K L University By G.SUNITA DEPARTMENT OF PHYSICS

Lecture 02 & 03 Polarization of Light

Polarization… L ight is an electromagnetic wave. E M waves are those waves in which there are sinusoidal variation of electric and magnetic fields at right angles to each other as well as to the direction of propagation of wave.

Applications: 5 Photographic Filters 3 D films Polarization…

6 Liquid Crystal (LCD) Displays Stress Analysis Polarization…

Polarization

Polarization…  The light which acquired the property of one-sidedness (Direction of vibration) is called polarized light.  The un-polarized light consists of an infinite number of waves, each having its own direction of vibration.

Polarization…  From Sun, bulbs, candles  No fixed plane of oscillation  Random changes in direction of light  Filtered Light  Fixed plane of oscillation  Half of the intensity of unpolarized light

Polarization…

Filters to transform un-polarized light to polarized light Polaroid filter Enables only 1 polarization of light to pass through.

12 Polarization…

13 Polarization…

14 Polarization… Tourmaline crystal plate

15 Polarization… Malus' law. When a perfect polarizer is placed in a polarized beam of light, the intensity I of the light that passes through is given by equation I=I 0 cos 2 θ, where θ is the angle between the light's initial polarization direction and the axis of the polarizer.

Polarization…

Polarization…

21 Pictorial polarized light Vertically Polarized light ( п – vibration ) Horizontally Polarized light ( σ – vibration) Polarization… Un Polarized light ( п & σ – vibration)

Polarization… Plane of vibration and Plane of polarisation

23 Polarization… Production of Polarized Light by different methods:  By Reflection - Brewster’s angle  By Refraction  By Double refraction – Birefringence  By Scattering - Light from the sky  By Selective absorption - Polaroid filter

24 Polarization…

25 Polarization… XY N N1 P O Q R Polarization by Reflection I = p r = p r. N1 R...

Polarization… Polarization by Reflection Brewster’s law- That the tangent angle of polarization (p) is numerically equal to the refractive index(µ) of the medium.

Polarization… a) horizontally b) vertically horizontal vertical direction of polarization of reflected light

Polarization… wearing sunglasses will help reducing glare (reflection) from flat surfaces (highway/water) withoutwith sunglasses

Polarization… Pile of plates Polarizing angle for glass: 57.5 Inclined at 32.5 Transmitted light is partially polarized

Polarization… Purely plane polarized

Polarization…

Geometry of Calcite Crystal : K nown as Iceland spar. I t is colourless crystal. I t is transparent to ultraviolet and visible light. I t belongs to rhombohedral class of hexagonal system. C alcium carbonate (CaCO3). T he six faces are parallelograms each having angles 101 o 55 ’ a nd 78 o 5.

33 Calcite Crystal : CaCO3 Blunt Corner Optic axis Principle section Uniaxial crystals Biaxial crystals KLU

Optic axis : 34 An imaginary line passing through one of the blunt corners and making equal angles with all the three faces is called optic axis. Optic axis is not an imaginary line but it is a direction. Any line parallel to optic axis also acts as optic axis. Polarization…

36 Double Refraction : (Birefringence) Experiment Polarization… Anisotropic substance : physical prop. are different

Polarization…

O E

39 Double Refraction : (Birefringence) Polarization…

40 Double Refraction : (Birefringence) Polarization… Refractive indices: In case of calcite: When both rays are travel with same velocity along optic axis.

Significance of optical Axis

Polarization… 1.Principle 2.Construction 3.Action 4.Limitations 5.Uses Calcite canada balsam O ray E ray

Principle : Optical Device. Double Refraction Transmit extra-ordinary ray and cut off ordinary ray Construction: Length is 3 times as its width End Faces grounded – 68 and 112 instead of 71 and 109 Cut into two pieces – grounded – polished – cemented (With Canada balsam). Polarization…

µₒ = µ e = µ canada balsam = 1.55

Polarization… Action: Light entered the faces Canada balsam acts as Rarer medium for O-ray Denser medium for E-ray E-ray: Straight line Plane polarized O-ray: Total internal reflection > critical angle

Polarization… Limitations: 1.Much smaller than the ∠ SMB with face AB – O-ray strikes less than Ө c Both O-ray and E-rays transmitted Angle of incidence : 14 ◦ 2.Angle grater than ∠ SMB with face AB -- E-ray will refract suffer total reflection --- No light To obtain plane polarized light, the incident beam should be confined with an angle of 14 on either side of SM

Polarization… Uses: Polarizer Analyzer

Polarization… 1. A Ray of light is incident on the surface of glass plate µ=1.56 at the polarizing angle. Calculate the angle of refraction. 2. Calculate the Brewster angle for the following liquids Ethyl alcohol, µ=1.361 Carbon tetrachloride µ= The velocity of light in water is 2.2*10 8 m/s. What is the polarizing angle of incidence foe water surface? (c=3.8*10 8 m/s)

Huygens Theory of Double refraction Negative BirefringencePositive Birefringence

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Polarization… Types of polarized lights Detection and production of PPL Production of CPL &EPL Nicol’s prism