terahertz

Electromagnetic waves sent at terahertz frequencies, known as terahertz radiation, terahertz waves, terahertz light, T-rays, T-light, T-lux and THz, are in the region of the electromagnetic spectrum between 300 gigahertz (3x1011 Hz) and 3 terahertz (3x1012 Hz), corresponding to the submillimeter wavelength range between 1 millimeter (high-frequency edge of the microwave band) and 100 micrometres (long-wavelength edge of far-infrared light).

Enlarge picture
Plot of the zenith atmospheric transmission on the summit of Mauna Kea throughout the range of 1 to 3 THz of the electromagnetic spectrum at a precipitable water vapor level of 0.001 mm. (simulated)

Introduction

Like infrared radiation or microwaves, these waves usually travel in line of sight. Terahertz radiation is non-ionizing and shares with microwaves the capability to penetrate a wide variety of non-conducting materials. They can pass through clothing, paper, cardboard, wood, masonry, plastic and ceramics. They can also penetrate fog and clouds but cannot penetrate metal or water.

The Earth's atmosphere is a strong absorber of terahertz radiation, so the range of terahertz radiation is quite short, limiting its usefulness. In addition, producing and detecting coherent terahertz radiation was technically challenging until the 1990s.

Sources

While terahertz radiation is emitted as part of the black body radiation from anything with temperatures greater than about 10 kelvin, this thermal emission is very weak. As of 2004 the only effective stronger sources of terahertz radiation are the gyrotron, the backward wave oscillator ("BWO"), the far infrared laser ("FIR laser"), quantum cascade laser, the free electron laser (FEL), synchrotron light sources, and single-cycle sources used in Terahertz time domain spectroscopy. The first images generated using terahertz radiation date from the 1960's; however, in 1995, images generated using terahertz time-domain spectroscopy generated a great deal of interest, and sparked a rapid growth in the field of terahertz science and technology. This excitement, along with the associated coining of the term "T-rays," even showed up in a contemporary novel by Tom Clancy.

There have also been solid-state sources of millimeter and submillimeter waves for many years. AB Millimeter in Paris, for instance, produces a system that covers the entire range from 8 GHz to 1000 GHz with solid state sources and detectors. Nowadays, most time-domain work is done via ultrafast lasers.

Theoretical and technological uses under development

  • Medical imaging:
  • Terahertz radiation is non-ionizing, and thus is not expected to damage tissues and DNA, unlike X-rays. Some frequencies of terahertz radiation can penetrate several millimeters of tissue with low water content (e.g. fatty tissue) and reflect back. Terahertz radiation can also detect differences in water content and density of a tissue. Such methods could allow effective detection of epithelial cancer with a safer and less invasive or painful system using imaging.
  • Some frequencies of terahertz radiation can be used for 3D imaging of teeth and may be more accurate and safer than conventional X-ray imaging in dentistry.
  • Security:
  • Terahertz radiation can penetrate fabrics and plastics, so it can be used in surveillance, such as security screening, to uncover concealed weapons on a person, remotely. This is of particular interest because many materials of interest, such as plastic explosives, have unique spectral fingerprints in the terahertz range. This offers the possibility to combine spectral identification with imaging. Some controversy surrounds the privacy issues in using terahertz scanners for routine security checks due to the ability to produce detailed images of a subject's body through clothing, though this method is less invasive than a strip search.
  • Scientific use and imaging:
  • Spectroscopy in terahertz radiation could provide novel information in chemistry and biochemistry.
  • Recently developed methods of THz time-domain spectroscopy (THz TDS) and THz tomography have been shown to be able to perform measurements on, and obtain images of, samples which are opaque in the visible and near-infrared regions of the spectrum. The utility of THz-TDS is limited when the sample is very thin, or has a low absorbance, since it is very difficult to distinguish changes in the THz pulse caused by the sample from those caused by long term fluctuations in the driving laser source or experiment. However, THz-TDS produces radiation that is both coherent and broadband, so such images can contain far more information than a conventional image formed with a single-frequency source.
  • A primary use of submillimeter waves in physics is the study of condensed matter in high magnetic fields, since at high fields (over about 15 Tesla), the Larmor frequencies are in the submillimeter band. This work is performed at many high-magnetic field laboratories around the world.
  • A fast growing use is in millimeter/submillimeter wave astronomy.
  • Communication:
  • Potential uses exist in high-altitude telecommunications, above altitudes where water vapor causes signal absorption: aircraft to satellite, or satellite to satellite.
  • Manufacturing:
  • Many possible uses of terahertz sensing and imaging are proposed in manufacturing, quality control, and process monitoring. These generally exploit the traits of plastics and cardboard being transparent to terahertz radiation, making it possible to inspect packaged goods.

Terahertz versus submillimeter waves

The terahertz band, covering the wavelength range between 0.1 and 1 mm, is similar to the submillimeter wavelength band. However, typically, the term "terahertz" is used more often in relation to generation and detection with pulsed lasers, as in terahertz time domain spectroscopy, while the term "submillimeter" is used for generation and detection with microwave technology, such as harmonic multiplication.

References

Books on millimeter and submillimeter waves and RF optics

See also

External links

T-ray can signify:
  • Terahertz radiation
  • T-Ray (comics), a fictional character.
  • T-Ray (producer): Todd Ray, a producer who has worked with Cypress Hill, G. Love and Special Sauce and Helmet among others.

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Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other.
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terahertz radiation, terahertz waves, terahertz light, T-rays, T-light, T-lux and THz, are in the region of the electromagnetic spectrum between 300 gigahertz (3x1011 Hz) and 3 terahertz (3x1012
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FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. A sequel, titled Amplitude was released in 2003.
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electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. The "electromagnetic spectrum" (usually just spectrum) of an object is the frequency range of electromagnetic radiation with wavelengths from thousands of kilometers down to fractions of
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hertz (symbol: Hz) is the SI unit of frequency. Its base unit is cycle/s or s-1 (also called inverse seconds, reciprocal seconds). In English, hertz is used as both singular and plural.
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hertz (symbol: Hz) is the SI unit of frequency. Its base unit is cycle/s or s-1 (also called inverse seconds, reciprocal seconds). In English, hertz is used as both singular and plural.
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terahertz radiation, terahertz waves, terahertz light, T-rays, T-light, T-lux and THz, are in the region of the electromagnetic spectrum between 300 gigahertz (3x1011 Hz) and 3 terahertz (3x1012
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In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenonomena are light, water waves, and sound waves.
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1 millimetre =
SI units
010−3 m 0 cm
US customary / Imperial units
010−3 ft 010−3 in
The millimetre (American spelling: millimeter, symbol mm
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Microwaves are electromagnetic waves with wavelengths shorter than one meter and longer than one millimeter, or frequencies between 300 megahertz and 300 gigahertz.
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1 micrometre =
SI units
010−6 m 010−3 mm
US customary / Imperial units
010−6 ft 010−6 in
A micrometre (American spelling: micrometer; symbol µm
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Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. The name means "below red" (from the Latin infra, "below"), red being the color of visible light with the longest wavelength.
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Light is electromagnetic radiation of a wavelength that is visible to the eye (visible light). In a scientific context, the word "light" is sometimes used to refer to the entire electromagnetic spectrum.
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Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. The name means "below red" (from the Latin infra, "below"), red being the color of visible light with the longest wavelength.
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Microwaves are electromagnetic waves with wavelengths shorter than one meter and longer than one millimeter, or frequencies between 300 megahertz and 300 gigahertz.
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Line-of-sight propagation refers to electro-magnetic radiation travelling in a straight line. The rays are therefore deviated or reflected by obstructions and cannot travel over the horizon. Beyond that, material disperses the rays.
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Ionizing radiation is energetic particles or waves that have the potential to ionize an atom or molecule through atomic interactions. It is a function of the energy of the individual particles or waves, and not a function of the number of particles or waves present.
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In science and engineering, conductors, such as copper or aluminum, are materials with atoms have loosely held valence electrons. See electrical conduction.

Conductors in context


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original research or unverifiable claims.
* It may contain an of published material that conveys ideas not verifiable with the given sources. Please help add reliable sources about the topic "August 2007."
* It does not cite any references or sources.
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Paper is thin material used for writing upon, printing upon or packaging, produced by the amalgamation of fibres, typically vegetable fibers composed of cellulose, which are subsequently held together by hydrogen bonding.
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Cardboard is a generic non-specific term for a heavy duty paper based product.

Paperboard

Main article: Paperboard


Paperboard is a paper based material.
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The WOOD callsign may refer to:
  • WOOD-TV – an NBC-affiliated television station in Grand Rapids, Michigan
  • WOOD (AM) – an AM radio station in Grand Rapids, Michigan
  • WOOD-FM - an FM radio station in Grand Rapids, Michigan




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Masonry is the building of structures from individual units laid in and bound together by mortar (though the word "masonry" sometimes means the stones, rather than the act or art of building, particularly in the expression "falling masonry" used in reports of fires and earthquakes).
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Plastic is the general term for a wide range of synthetic or semisynthetic polymerization products. They are composed of organic condensation or addition polymers and may contain other substances to improve performance or economics.
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ceramic is derived from the Greek word κεραμικός (keramikos). The term covers inorganic non-metallic materials which are formed by the action of heat.
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FOG can be an acronym for...
  • the tool "Flexible Object Generator"
  • the tool "Fragmented-Object Generator"
  • Fiber Optic Gulf - a submarine telecommunications cable linking the United Arab Emirates, Qatar, Bahrain, and Kuwait
  • Fibre optic gyroscope

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cloud is a visible mass of condensed droplets, frozen crystals suspended in the atmosphere above the surface of the Earth or another planetary body, such as a moon. (Clouds can also occur as masses of material in interstellar space, where they are called interstellar clouds and
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The Macro Expansion Template Attribute Language complements TAL, providing macros which allow the reuse of code across template files. Both were created for Zope but are used in other Python projects as well.
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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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