Polaroid filter

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Polaroid filters comprise a group of polarizing filters that were developed and sold by Edwin Herbert Land and employees of the Polaroid company in the 20th century. The name “Polaroid” goes back to polarizers whose thickness perpendicular to the direction of propagation of the light is much smaller than their width. The polarizing foils ( English sheet polarizer ), foils with a polarizing effect , are distinguished from the polarizers used up to then mainly by a cost-effective production. Such filters are mainly used in photography .

J foils

J-foils (engl. J-sheet ) were the first polarizing foils developed by Edwin Herbert Land (1929). They are made of dichroic herapathite - crystallites , in a film of cellulose are embedded. The polarizing effect of the foils is based on the parallel arrangement of the submicrometer-sized needle-shaped crystallites and their polarization-dependent absorption (dichroism). Since the size of the crystallites is in the range of the wavelength of visible light and therefore scatters the light, J-foils generally look somewhat cloudy .

H-foils

H-foils (engl. H-sheet ) are one of the most widely used polarization foils . They were first presented in 1938 by Edwin H. Land and consist of a colorless polyvinyl alcohol (PVA) film with incorporated iodine . Land achieved directional polarization by first heating the PVA film and stretching it in a certain direction . As a result, the long-chain polymers were aligned in parallel. When the iodine crystallites were then introduced, they were deposited on the PVA molecules and in turn formed long, electrically conductive chains. The one diffused iodine provides charge carriers that are mobile in the direction of the chain molecules, which leads to the absorption of the parallel component of the electric field . The H-foils therefore function like the metallic grid of a wire grid polarizer . Since the deposited iodine crystallites are only a few nanometers in size, the scattering of the H-foils is negligible; unlike the J-foils, they do not appear cloudy.

K foils

The K-foils (engl. K-sheet ) are produced - similar to the H-foils - by heating a polyvinyl alcohol foil in the presence of a catalyst . The heating is used to remove water and produce di- chromophoric polyvinyl . They are particularly suitable for applications that require greater resistance to elevated temperatures and high humidity . Similar to H-foils, they show no clouding.

There are also combinations of H and K foils, the absorption maximum of which is around 1.5 µm in the infrared . They are known as the HR Polaroid.

literature

  • Michael Bass (Ed.): Handbook of Optics, Third Edition Volume I: Geometrical and Physical Optics, Polarized Light, Components and Instruments . McGraw-Hill Professional, 2009, p. 13.25–13.27 (contains the transmission spectra of the filters).
  • Edwin H. Land: Some Aspects of the Development of Sheet Polarizers . In: Journal of the Optical Society of America . tape 41 , no. 12 , 1951, pp. 957-962 , doi : 10.1364 / JOSA.41.000957 .
  • Erik W. Thulstrup, Josef Michl: Elementary Polarization Spectroscopy . John Wiley and Sons, 1989, ISBN 978-0-471-19057-8 , pp. 1-3 .

Individual evidence

  1. ↑ Patent US1918848 : Polarizing refracting bodies. Registered April 26, 1929 , published July 18, 1933 , inventor: Edwin H. Land. ‌
  2. ^ State of polarization of light (PDF; 305 kB). Faculty of Physics and Astronomy, Friedrich Schiller University Jena, p. 5.