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.

Patent

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 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 can't 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.

Building Seen Through Polaroid Sunglasses
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]

Applications

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.

References

  1. ^ U.S. Patent 1,918,848
  2. ^ U.S. Patent 2,237,567
  3. ^ U.S. Patent 5,666,223
  • Land, E.H. (1951). "Some aspects on the development of sheet polarizers". J. Optical Society of America 41 (12), 957-963.
  • Halliday, Resnick, Walker. "Fundamentals of Physics" 7th edition. John Wiley & Sons, Inc.

External links

Index of optics articles

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

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The index of physics articles is split into multiple pages due to its size.

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Polarization (waves)

Polarization (also polarisation) is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a taut string (see image); for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids. In some types of transverse waves, the wave displacement is limited to a single direction, so these also do not exhibit polarization; for example, in surface waves in liquids (gravity waves), the wave displacement of the particles is always in a vertical plane.

An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular; by convention, the "polarization" of electromagnetic waves refers to the direction of the electric field. In linear polarization, the fields oscillate in a single direction. In circular or elliptical polarization, the fields rotate at a constant rate in a plane as the wave travels. The rotation can have two possible directions; if the fields rotate in a right hand sense with respect to the direction of wave travel, it is called right circular polarization, or, if the fields rotate in a left hand sense, it is called left circular polarization.

Light or other electromagnetic radiation from many sources, such as the sun, flames, and incandescent lamps, consists of short wave trains with an equal mixture of polarizations; this is called unpolarized light. Polarized light can be produced by passing unpolarized light through a polarizer, which allows waves of only one polarization to pass through. The most common optical materials (such as glass) are isotropic and do not affect the polarization of light passing through them; however, some materials—those that exhibit birefringence, dichroism, or optical activity—can change the polarization of light. Some of these are used to make polarizing filters. Light is also partially polarized when it reflects from a surface.

According to quantum mechanics, electromagnetic waves can also be viewed as streams of particles called photons. When viewed in this way, the polarization of an electromagnetic wave is determined by a quantum mechanical property of photons called their spin. A photon has one of two possible spins: it can either spin in a right hand sense or a left hand sense about its direction of travel. Circularly polarized electromagnetic waves are composed of photons with only one type of spin, either right- or left-hand. Linearly polarized waves consist of photons that are in a superposition of right and left circularly polarized states, with equal amplitude and phases synchronized to give oscillation in a plane.Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology, radio, and microwaves. Especially impacted are technologies such as lasers, wireless and optical fiber telecommunications, and radar.

Polaroid

Polaroid may refer to:

Polaroid Corporation, an American worldwide consumer electronics and eyewear company, and former instant camera and film maker

Polaroid camera, or instant camera

Polaroid film, instant film and photographs

Polaroid Originals, a Dutch manufacturer of instant film and cameras, owner of Polaroid Corporation's brand and intellectual property

Polaroid (polarizer), a type of synthetic plastic sheet used to polarize light

Polaroid Eyewear, with glare-reducing polarized lenses made from Polaroid's polarizer

Polaroid Corporation

Polaroid is an American company that is a brand licensor and marketer of its portfolio of consumer electronics to companies that distribute consumer electronics and eyewear. It is best known for its Polaroid instant film and cameras. In 2017, its parent company was acquired by Polish investor Oskar Smołokowski.

The company was founded in 1937 by Edwin H. Land, to exploit the use of its Polaroid polarizing polymer. Land ran the company until 1981. Its peak employment was 21,000 in 1978, and its peak revenue was $3 billion in 1991.When the original Polaroid Corporation was declared bankrupt in 2001, its brand and assets were sold off. The "new" Polaroid formed as a result, and itself declared bankruptcy in 2008, resulting in a further sale and in the present-day Polaroid Corporation. In May 2017, the brand and intellectual property of the Polaroid corporation were acquired by the largest shareholder of the Impossible Project, which had originally started out in 2008 by producing new instant films for Polaroid cameras. The Impossible Project was renamed Polaroid Originals in September 2017.

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