Polarization

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POLARIZATION
TOPICS  POLARIZATION OF ELECTROMAGNETIC WAVES  POLARIZING SHEETS

 POLARIZATION BY REFLECTION
 DOUBLE REFRACTION  CIRCULAR POLARIZATION

 POLARIZATION BY SCATTERING
Text Book: PHYSICS VOL 2 by Halliday, Resnick and Krane (5th Edition) MIT-MANIPAL BE-PHYSICS-POLARIZATION-2011-12 1

POLARIZATION OF ELECTROMAGNETIC WAVES

• By convention, we define the direction of polarization of the wave to be the direction of the electric vector. • The plane determined by electric vector and direction of propagation of wave is called plane of polarization (xy plane in figure)

Plane electromagnetic wave

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POLARIZATION OF ELECTROMAGNETIC WAVES

Example: Polarized Microwaves
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POLARIZATION OF ELECTROMAGNETIC WAVES
(a)Representation of a linearly polarized wave with the electric field vibrating in the vertical direction viewed from along the direction of propagation. (b)Representation of an unpolarized wave viewed along the direction of propagation (perpendicular to the page). The transverse electric field can vibrate in any direction in the plane of the page with equal probability. (c)An equivalent representation of the unpolarized wave, as two waves linearly polarized at right angles to one another and with a random phase difference between them. MIT-MANIPAL BE-PHYSICS-POLARIZATION-2011-12 4

POLARIZING SHEETS
Polaroid  Polarizing material The polarizing direction is established during the manufacturing process. If E is the magnitude of electric vector, only E cos  (y component) passes through the polaroid. Transmitted intensity I = Im cos2  [Law of Malus] where Im  maximum intensity (ie  = 0 or 180 degree) MIT-MANIPAL BE-PHYSICS-POLARIZATION-2011-12 5

POLARIZING SHEETS

Two polarizing sheets whose transmission axes make an angle  with each other. Only a fraction of the polarized light incident on the analyzer is transmitted through it.

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POLARIZING SHEETS
Problem: SP44-1 Two polarizing sheets have their polarizing directions parallel so that the intensity Im of the transmitted light is a maximum. Through what angle must either sheet must be turned if the intensity is to drop by one-half?

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POLARIZING SHEETS
Problem: E44-1 The magnetic field equations for an em wave in space are Bx = B sin (ky + t), By = Bz = 0. (a) What is the direction of propagation? (b) Write the electric field equations. (c) Is the wave polarized? If so, in what direction?

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POLARIZING SHEETS
Problem: E44-8 A beam of light is linearly polarized in the vertical direction. The beam falls at normal incidence on a polarizing sheet with its polarizing direction at 58.8 to the vertical. The transmitted beam falls, also at normal incidence, on a second polarizing sheet with its polarizing direction horizontal. The intensity of the original beam is 43.3 W/m2. Find the intensity of the beam transmitted by the second sheet.

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POLARIZING SHEETS
Problem: E44-9 Suppose that in exercise 8 the incident beam was unpolarized. What now is the intensity of the beam transmitted by the second sheet?

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POLARIZATION BY REFLECTION When light is incident on the surface of a dielectric material at polarizing angle of incidence, (θp= Brewster’s angle) the reflected light is completely plane polarized and the transmitted ray is perpendicular to reflected ray.

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POLARIZATION BY REFLECTION n = tan θp This expression is called Brewster’s law, and the polarizing angle θp is sometimes called Brewster’s angle. Because n varies with wavelength for a given substance, Brewster’s angle is also a function of...
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