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# Polarization of Light and its Application (healthkura.com)

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.............

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

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### Polarization of Light and its Application (healthkura.com)

1. 1. POLARIZATION OF LIGHT & ITS APPLICATION BIKASH SAPKOTA Bachelor of Optometry 16th Batch Maharajgunj Medical Campus, Nepal
2. 2. Concept of Polarization Types of Polarization Methods of achieving Polarization Applications of Polarization PRESENTATION LAYOUT
3. 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. 4. Electric field vector Magnetic field vector Em wave
5. 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. 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. 7. . Polarization
8. 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
9. 9. 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
10. 10. TYPES OF POLARIZATION 1. Linear Polarization 2. Circular Polarization 3. Elliptical Polarization
11. 11. LINEAR POLARIZATION Plane polarized wave Electric field vector oscillates along a straight line in one plane
12. 12. Resultant wave is linear in vertical plane Resultant wave is linear in 450 plane
13. 13. 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
14. 14. 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)
15. 15. Blue wave is resultant circular polarized wave .
16. 16. . Superposition of oppositely polarized waves results in to plane polarized wave
17. 17. 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
18. 18. Blue wave is resultant elliptical polarized wave Green wave is resultant elliptical polarized wave
19. 19. METHODS OF ACHIEVING POLARIZATION 1. Reflection 2. Scattering 3. Dichroism 4. Birefringence
20. 20. 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
21. 21. 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
22. 22. A:no polarizer used B:vertical polarizer used C:horizontal polarizer used A B C
23. 23. 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
24. 24. . 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
25. 25. 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
26. 26. 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
27. 27. 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
28. 28. 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
29. 29. 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:
30. 30. 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
31. 31. Intensity is maximum if the transmission axes are parallel and intensity is zero if the transmission axes are perpendicular to each other
32. 32. APPLICATIONS OF POLARIZATION OF LIGHT .
33. 33. 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
34. 34. Fishermen use polaroid sun glasses to locate fish under water . Without polaroid sun glasses With polaroid sun glasses
35. 35. Polaroid sun glasses are also used to reduce head light glare of car . Without polaroid sun glasses With polaroid sun glasses
36. 36. 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
37. 37. Any specimens in glass cases can be well photographed by using filters No polarizerVertical polarizerHorizontal polarizer
38. 38. 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
39. 39. Titmus Fly Test
40. 40. 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
41. 41. Application of Polarization by Birefringence In birefrigent biprisms Birefrigent biprisms such as nicol, glan-foucault and wollaston are used to produce polarized light
42. 42. Wollaston prism Glan foucault prism
43. 43. 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
44. 44. 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
45. 45. 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
46. 46. 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
47. 47. 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
48. 48. Mineral concentration
49. 49. Other Applications of Polarization .
50. 50. 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
51. 51. 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
52. 52. 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
53. 53. stress analyser . Stress analysis
54. 54. 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
55. 55. In Slit Lamp and Ophthalmoscope Control unwanted reflections eg. that from the front of cornea Red filter,blue filter,green filter etc.
56. 56. 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
57. 57. . 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
58. 58. . 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
59. 59. . 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
60. 60. . 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
61. 61. REFERENCE •Optics by Tunnacliffe •Optics and Refraction by A.K. Khurana •Principle of Physics, Ayam Publication •Internet
62. 62. Palanchowk Bhagawati
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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

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