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 01

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. 02

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 03

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. 04

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 on which a special optical coating is applied. Interference effects in the film cause them to act as beam- splitting polarizers. 05

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 06

Circular polarizers Quarter wave plate 07

Circular polarizer setup 08

Applications 1. LASERS 2. DIC microscopy and other microscopic techniques. 3. Liquid crystal display 4. Photography 5. 3D glasses. 09

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

01

02

03

04

Thank you