Download link ❤❤https://healthkura.com/eye-ppt/29/❤❤ Dear viewers Check Out my other piece of works at ❤❤❤ https://healthkura.com/eye-ppt/ ❤❤❤ polarization of light & its application. PRESENTATION LAYOUT Concept of Polarization Types of Polarization Methods of achieving Polarization Applications of Polarization POLARIZATION Transforming unpolarized light into polarized light Restriction of electric field vector E in a particular plane so that vibration occurs in a single plane Characteristic of transverse wave Longitudinal waves can’t be polarized; direction of their oscillation is along the direction of propagation............. For Further Reading •Optics by Tunnacliffe •Optics and Refraction by A.K. Khurana •Principle of Physics, Ayam Publication •Internet

1. POLARIZATION OF LIGHT
& ITS APPLICATION
BIKASH
SAPKOTA
Bachelor of Optometry
16th Batch
Maharajgunj Medical
Campus, Nepal

2. Concept of Polarization
Types of Polarization
Methods of achieving Polarization
Applications of Polarization
PRESENTATION LAYOUT

3. ORDINARY LIGHT
Electromagnetic wave
Electric field E and magnetic field B are:
oPerpendicular to each other
oIn phase
oAlso perpendicular to the direction of
propagation

4. Electric field vector
Magnetic field vector
Em wave

5. ORDINARY LIGHT
Unpolarized Light
oContains large no.of atoms producing
waves with particular orientation of
electric vector E
oResultant wave:unpolarized
wave:superposition of waves vibrating in
all possible directions

6. POLARIZATION
Transforming unpolarized light into polarized light
Restriction of electric field vector E in a particular
plane so that vibration occurs in a single plane
Characteristic of transverse wave
Longitudinal waves can’t be polarized; direction of
their oscillation is along the direction of
propagation

7. .
Polarization

8. Plane of vibration
A plane including the direction of light propagation
and the direction of electric field
Plane of polarization
The plane perpendicular to the plane of vibration

10. Why only electric field vector is considered in
polarization and not magnetic field vector?
 Maxwell’s Equation
E=c × B
 c is velocity of light(c=3 × 10
8
m/s),very large value
E>>>B i.e. Em wave is predominantly an electric
wave
To change any characteristics of Em wave, including
polarization,E should be affected

11. TYPES OF POLARIZATION
1. Linear Polarization
2. Circular Polarization
3. Elliptical Polarization

12. LINEAR POLARIZATION
Plane polarized wave
Electric field vector oscillates along a
straight line in one plane

13. Resultant wave is linear in vertical plane
Resultant wave is linear in 450
plane

14. Superposition of plane polarized wave
Two plane polarized waves are added according to
the rules of vector addition
Results in a linear,elliptical or circular polarized wave
depending on the amplitude and the phase shift
between two waves

15. CIRCULAR POLARIZATION
 Consists of two perpendicular plane Em waves
with equal amplitude and 900
phase difference
 Plane of oscillation rotates around the
propagation axis
 May be right circularly polarized(clockwise) or
left circularly polarized(counterclockwise)

16. Blue wave is resultant circular polarized wave
.

17. .
Superposition of oppositely polarized waves results in to plane
polarized wave

18. ELLIPTICAL POLARIZATION
 Consists of two perpendicular waves of unequal
amplitude that differ in phase by 900
 The tip of the resultant electric field vector
describes an ellipse in any fixed plane
intersecting and normal to the direction of
propagation
 Circular and linear polarization:special cases of
elliptical polarization

19. Blue wave is resultant elliptical polarized wave
Green wave is resultant elliptical polarized wave

20. METHODS OF ACHIEVING
POLARIZATION
1. Reflection
2. Scattering
3. Dichroism
4. Birefringence

21. POLARIZATION BY REFLECTION
Unpolarized light can undergo polarization by
reflection off of non metallic surfaces like snow, glass
Incident angle is such that angle between reflected
and refracted ray is 900
Such incident angle is k/a polarizing angle or
Brewster’s angle
Reflected ray is linearly polarized parallel to the
reflecting surface

23. BREWSTER’S LAW
When light is incident at polarizing angle:
The tangent of polarizing angle=Refractive index of
material
i.e, tan θ= µ
For Sapphire, µ=1.77
So, θ=tan-1
(1.77)=60.5350
 If the angle of incidence
is not exactly the Brewster’s
angle the reflected ray will
only be partially polarized

24. A:no polarizer used
B:vertical polarizer used
C:horizontal polarizer used
A
B
C

25. POLARIZATION BY SCATTERING
Polarization also occurs when light is scattered
When light strikes the atoms of a material, electrons
are set into vibration
Vibrating electrons produce new Em waves radiated
in all possible directions
Newly generated waves strike neighbouring atoms,
thereby continuing the process
Absorption + re emission →scattered light

27. .
Light scattering off atoms is:
•Unpolarized if the light keeps traveling in the same
direction
•Linearly polarized if it scatters in a direction
perpendicular to the path it was travelling
•Somewhere between linearly polarized and
unpolarized if it scatters off at any other angles

28. POLARIZATION BY BIREFRINGENCE
Polarization due to double refraction
A double refracting crystals like Iceland spar, calcite
refracts incident light into two different paths
So if an object is viewed by looking through the crystal,
two images are seen
Polarizing filter can be used to completely block one
image
Two rays are formed because they have different
speeds due to two index planes in the medium

29. O-ray:passes undeviated,ordinary wave
E-wave:beam displaced sideway,extraordinary wave
Both beams thus formed are polarized:
One parallel to the surface
Other perpendicular to the surface

30. POLARIZATION BY DICHROISM
Polarization by selective absorption
Such crystals are used which transmits wave whose
electric field vibrates in a particular plane and absorbs
electric field vibrating in other planes
Eg. Tourmaline polaroid

31. Polaroids
The most common method of polarization involves
the use of polaroid
Have long chain of molecules that are aligned within
the filter in a particular direction
When an unpolarized light falls on a polaroid:
 The electric vector E oscillating in the direction of the
alignment of molecules of the polaroid is absorbed
 Electric field vector oscillating perpendicular to the
direction of the alignment of molecules pass through the
polaroid
Transmitted light is plane polarized

33. Dual Filter:Polarizer + Analyzer
If the transmission axes of polarizer and analyzer are
perpendicular, no light is transmitted
The light transmitted at other angles follows the Law
of Malus
Polarizer and analyzer relation can be best described
by picket fence analogy:

35. Law of Malus
When a beam of completely plane polarized light is
incident on an analyzer, the resultant intensity of light
(I) transmitted from the analyzer varies directly as the
square of the cosine angle (θ) between plane of
transmission of analyzer and polarizer
i.e ,I ἀ cos2
θ
I = I0cos2
θ
Where, I0 is the intensity of polarized light transmitted
through a polarizer
Mind It!! I0 is half the intensity of unpolarized light
incident on the polarizer

36. Intensity is maximum if the transmission axes are parallel
and intensity is zero if the transmission axes are
perpendicular to each other

37. APPLICATIONS OF POLARIZATION OF
LIGHT
.

38. Application of polarization by reflection
In polaroid sunglasses
Light reflected off a pool of still water is partially
polarized parallel to water surface
This gives rise to glare
The transmission direction of polaroid sheet in sun
glasses is vertical which blocks horizontal components
of light
Hence reduce intensity and glare

39. Fishermen use polaroid sun glasses to locate fish under
water
.
Without polaroid sun glasses With polaroid sun glasses

40. Polaroid sun glasses are also used to reduce head light
glare of car
.
Without polaroid sun glasses With polaroid sun glasses

41. In Photographic Filters
Glare caused by reflected light off water surface makes
it harder to see behind water surface
So photographers often use filters to cut out glare and
get better pictures

43. Any specimens in glass cases can be well
photographed by using filters
No polarizerVertical polarizerHorizontal polarizer

44. Application of Polarization by Dichroism
In Titmus Stereo Test
Makes use of victograph
The right eye and left eye pictures are polarized at
450
and 1350
respectively
The pictures are viewed through a correspondingly
oriented spectacle analysers
In normal eye, a perception of depth i.e. stereo is
produced when the brain fuses the two images

45. Titmus Fly Test

46. Application of Polarization by Scattering
Photographic secret of capturing a vivid blue sky
using polaroid filter
No polaroid filter has
been used
Horizontal polarizer used
Deep blue sky
Vertical polarizer used
No significant difference

47. Application of Polarization by Birefringence
In birefrigent biprisms
Birefrigent biprisms such as nicol, glan-foucault and wollaston
are used to produce polarized light

48. Wollaston prism
Glan foucault prism

49. In Liquid Crystal Displays(LCD)
There are some crystals that become aligned when
an electric field is put across them
When this happens they act as polarizing filters
LCD

50. In Retinal Diagnosis
Polarization Sensitive Optical Coherence Tomography
(PS-OCT) is used to measure the thickness and
birefringence of the Retinal Nerve Fibre Layer(RNFL)
Birefringence change of the RNFL can serve as an early
indicator of glaucoma

52. In Polarized Snellen Eye Chart
Special polarizing glass is used:OD polarized at 900
and OS polarized at 1800
Test one eye at a time though patient viewing
binocularly
Alternative lines of optotype are also polarized at 900
and 1800
Use to detect
malingering

53. To detect defect in Intra Ocular Lenses
Birefringence is detected by placing the lens between
two linear polarizers at right angles to each other
Any light transmitted appears as a readily recognizable
bright spot
The bright spot indicates a possible defect in the
strength of the lens

54. In Polarized Light Microscopy
Use of polarized light to illuminate birefrigent
sample
Directly transmitted light can, optionally, be blocked
with a polarizer oriented at 900
to the illumination
Polarized light interacts strongly with the sample
and so generating contrast with the background
It is used extensively in optical mineralogy

55. Mineral concentration

56. Other Applications of Polarization
.

57. Haidinger’s Brush
Yellowish bow tie shaped
Entoptic phenomenon
Always positioned in macula, so visible in centre of
visual field
Viewed while facing away from sun,bright
background,eg LCD screen
Due to dichroism of xanthophyll pigment of macula
Used in Eccentric Fixation:utilized to train people with
strabismus to look at objects with their fovea rather
than their eccentric retinal zone

58. IN 3D Films
Two films shown at same time through two projectors
Projected through polarizing filters with axes
perpendicular to each other
Viewers wear glasses with 2 polaroid filters with axes
perpendicular
Left eye sees the movie projected from right
Right eye sees movie projected from left
This gives viewers a perception of depth

60. Photoelasticity:Stress Analysis
When light passes through some materials its plane
of polarization is rotated i.e optical activity
The thicker the material the more it is rotated and
different colours are rotated by different amounts
To investigate the stress in an engineering part a
model is made in plastic,pass light through and put
it under stress
The deformed spot is located by analysing the
coloured pattern produced

61. stress analyser
.
Stress analysis

62. In Saccharimetry
Measurement of concn
of sugar in solution
Due to molecular structure of sugar,these solution
rotate the plane of polarization as light passes
through them
 rotation may be right-handed(dextro) or left-
handed(laevo)
Saccharimeter

63. In Slit Lamp and Ophthalmoscope
Control unwanted reflections eg. that from the front of
cornea
Red filter,blue filter,green filter etc.

64. Multiple choices questions
1.Optically active substances are those substances which
a. Produce polarized light
b. Produce double refraction
c. Convert a plane polarized light into circular polarized
light
d. Rotate the plane of polarization

65. .
2.An unpolarized light wave is traveling along positive X-axis.
The electric field vector in the beam vibrates in the direction
of
a. Positive Y-axis definitely
b. Negative X-axis
c. Positive X-axis
d. Y or Z-axis

66. .
3.A calcite crystal is placed over a dot on a piece of paper
and rotated. On seeing through the calcite, one will see
a. Two rotating dots
b. Two stationary dots
c. One dot only
d. One dot rotating about the other

67. .
4. An unpolarized beam of transverse waves is one whose
vibrations
a. Are confined to a single plane
b. Occur in all directions perpendicular to the direction of
propagation
c. Are confined to a single plane perpendicular to the
direction of propagation
d. Occur in all directions

68. .
5.Two polaroids are placed with their transmission
axis at 900
to each other and transmitted
Intensity of light is zero. If one more polaroid is
placed between these two, bisecting the angle
between them, then the ratio of transmitted
intensity of light to the intensity of unpolarized light
will be
a. 1/4
b. 1/8
c. 1/2
d. 0

69. REFERENCE
•Optics by Tunnacliffe
•Optics and Refraction by A.K. Khurana
•Principle of Physics, Ayam Publication
•Internet

70. Palanchowk Bhagawati