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POLARIZATION OF LIGHT & ITS APPLICATION
RAMACHANDRA COLLEGE OF ENGINEERING, ELURU K LOKESWARA RAO Asst professor
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PRESENTATION LAYOUT Concept of Polarization Types of Polarization
Methods of achieving Polarization
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Electric field E and magnetic field B are:
ORDINARY LIGHT Electromagnetic wave Electric field E and magnetic field B are: Perpendicular to each other In phase Also perpendicular to the direction of propagation
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Electric field vector Magnetic field vector
Em wave
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ORDINARY LIGHT Unpolarized Light
In a beam of light, if the oscillations of E vectors are in all directions in a plane perpendicular to the direction of propagation, then the light is called unpolarized light.
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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
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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 × 108 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
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. Polarization
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Plane of vibration Plane of polarization
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
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Linear Polarization Circular Polarization 3. Elliptical Polarization
TYPES OF POLARIZATION Linear Polarization Circular Polarization 3. Elliptical Polarization
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LINEAR POLARIZATION Plane polarized wave
The electric field of light is confined to a single plane along the propagation direction in linear polarization.
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Resultant wave is linear in vertical plane
Resultant wave is linear in 450 plane
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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
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CIRCULAR POLARIZATION
The electric field of light has two linear components that are perpendicular to each other and have identical amplitudes, but the phase difference is π ⁄ 2 (or) 900. The electric field that occurs will propagate in a circular motion. May be right circularly polarized(clockwise) or left circularly polarized(counterclockwise)
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Blue wave is resultant circular polarized wave
. Blue wave is resultant circular polarized wave
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. Superposition of oppositely polarized waves results in to plane polarized wave
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ELLIPTICAL POLARIZATION
The electric field of light propagates along an elliptical path. The two linear components do not have the same amplitude and phase difference. 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
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Blue wave is resultant elliptical polarized wave
Green wave is resultant elliptical polarized wave
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METHODS OF ACHIEVING POLARIZATION
Reflection Scattering Dichroism or Selective absorption Birefringence or Double refraction
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POLARIZATION BY REFLECTION
When the light is allowed to be incident on a non metallic surfaces like snow, glass at particular angle, the reflected beam is completely plane polarized. Incident angle is such that angle between reflected and refracted ray is 900 Such incident angle is known as polarizing angle or Brewster’s angle Reflected ray is completely linearly polarized and vibrations are perpendicular to the plane of incidence.
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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)= If the angle of incidence is not exactly the Brewster’s angle the reflected ray will only be partially polarized
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Malus law It helps us to study the relation of the intensity of light and the polarizer-analyzer. It states that the intensity of plane-polarized light that passes through an analyzer varies directly with the square of the cosine of the angle between the plane of the polarizer and the transmission axes of the analyzer.
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The intensity of the incident light on the analyzer ‘I0’ is directly proportional to the square of the amplitude of the electric vector ‘E0’. I ∞ E02 The intensity ‘I’ of light transmitted by the analyzer is, I ∝ (E0 x cosθ)2 Hence, I / I0 = (E0 x cosθ)2/E02 = cos2θ I = I0 x cos2θ Therefore, I ∝ cos2θ
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