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PC20312 Wave Optics Section 2: Polarization
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Polarization states Image from Wikipedia linearcircularelliptical
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Linear and circular polarization http://physics-animations.com/Physics/AVI/ellf.avi
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Dipole radiation http://physics.usask.ca/~hirose/ep225/radiation.htm http://www-antenna.ee.titech.ac.jp /~hira/hobby/edu/em/dipole2/dipole2.html E Optical E-field……drives oscillating dipoles in the medium… …which radiate in all directions except parallel to E. www.harvard.edu/~efortin/thesis/html/EMR_light.shtml
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Polarization by reflection Click here for a web-based animation of Brewster’s angle E perpendicular to plane of incidence “s-polarised” Emission always max in direction of E r E parallel to plane of incidence “p-polarised” Emission amplitude varies with direction of E r EiEi ErEr EtEt EiEi ErEr EtEt
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Brewster’s angle, B Sir David Brewster 1781-1868 EiEi E r =0 EtEt tt BB ntnt nini P-polarised light
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Polarization by scattering E in vertical no vertical scattering E in horiz. no horiz. scattering Animation from http://www-antenna.ee.titech.ac.jp/~hira/hobby/edu/em/smalldipole/force.gif For unpolarised incident light the scattered light is: Completely polarised in vertical horiz directions Partially polarised in intermediate directions unpolarised polarised partially polarised
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Polarized light in nature Image from Wikipedia Unfiltered imageImage seen through polarising filter
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Polaroid PVA structure from http://wwwchem.csustan.edu/CHEM2000/EXP2/bkg.htm Polaroid sheet eg aligned PVA molecules E cos E sin E cos E-field component aligned with long axis of molecule is absorbed E
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Malus’ Law Etienne-Louis Malus 1775-1812 http://physics-animations.com/Physics/AVI/polariz.avi
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Anisotropic Materials Image from Wikipedia Calcite CaCO 3 EyEy ExEx PyPy PxPx n o = 1.658 & n e =1.486 (at =590 nm) For calcite:
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Birefringence E o perpendicular to k & optic axis E e perpendicular to E o z y x k EoEo EeEe Optic Axis EoEo
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Double Refraction Image from Wikipedia unpolarised light Optic Axis e-ray o-ray For calcite, typical angle between beams ~6
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Polarizing Beamsplitter polarised light unpolarised light Optic Axis points towards you polarised light calcite transparent glue o-ray e-ray Photo from http://www.lightmachinery.com
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Waveplates Optic Axis d z y x n o >n e : Optic Axis is ‘fast’ n e >n o : Optic Axis is ‘slow’ Photo from http://www.lightmachinery.com In this diagram, is the optic axis slow or fast?
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The Faraday Effect Image from http://en.wikipedia.org/wiki/Faraday_effect Material V (rad.T -1.m -1 ) Glass 9.2 10 -4 Water 3.8 10 -4 Air 1.8 10 -7 Quartz 4.8 10 -4 Terbium Gallium Garnet -40
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Faraday Isolator 45 P1P1 P2P2 E B P1P1 P2P2 B E
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