Polarization of Light and its Application (healthkura.com)
132 likes73,550 views
The document discusses the polarization of light, explaining its concept, types (linear, circular, elliptical), and methods of achieving it (reflection, scattering, dichroism, birefringence). It details polarization's applications in areas like photography, optical testing, and medical diagnostics, emphasizing its significance in reducing glare and enhancing image quality. The document also includes multiple choice questions to reinforce understanding of the concepts presented.
More Related Content
Similar to Polarization of Light and its Application (healthkura.com) (20)
Polarization of Light and its Application (healthkura.com)
- 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
- 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
- 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
- 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