Polaroid (polarizer)

Polaroid is a type of synthetic plastic sheet which is used as a polarizer or polarizing filter. A trademark of the Polaroid Corporation, the term has since entered common use.

The original material, patented in 1929[1] and further developed in 1932 by Edwin H. Land, consists of many microscopic crystals of iodoquinine sulphate (herapathite) embedded in a transparent nitrocellulose polymer film. The needle-like crystals are aligned during the manufacture of the film by stretching or by applying electric or magnetic fields. With the crystals aligned, the sheet is dichroic: it tends to absorb light which is polarized parallel to the direction of crystal alignment but to transmit light which is polarized perpendicular to it.
The resultant electric field of an electromagnetic wave (such as light) determines its polarization. If the wave interacts with a line of crystals as in a sheet of polaroid, any varying electric field in the direction parallel to the line of the crystals will cause a current to flow along this line. The electrons moving in this current will collide with other particles and re-emit the light backwards and forwards. This will cancel the incident wave causing little or no transmission through the sheet.
The component of the electric field perpendicular to the line of crystals, however, can cause only small movements in the electrons as they cannot move very much from side to side. This means there will be little change in the perpendicular component of the field leading to transmission of the part of the light wave polarized perpendicular to the crystals only, hence allowing the material to be used as a light polarizer.[citation needed]

A building seen through polaroid sunglasses
This material, known as J-sheet, was later replaced by the improved H-sheet Polaroid, invented in 1938 by Land. H-sheet is a polyvinyl alcohol (PVA) polymer impregnated with iodine. During manufacture, the PVA polymer chains are stretched such that they form an array of aligned, linear molecules in the material. The iodine dopant attaches to the PVA molecules and makes them conducting along the length of the chains. Light polarized parallel to the chains is absorbed, and light polarized perpendicular to the chains is transmitted.[2]
Another type of Polaroid is the K-sheet polarizer, which consists of aligned polyvinylene chains in a PVA polymer created by dehydrating PVA. This polarizer material is particularly resistant to humidity and heat.[3]

Polarizing sheets are used in liquid-crystal displays, optical microscopes and sunglasses. Since Polaroid sheet is dichroic, it will absorb impinging light of one plane of polarization, so sunglasses will reduce the partially polarized light reflected from level surfaces such as windows and sheets of water, for example. They are also used to examine for chain orientation in transparent plastic products made from polystyrene or polycarbonate.
The intensity of light passing through a Polaroid polarizer is described by Malus' law.

^ U.S. patent 1,918,848

^ U.S. patent 2,237,567

^ U.S. patent 5,666,223

Edwin H. Land (1951). "Some aspects on the development of sheet polarizers". Journal of the Optical Society of America 41(12): 957–963.
Halliday, Resnick, Walker. Fundamentals of Physics, 7th edition, John Wiley & Sons
William Shurcliff (1962). Polarized Light: Production and Use, Harvard University Press.

"One-Way Glass Stops Glare" Popular Mechanics, April 1936 pp. 481-483

🔐 Cryptographic Verification

�� CONTENT HASHES: SHA-256: d88b2afb4f8e4445a8498e7264daa8bd5e596b9ad008976dcd803959efc22962 BLAKE2b: 2dbb1b84be0bfa89e72c470e65efc4839045a65c8cc1ee4d3310016da100264d MD5: 8d66c35b8e4503b2bd6a55698335856e �� TITLE HASHES: SHA-256: 0c17a88659d42de2ab98e1221ea94df3ae8bc8cee0b772dc541c28a7398eb623 BLAKE2b: 03354562f739889cb8909deaf90fcdd0b4f209f3d50ff676c2b5b79bb72e1923 MD5: 99494a93ea6224db1dead8324f1613e1 �� INTEGRITY HASHES: SHA-256: 9ede60b20459c824eb5dbf96a261759a8e402065550ffc491de95f1e21d5cac4 BLAKE2b: adf868ef821c23a3fe647d29c3eb1c4f160970fad6dfdd5e82913e78bd2a73f0 MD5: 1b88202b2c10dc358e805ccb2f8abf53

Archived with ArcHive - Client-side cryptographic archival system