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Introduction A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. Common types are,
- 1. Linear polarizers
- 2. Circular polarizers
Optical polarizers By - Kamalesh 19-04-2013 Introduction A - - PowerPoint PPT Presentation
Optical polarizers By - Kamalesh 19-04-2013 Introduction A - - PowerPoint PPT Presentation
Optical polarizers By - Kamalesh 19-04-2013 Introduction A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. Common types are, 1. Linear polarizers 2. Circular polarizers
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Linear polarizers
- 1. Absorptive polarizers
- 2. Beam splitting polarizers
Wire grid polarizer - For practical use, the separation distance between the wires must be less than the wavelength of the radiation, and the wire width should be a small fraction of this distance. Hence generally only used for microwaves and for far- and mid-infrared light.
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Absorptive polarizers
- 1. Dichroic crystals – They have preferential absorption of light which is
polarized in particular directions. Eg. Tourmaline, herapathite etc.
- 2. A Polaroid polarizing filter - It is made from polyvinyl alcohol (PVA) plastic
with an iodine doping.
- 3. A modern type of absorptive polarizer is made of elongated silver
nanoparticles embedded in thin (≤0.5 mm) glass plates. Provide polarization ratios as high as 100,000:1
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Beam splitting polarizers
- For most of beam-splitting polarizers, only one of the two output beams is
fully polarized. The other contains a mixture of polarization states.
- Suitable for use with high intensity beams such as laser light.
Polarization by reflection - At a special angle known as Brewster's angle, no p- polarized light is reflected from the surface, thus all reflected light must be s- polarized, with an electric field perpendicular to the plane of incidence. For simple glass plates at Brewster’s angle about 16% of the s-polarized light present in the beam is reflected for each air-to-glass or glass-to-air transition. For angles of incidence steeper than 80° the polarization of the transmitted beam can approach 100% with as few as four plates.
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Birefringent polarizers
Other linear polarizers exploit the birefringent properties of crystals such as quartz and calcite. A Nicol prism was an early type of birefringent polarizer, that consists of a crystal of calcite which has been split and rejoined with Canada balsam. The crystal is cut such that the o- and e-rays are in orthogonal linear polarization states. Other examples are Wallston prism, Nomarski prism. Thin-film linear polarizers are glass substrates
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which a special optical coating is applied. Interference effects in the film cause them to act as beam- splitting polarizers.
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Circular polarizers
Thin-film linear polarizers are glass substrates on which a special optical coating is applied. Interference effects in the film cause them to act as beam- splitting polarizers. Half wave plate
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Quarter wave plate
Circular polarizers
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Circular polarizer setup
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1. LASERS 2. DIC microscopy and other microscopic techniques. 3. Liquid crystal display 4. Photography 5. 3D glasses.
Applications
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Plasmonic Imaging of Brownian Motion of Single DNA Molecules Spontaneously Binding to Ag Nanoparticles Nano Lett. dx.doi.org/10.1021/nl304247n
By - Kamalesh 19-04-2013
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