of which
is made in radar
• Vertical polarization is most often used when
it is desired to radiate a radio signal in all
directions such as widely distributed mobile
units
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40. Contd…
• AM and FM radio use vertical polarization,
while television uses horizontal polarization
• Alternating vertical and horizontal polarization
is used on satellite communications to allow
the satellite to carry two separate
transmission on given frequency
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41. 8.Material science
• In engineering , the relationship between
strain and birefringence motivates the use of
polarization in characterizing the distribution
of stress and strain in protypes
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42. 9. Navigation
• Sky polarization has been exploited in the “sky
compass”, which was used in the 1950s when
navigating near the poles of the Earth’s
magnetic field when neither the sun nor stars
were visible
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43. 10. To identify
thermally
tempered lenses
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44. 11.Haidinger’s brushes
phenomenon
• It is a entopic phenomenon
perceived by a normal eye
while observing in a surface
illuminated by plane –polarized
white light
• It appears as faint yellow
&blue-brush like pattern
radiating from the fixation point
with their long axis oriented at
rt.angle to the transmission
plane of polarization
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45. 12. Ophthalmic instruments
• Eliminate strong reflection from the patients
cornea
• Polariser 90⁰ to the polarisation of the
incident light
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46. 13.Polaroid vectograph(BV test)
• Stereogram picture : part of the picture
polarised at 900 to the other part by the plane
polariser placed in front of each eye – retinal
disparity – measure of stereopsis
• Other sensitive testing
Fixation disparity
Anisokonia
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48. References
• Optics by tunaclife
• Clinical optics
• Clinical visual optics
• Clinical refraction by Borish
• Clinical procedures in optometry
• Internet
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Thank