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Encyclopedia > Slow light
Refractive phenomena, such as this rainbow, are due to the slower speed of light in a medium (water, in this case).

Slow light is the literal slowing of the speed of light. It is the propagation of an optical pulse or other modulation of an optical carrier at a very low group velocity. The term is usually only applied when the velocity is at least hundreds of times slower than the speed of light in a vacuum. Image File history File links Supernumerary_rainbow_03_contrast. ... Image File history File links Supernumerary_rainbow_03_contrast. ... The straw seems to be broken, due to refraction of light as it emerges into the air. ... For other uses, see Rainbow (disambiguation). ... â€œLightspeedâ€ redirects here. ... The group velocity of a wave is the velocity with which the variations in the shape of the waves amplitude (known as the modulation or envelope of the wave) propagate through space. ...

Researchers at UC Berkeley slowed the speed of light traveling through a semiconductor to 6 miles per second in 2004. This was in an effort to develop computers that will use only a fraction of the energy of today's machines.[1]
The University of California, Berkeley (also known as Cal, UC Berkeley, UCB, or simply Berkeley) is a prestigious, public, coeducational university situated in the foothills of Berkeley, California to the east of San Francisco Bay, overlooking the Golden Gate and its bridge. ... A semiconductor is a solid whose electrical conductivity is in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ...

In 2005, IBM created a microchip that can slow down light, claiming that its light-slowing device is the first to be fashioned out of fairly standard materials, potentially paving the way toward commercial adoption.[2] For other uses, see IBM (disambiguation) and Big Blue. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ...

## Contents

While the speed of light in a vacuum is a well-known physical constant, when light is subject to physical conditions other than a vacuum, the effective velocity of the electromagnetic waves that make up the light can change. The most well-known instance of this is when light is transmitted through a refractive material that has an electric permittivity and a magnetic permeability different from a vacuum. When this occurs the index of refraction can be determined for a material as follows: â€œLightspeedâ€ redirects here. ... Look up Vacuum in Wiktionary, the free dictionary. ... In physics, a physical constant is a physical quantity of a value that is generally believed to be both universal in nature and not believed to change in time. ... Electromagnetic radiation is a propagating wave in space with electric and magnetic components. ... The straw seems to be broken, due to refraction of light as it emerges into the air. ... Permittivity is a physical quantity that describes how an electric field affects and is affected by a medium. ... This article is in need of attention. ... The refractive index of a material is the factor by which electromagnetic radiation is slowed down (relative to vacuum) when it travels inside the material. ...

n = c / v

where n is the index of refraction, c is the speed of light in a vacuum, and v is the apparent speed of light through the material. As the index of refraction increases, the observed speed of light in the medium decreases. Theoretically, there is no limit to the index of refraction, and it is possible to obtain values for n that approach infinity. When this happens, the speed of light in the material becomes effectively equal to zero, and light has "stopped moving". The infinity symbol âˆž in several typefaces. ...

Microphysically, in the quantum mechanical view, photons of light are interacting through a lattice arrangement of atoms in a material either through repeating processes of absorption and re-emission, or by many different scattering processes. In the case of absorption and re-emission, there is a finite amount of time for a material to absorb and re-emit a photon, this lag time will cause an effective "slowing" of the observed photon speed, even though when between absorptions and re-emissions the photon is traveling at c. For scattering processes, the photon takes a path that is a longer distance than the metric displacement along its trajectory. As the photon is scattered, it follows a circuitous path which is constantly changing direction but on average is propagating in a straight-line direction. This also has the effect of appearing to slow down the speed of light since the photons are traveling the speed of light along a longer distance. Fig. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... For other uses, see Atom (disambiguation). ... In physics, absorption is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. ... In physics, emission is the process by which the energy of a photon is released by another entity, for example, by an atom whose valence electrons make a transition between two electronic energy levels. ... Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ... In Newtonian mechanics, displacement is the vector that specifies the position of a point or a particle in reference to an origin or to a previous position. ...

## Procedure

There are many mechanisms which can generate slow light, all of which create narrow spectral regions with high dispersion, i.e. peaks in the dispersion relation. Schemes are generally grouped into two categories: material dispersion and waveguide dispersion. Material dispersion mechanisms such as Electromagnetically Induced Transparency (EIT), Coherent Population Oscillation (CPO), and various Four Wave Mixing (FWM) schemes produce a rapid change in refractive index as a function of optical frequency, i.e. they modify the temporal component of a propagating wave. This is done by using a nonlinear effect to modify the dipole response of a medium to a signal or "probe" field. Waveguide dispersion mechanisms such as photonic crystals, Coupled Resonator Optical Waveguides (CROW), and other micro-resonator structures modify the spatial component (k-vector) of a propagating wave. Dispersion of a light beam in a prism. ... The relation between the energy of a system and its corresponding momentum is known as its dispersion relation. ... The effect of EIT on a typical absorption line. ... Four Wave Mixing is an intermodulation distortion in optical systems, similar to the third order intercept in electrical systems. ... The opal in this bracelet contains a natural periodic microstructure responsible for its iridescent color. ...

A predominant figure of merit of slow light schemes is the Delay-Bandwidth Product (DBP). Most slow light schemes can actually offer an arbitrarily long delay for a given device length (length/delay = signal velocity) at the expense of bandwidth. The product of the two is roughly constant. A related figure of merit is the fractional delay, the time a pulse is delayed divided by the total time of the pulse.-1...

## Potential use

Slow light could be used to greatly reduce noise, which could allow all types of information to be transmitted more efficiently. Also, optical switches controlled by slow light could cut power requirements a million-fold compared to switches now operating everything from telephone equipment to supercomputers. [3] Slowing light could lead to a more orderly traffic flow in networks. For the Irish mythological figure, see Naoise. ... In telecommunications, transmission is the act of transmitting electrical messages (and the associated phenomena of radiant energy that passes through media). ... This article or section is in need of attention from an expert on the subject. ...

## Slow light in fiction

Slow glass is a fictional material in Bob Shaw's short story "Light of other days" (Analog, 1966). The glass, which delays the passage of light by years or decades, is used to construct windows, called scenedows, that enable city dwellers, submariners and prisoners to watch "live" countryside scenes. The delay light takes in passing through the glass is attributed to photons passing "...through a spiral tunnel coiled outside the radius of capture of each atom in the glass.". Bob Shaw later reworked the idea in the novel Other Days, Other Eyes (1972). Fictional chemical substances are compounds or minerals that exist only in works of fiction (usually fantasy or science fiction). ... Bob Shaw (December 31, 1931 - February 12, 1996) was a British science fiction author and fan. ... April 1997 issue of Analog. ...

Slow glass also appears in Unknown Worlds Of Science Fiction comics (1975). In these stories, the glass originates in the future, and its ability to show "...scenes from various locations in time, space and other dimensions..." is used as a framing device for the comic's stories. It use was directly inspired by Bob Shaw's story.[4]

The slow light experiments are mentioned in Dave Eggers' novel You Shall Know Our Velocity!. In the novel, the speed of light is described as a "sunday crawl". Dave Eggers at the 2005 Hay Festival Dave Eggers (born March 12, 1970) is an American writer, editor, and publisher. ... You Shall Know Our Velocity (or YSKOV) is a fiction novel written by Dave Eggers, published in hardcover in San Francisco, California by McSweeneys in 2002 with ISBN 0970335555, and later in paperback in New York by Vintage in 2003 with ISBN 1400033543. ...

On Discworld, where Terry Prattchet's novel series takes place, light travels only a few hundred miles per hour due to Discworld's high magic field. Cover of an early edition of The Colour of Magic; art by Josh Kirby Discworld is a comedic fantasy book series by the British author Terry Pratchett set on the Discworld, a flat world balanced on the backs of four elephants which are in turn standing on the back of... Terence David John Pratchett OBE (born 28 April 1948, in Beaconsfield, Buckinghamshire, England)[1] is an English fantasy author, best known for his Discworld series. ...

## References

• Lene Vestergaard Hau, S.E. Harris, Zachary Dutton, Cyrus H. Behroozi, Nature v.397, p.594 (1999).
• "IBM's new photonic wave-guide". Nature, November 2004.
• ^ Harvard.edu

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