The document discusses the phenomenon of polarization of light. It defines polarization as restricting the electric vector vibrations of light along a plane. It describes the basics of plane waves and different states of polarization including linear, elliptical, and circular polarization. It discusses various methods by which light can become polarized, such as dichroism, reflection, scattering, and birefringence. Birefringence is defined as the splitting of a light ray into two rays with different refractive indices when passing through certain anisotropic materials.

1. POLARIZATION OF LIGHT Dr. J.K.GOSWAMY UIET, PANJAB UNIVERSITY, CHANDIGARH. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

2. WHAT IS POLARIZATION ? 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. It is the phenomenon of restricting the electric vector vibrations of the light along a plane which may or may not rotate about the direction of propagation.

4. UNPOLARIZED OR ORDINARY LIGHT 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. The electric vector amplitude is ~378 times greater than the magnetic vector amplitude. Hence the magnetic field vector oscillations can be ignored. Light wave can be approximated as constituted by electric field vector oscillating in all possible directions in a plane perpendicular to the direction of propagation of light.

7. Phenomenon of Polarization 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. The light vibrations have been restricted in vertical direction on passing through the polarizer 1. This phenomenon of restricting light vibrations along a specific direction is called Polarization . The plane in which light oscillations take place is called plane of vibration . The other plane devoid of light oscillations is called plane of polarization .

8. STATES OF POLARIZATION 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Linearly Polarized Light Elliptically Polarized light Circularly Polarized Light

14. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. REP: Right Elliptic Polarization (CW rotation of electric vector while approaching the observer) LEP: Left Elliptic Polarization (ACW rotation of electric vector while approaching the observer) An ellipse can be represented by 4 quantities: size of minor axis size of major axis orientation (angle) sense of rotation (CW or ACW) SENSE IN ELLIPTICAL POLARIZATION

17. METHODS OF POLARIZATION 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. DICHORISM REFLECTION SCATTERING BIREFRINGENCE

18. POLARIZATION BY DICHORISM 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Technique of selective absorption of electric vector vibrations in one of the two orthogonal directions.

20. DICHORISM 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Certain crystals strongly absorb the incident light oscillations along one direction while easily transmit the light oscillations in the direction perpendicular to it. The direction of strong absorption of electric vector is called absorption axis while other of easy propagation forms optic axis of the crystal. Tourmaline, Quartz

22. H-SHEET (GRID OF POLYMER CHAIN) 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. A sheet of polyvinyl alcohol is gently heated and stretched in a given direction resulting in alignment of hydrocarbons molecules into long molecular chains. It is then dipped in ink solution rich in iodine which impregnates the plastic and gets attached to long polymeric chain of molecules, effectively forming the chain of its own. The free electrons of iodine move along the chain as if they were long wires. The electric field component of light parallel to chain gets absorbed while the perpendicular component is easily transmitted. In H-sheets, there is no hazy appearance as scattering is caused by molecules rather than submicroscopic crystals. The H-sheets are effective polarizers over entire visible spectrum.

24. POLARIZATION BY REFLECTION 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Transparent surfaces reflect selectively one component of electric vector vibrations at a particular angle of incidence.

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28. BREWSTER’S LAW 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. From Fresnel's equations, it can be determined that the parallel reflection coefficient is zero when the incident and transmitted angles sum to 90°. The use of Snell's law gives an expression for the Brewster angle.

29. POLARIZATION BY STACK OF PLATES 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

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31. POLARIZATION BY SCATTERING 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Scattering of light in orthogonal direction yields polarized light.

33. POLARIZATION BY SCATTERING 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

34. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. POLARIZATION BY SCATTERING

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36. DOUBLE REFRACTION OR BIREFRINGENCE 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Anisotropic media splits ordinary light into two purely polarized beams having vastly different properties .

43. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Uniaxial Material n o n e Δn =n e -n o Beryl Be 3 Al 2 (SiO 3 ) 6 1.602 1.557 -0.045 Calcite CaCO 3 1.658 1.486 -0.172 Calomel Hg 2 Cl 2 1.973 2.656 +0.683 Ice H 2 O 1.309 1.313 +0.004 Magnesium fluoride MgF 2 1.380 1.385 +0.006 Quartz SiO 2 1.544 1.553 +0.009 Ruby Al 2 O 3 1.770 1.762 -0.008 Rutile TiO 2 2.616 2.903 +0.287 Sapphire Al 2 O 3 1.768 1.760 -0.008 Sodium nitrate NaNO 3 1.587 1.336 -0.251 Tourmaline (complex silicate ) 1.669 1.638 -0.031 Zircon, high ZrSiO 4 1.960 2.015 +0.055

46. NICOL PRISM CONSTRUCTION 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. 71 o A A’ B D C’ C E-ray O-ray 68 o

48. MALUS LAW 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

49. LAW OF MALUS Amplitude of light transmitted by polarizer: Intensity = Const .(Amplitude) 2 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

50. CROSSED POLARIZERS 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

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52. ANALYSIS OF LIGHT 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. It is the procedure to umambiguously determine the state of polarization of given light wave.

57. DETERMINATION OF STATE OF POLARIZATION 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Polaroid introduced in the path of light and rotated about axis coinciding with direction of propagation of light. There is ambiguous situation in obtaining state of polarization in situations 2 and 3. 1. Complete extinction of intensity at two orientations of polariod Linearly polarized beam 2. No variation in the beam intensity Unpolarized Circularly polarized Unpolarized + Circularly polarized 3. Intensity variation but not complete extinction Elliptically polarized. Unpolarized + linearly polarized Unpolarized + Elliptically polarized.

63. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. OPTICAL ACTIVITY When a substance rotates the plane of plane polarized light, it is optically active and the phenomenon is referred to as optical activity. Dextrorotatory rotates the plane of polarized light in clockwise direction when viewed through a polarimeter. (+) or ( d ) do not confuse with D Levorotatory rotates the plane of polarized light in counter-clockwise direction when viewed through a polarimeter. (-) or ( l ) do not confuse with L

64. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Specific Rotation is the angle of rotation of plane polarized light by a 1.00 gram per cm -3 sample in a 1 dm tube. [ α ] D (D = sodium lamp, λ = 589 nm) where α = observed rotation l = length (dm) d = concentration (g/cm 3 ) Alanine [ α ] D = +8.5 Lactic acid [α ] D = -3.8 The angle of rotation of plane polarized light by an optically active substance is proportional to the number of atoms in the path of the light.

65. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. SCHEMATIC DIAGRAM OF A POLARIMETER An instrument used to measure optical activity. Analyzer Sample tube Light source Polarizer Eye Rotation of analyzer

68. APPLICATIONS OF POLARIZATION 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

69. POLARIZING FILTERS Polarizing filters exclude all light not vibrating in the preferred direction of the filter. Light reflected by shiny transparent material is partly or fully polarized, except when the light is normal to the surface. Polarizing sunglasses, by orienting their polarizing material vertically, selectively exclude the polarized portion of light reflected by the horizontal surface. 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

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75. Visual Effects of Polarization 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. Polarization Photography Without Polarizer With Polarizer Polarization by scattering is observed as light passes through the atmosphere. The scattered light produces the brightness and color in clear sky. This partial polarization of scattered light can be used to darken the sky in photographs, increasing the contrast.

76. Polarization Photography : Reduces Reflections Visual Effects of Polarization….cont’d 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

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81. STOKES PARAMETERS 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. In 1852 Sir George Gabriel Stokes took a very different approach and discovered that polarization can be described in terms of observables using an experimental definition.

82. STOKES PARAMETERS 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C. The polarization ellipse is only valid at a given instant of time (function of time): To get the Stokes parameters, do a time average (integral over time) and a little bit of algebra... The 4 Stokes parameters are:

84. STOKES PARAMETERS …..cont’d 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.

85. THANKS FOR NICE AUDIENCE 09/10/10 Polarization of light : Dr. J.K. Goswamy, UIET, P.U.C.