Terahertz radiation

Last updated

Tremendously high frequency
Frequency range
300 GHz to 3 THz
Wavelength range
1 mm to 100 μm
Terahertz waves lie at the far end of the infrared band, just before the start of the microwave band. Spectre Terahertz.svg
Terahertz waves lie at the far end of the infrared band, just before the start of the microwave band.

Terahertz radiation also known as submillimeter radiation, terahertz waves, tremendously high frequency [1] (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3  terahertz (THz). One terahertz is 1012  Hz or 1000 GHz. Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm (or 100  μm). Because terahertz radiation begins at a wavelength of one millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy.

Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

Hertz SI unit for frequency

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), terahertz (1012 Hz, THz), petahertz (1015 Hz, PHz), and exahertz (1018 Hz, EHz).

Micro- prefix denoting 10 to the −6th power

Micro- is a unit prefix in the metric system denoting a factor of 10−6. Confirmed in 1960, the prefix comes from the Greek μικρός, meaning "small".

Contents

Terahertz radiation can penetrate thin layers of materials but is blocked by thicker objects. THz beams transmitted through materials can be used for material characterization, layer inspection, and as an alternative to X-rays for producing high resolution images of the interior of solid objects. [2]

Characterization (materials science) process by which a materials structure and properties are probed and measured

Characterization, when used in materials science, refers to the broad and general process by which a material's structure and properties are probed and measured. It is a fundamental process in the field of materials science, without which no scientific understanding of engineering materials could be ascertained. The scope of the term often differs; some definitions limit the term's use to techniques which study the microscopic structure and properties of materials, while others use the term to refer to any materials analysis process including macroscopic techniques such as mechanical testing, thermal analysis and density calculation. The scale of the structures observed in materials characterization ranges from angstroms, such as in the imaging of individual atoms and chemical bonds, up to centimeters, such as in the imaging of coarse grain structures in metals.

X-ray form of electromagnetic radiation

X-rays make up X-radiation, a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to with terms meaning Röntgen radiation, after the German scientist Wilhelm Röntgen who discovered these on November 8, 1895, who usually is credited as its discoverer, and who named it X-radiation to signify an unknown type of radiation. Spelling of X-ray(s) in the English language includes the variants x-ray(s), xray(s), and X ray(s).

Terahertz radiation occupies a middle ground between microwaves and infrared light waves known as the “terahertz gap”, where technology for its generation and manipulation is in its infancy. It represents the region in the electromagnetic spectrum where the frequency of electromagnetic radiation becomes too high to be measured digitally via electronic counters, so must be measured by proxy using the properties of wavelength and energy. Similarly, the generation and modulation of coherent electromagnetic signals in this frequency range ceases to be possible by the conventional electronic devices used to generate radio waves and microwaves, requiring the development of new devices and techniques.

Microwave form of electromagnetic radiation

Microwaves are a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter; with frequencies between 300 MHz (1 m) and 300 GHz (1 mm). Different sources define different frequency ranges as microwaves; the above broad definition includes both UHF and EHF bands. A more common definition in radio engineering is the range between 1 and 100 GHz. In all cases, microwaves include the entire SHF band at minimum. Frequencies in the microwave range are often referred to by their IEEE radar band designations: S, C, X, Ku, K, or Ka band, or by similar NATO or EU designations.

Terahertz gap is an engineering term for a frequency band in the terahertz region of the electromagnetic spectrum between radio waves and infrared light for which practical technologies for generating and detecting the radiation do not exist. It is defined as 0.1 to 10 THz. Currently, at frequencies within this range, useful power generation and receiver technologies are inefficient and impractical.

The electromagnetic spectrum is the range of frequencies of electromagnetic radiation and their respective wavelengths and photon energies.

Introduction

In THz-TDS systems, since the time-domain version of the THz signal is available, the distortion effects of the diffraction can be suppressed. Resolution Enhancement.gif
In THz-TDS systems, since the time-domain version of the THz signal is available, the distortion effects of the diffraction can be suppressed.

Terahertz radiation falls in between infrared radiation and microwave radiation in the electromagnetic spectrum, and it shares some properties with each of these. Like infrared and microwave radiation, terahertz radiation travels in a line of sight and is non-ionizing. Like microwave radiation, terahertz radiation can penetrate a wide variety of non-conducting materials. Terahertz radiation can pass through clothing, paper, cardboard, wood, masonry, plastic and ceramics. The penetration depth is typically less than that of microwave radiation. Terahertz radiation has limited penetration through fog and clouds and cannot penetrate liquid water or metal. [4] Terahertz radiation is not ionizing yet can penetrate some distance through body tissue, so it is of interest as a replacement for medical X-rays. Due to its longer wavelength, images made using terahertz waves have lower resolution than X-rays and need to be enhanced (see figure at right) [3] .

Non-ionizing radiation electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules

Non-ionizingradiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule. Instead of producing charged ions when passing through matter, non-ionizing electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Ionizing radiation which has a higher frequency and shorter wavelength than nonionizing radiation, has many uses but can be a health hazard; exposure to it can cause burns, radiation sickness, cancer, and genetic damage. Using ionizing radiation requires elaborate radiological protection measures which in general are not required with nonionizing radiation.

Insulator (electricity) material whose internal electric charges do not flow freely, and which therefore does not conduct an electric current

An electrical insulator is a material whose internal electric charges do not flow freely; very little electric current will flow through it under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.

Paperboard thick paper-based material

Paperboard is a thick paper-based material. While there is no rigid differentiation between paper and paperboard, paperboard is generally thicker than paper and has certain superior attributes such as foldability and rigidity. According to ISO standards, paperboard is a paper with a grammage above 250 g/m2, but there are exceptions. Paperboard can be single- or multi-ply.

The earth's atmosphere is a strong absorber of terahertz radiation, so the range of terahertz radiation in air is limited to tens of meters, making it unsuitable for long-distance communications. However, at distances of ~10 meters the band may still allow many useful applications in imaging and construction of high bandwidth wireless networking systems, especially indoor systems. In addition, producing and detecting coherent terahertz radiation remains technically challenging, though inexpensive commercial sources now exist in the 0.31.0 THz range (the lower part of the spectrum), including gyrotrons, backward wave oscillators, and resonant-tunneling diodes.

Wireless network any network at least partly not connected by physical cables of any kind

A wireless network is a computer network that uses wireless data connections between network nodes.

In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. Coherence is an ideal property of waves that enables stationary interference. It contains several distinct concepts, which are limiting cases that never quite occur in reality but allow an understanding of the physics of waves, and has become a very important concept in quantum physics. More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets.

Gyrotron

A gyrotron is a class of high-power linear-beam vacuum tubes which generates millimeter-wave electromagnetic waves by the cyclotron resonance of electrons in a strong magnetic field. Output frequencies range from about 20 to 527 GHz, covering wavelengths from microwave to the edge of the terahertz gap. Typical output powers range from tens of kilowatts to 1–2 megawatts. Gyrotrons can be designed for pulsed or continuous operation.

Terahertz versus submillimeter waves

The terahertz band, covering the wavelength range between 0.11 mm, is identical to the submillimeter wavelength band. However, typically, the term "terahertz" is used more often in marketing 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.[ citation needed ]

Sources

Natural

Terahertz radiation is emitted as part of the black-body radiation from anything with a temperature greater than about 2  Kelvin. While this thermal emission is very weak, observations at these frequencies are important for characterizing cold 1020  K cosmic dust in interstellar clouds in the Milky Way galaxy, and in distant starburst galaxies.

Telescopes operating in this band include the James Clerk Maxwell Telescope, the Caltech Submillimeter Observatory and the Submillimeter Array at the Mauna Kea Observatory in Hawaii, the BLAST balloon borne telescope, the Herschel Space Observatory, the Heinrich Hertz Submillimeter Telescope at the Mount Graham International Observatory in Arizona, and at the recently built Atacama Large Millimeter Array. The opacity of the Earth's atmosphere to submillimeter radiation restricts these observatories to very high altitude sites, or to space.

Artificial

As of 2012, viable sources of terahertz radiation are the gyrotron, the backward wave oscillator ("BWO"), the organic gas far infrared laser ("FIR laser"), Schottky diode multipliers, [5] varactor (varicap) multipliers, quantum cascade laser, [6] [7] [8] [9] the free electron laser (FEL), synchrotron light sources, photomixing sources, single-cycle or pulsed sources used in terahertz time domain spectroscopy such as photoconductive, surface field, photo-Dember and optical rectification emitters, [10] and electronic oscillators based on resonant tunneling diodes have been shown to operate up to 700 GHz. [11]

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.

In mid-2007, scientists at the U.S. Department of Energy's Argonne National Laboratory, along with collaborators in Turkey and Japan, announced the creation of a compact device that could lead to portable, battery-operated terahertz radiation sources. [12] The device uses high-temperature superconducting crystals, grown at the University of Tsukuba in Japan. These crystals comprise stacks of Josephson junctions, which exhibit a property known as the Josephson effect—when external voltage is applied, alternating current flows across the junctions at a frequency proportional to the voltage. This alternating current induces an electromagnetic field. A small voltage (around two millivolts per junction) can induce frequencies in the terahertz range.

In 2008 engineers at Harvard University achieved room temperature emission of several hundred nanowatts of coherent terahertz radiation using a semiconductor source. THz radiation was generated by nonlinear mixing of two modes in a mid-infrared quantum cascade laser. Previous sources had required cryogenic cooling, which greatly limited their use in everyday applications. [13]

In 2009 it was discovered that the act of unpeeling adhesive tape generates non-polarized terahertz radiation, with a narrow peak at 2 THz and a broader peak at 18 THz. The mechanism of its creation is tribocharging of the adhesive tape and subsequent discharge; this was hypothesized to involve bremsstrahlung with absorption or energy density focusing during dielectric breakdown of a gas. [14]

In 2013 researchers at Georgia Institute of Technology's Broadband Wireless Networking Laboratory and the Polytechnic University of Catalonia developed a method to create a graphene antenna: an antenna that would be shaped into graphene strips from 10 to 100 nanometers wide and one micrometer long. Such an antenna could be used to emit radio waves in the terahertz frequency range. [15] [16]

Research

Medical imaging

Unlike X-rays, terahertz radiation is not ionizing radiation and its low photon energies in general do not damage living tissues and DNA. 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 an imaging system that is safe, non-invasive, and painless.

The first images generated using terahertz radiation date from the 1960s; however, in 1995 images generated using terahertz time-domain spectroscopy generated a great deal of interest.

Some frequencies of terahertz radiation can be used for 3D imaging of teeth and may be more accurate 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 have unique spectral "fingerprints" in the terahertz range. This offers the possibility to combine spectral identification with imaging. In 2002 the European Space Agency (ESA) Star Tiger team, [17] based at the Rutherford Appleton Laboratory (Oxfordshire, UK), produced the first passive terahertz image of a hand. [18] By 2004, ThruVision Ltd, a spin-out from the Council for the Central Laboratory of the Research Councils (CCLRC) Rutherford Appleton Laboratory, had demonstrated the world’s first compact THz camera for security screening applications. The prototype system successfully imaged guns and explosives concealed under clothing. [19] Passive detection of terahertz signatures avoid the bodily privacy concerns of other detection by being targeted to a very specific range of materials and objects. [20] [21]

In January 2013, the NYPD announced plans to experiment with the new technology to detect concealed weapons, [22] prompting Miami blogger and privacy activist Jonathan Corbett to file a lawsuit against the department in Manhattan federal court that same month, challenging such use: "For thousands of years, humans have used clothing to protect their modesty and have quite reasonably held the expectation of privacy for anything inside of their clothing, since no human is able to see through them." He sought a court order to prohibit using the technology without reasonable suspicion or probable cause. [23] By early 2017, the department said it had no intention of ever using the sensors given to them by the federal government. [24]

Scientific use and imaging

In addition to its current use in submillimetre astronomy, terahertz radiation spectroscopy could provide new sources of information for chemistry and biochemistry.

Recently developed methods of THz time-domain spectroscopy (THz TDS) and THz tomography have been shown to be able to image samples that 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 spectrally broad, so such images can contain far more information than a conventional image formed with a single-frequency source.

Submillimeter waves are used in physics to study materials in high magnetic fields, since at high fields (over about 11  tesla), the electron spin Larmor frequencies are in the submillimeter band. Many high-magnetic field laboratories perform these high-frequency EPR experiments, such as the National High Magnetic Field Laboratory (NHMFL) in Florida.

Terahertz radiation could let art historians see murals hidden beneath coats of plaster or paint in centuries-old buildings, without harming the artwork. [25]

THz driven dielectric wakefield acceleration

New types of particle accelerators that could achieve multi Giga-electron volts per metre (GeV/m) accelerating gradients are of utmost importance to reduce the size and cost of future generations of high energy colliders as well as provide a widespread availability of compact accelerator technology to smaller laboratories around the world. Gradients in the order of 100 MeV/m have been achieved by conventional techniques and are limited by RF-induced plasma breakdown [26] . Beam driven dielectric wakefield accelerators (DWAs) [27] [28] typically operate in the Terahertz frequency range, which pushes the plasma breakdown threshold for surface electric fields into the multi-GV/m range [29] . DWA technique allows to accommodate a significant amount of charge per bunch, and gives an access to conventional fabrication techniques for the accelerating structures. To date 0.3 GeV/m accelerating and 1.3 GeV/m decelerating gradients [30] have been achieved using a dielectric lined waveguide with sub-millimetre transverse aperture.

An accelerating gradient larger than 1 GeV/m, can potentially be produced by the Cherenkov Smith-Purcell radiative mechanism [31] [32] in a dielectric capillary with a variable inner radius. When an electron bunch propagates through the capillary, its self-field interacts with the dielectric material and produces wakefields that propagate inside the material at the Cherenkov angle. The wakefields are slowed down below the speed of light, as the relative dielectric permittivity of the material is larger than 1. The radiation is then reflected from the capillary’s metallic boundary and diffracted back into the vacuum region, producing high accelerating fields on the capillary axis with a distinct frequency signature. In presence of a periodic boundary the Smith-Purcell radiation imposes frequency dispersion.

A preliminary study with corrugated capillaries has shown some modification to the spectral content and amplitude of the generated wakefields [33] , but the possibility of using Smith-Purcell effect in DWA is still under consideration.

Communication

In May 2012, a team of researchers from the Tokyo Institute of Technology [34] published in Electronics Letters that it had set a new record for wireless data transmission by using T-rays and proposed they be used as bandwidth for data transmission in the future. [35] The team's proof of concept device used a resonant tunneling diode (RTD) negative resistance oscillator to produce waves in the terahertz band. With this RTD, the researchers sent a signal at 542 GHz, resulting in a data transfer rate of 3 Gigabits per second. [35] [35] It doubled the record for data transmission rate set the previous November. [36] The study suggested that Wi-Fi using the system would be limited to approximately 10 metres (33 ft), but could allow data transmission at up to 100 Gbit/s. [35] [ clarification needed ] In 2011, Japanese electronic parts maker Rohm and a research team at Osaka University produced a chip capable of transmitting 1.5 Gbit/s using terahertz radiation. [37]

Potential uses exist in high-altitude telecommunications, above altitudes where water vapor causes signal absorption: aircraft to satellite, or satellite to satellite.[ citation needed ]


Manufacturing

Many possible uses of terahertz sensing and imaging are proposed in manufacturing, quality control, and process monitoring. These in general exploit the traits of plastics and cardboard being transparent to terahertz radiation, making it possible to inspect packaged goods. The first imaging system based on optoelectronic terahertz time-domain spectroscopy were developed in 1995 by researchers from AT&T Bell Laboratories and was used for producing a transmission image of a packaged electronic chip. [38] This system used pulsed laser beams with duration in range of picoseconds. Since then commonly used commercial/ research terahertz imaging systems have used pulsed lasers to generate terahertz images. The image can be developed based on either the attenuation or phase delay of the transmitted terahertz pulse. [39]

Since the beam is scattered more at the edges and also different materials have different absorption coefficients, the images based on attenuation indicates edges and different materials inside of an objects. This approach is similar to X-ray transmission imaging, where images are developed based on attenuation of the transmitted beam. [40]

In the second approach, terahertz images are developed based on the time delay of the received pulse. In this approach, thicker parts of the objects are well recognized as the thicker parts cause more time delay of the pulse. Energy of the laser spots are distributed by a Gaussian function. The geometry and behavior of Gaussian beam in the Fraunhofer region imply that the electromagnetic beams diverge more as the frequencies of the beams decrease and thus the resolution decreases. [41] This implies that terahertz imaging systems have higher resolution than scanning acoustic microscope (SAM) but lower resolution than X-ray imaging systems. Although terahertz can be used for inspection of packaged objects, it suffers from low resolution for fine inspections. X-ray image and terahertz images of an electronic chip are brought in the figure on the right. [42] Obviously the resolution of X-ray is higher than terahertz image, but X-ray is ionizing and can be impose harmful effects on certain objects such as semiconductors and live tissues.

To overcome low resolution of the terahertz systems near-field terahertz imaging systems are under development. [43] [44] In nearfield imaging the detector needs to be located very close to the surface of the plane and thus imaging of the thick packaged objects may not be feasible. In another attempt to increase the resolution, laser beams with frequencies higher than terahertz are used to excite the p-n junctions in semiconductor objects, the excited junctions generate terahertz radiation as a result as long as their contacts are unbroken and in this way damaged devices can be detected. [45] In this approach, since the absorption increases exponentially with the frequency, again inspection of the thick packaged semiconductors may not be doable. Consequently, a tradeoff between the achievable resolution and the thickness of the penetration of the beam in the packaging material should be considered.

Amateur radio

In the ITU Table of Frequency Allocations, no formal allocation to any radio service is present above 275 GHz, although the regulations themselves cover up to 3000 GHz (3 THz) and include footnote RR5.565 concerning this range. However, a number of administrations permit amateur radio experimentation within the 275–3000 GHz range on a national basis, under licence conditions that are usually based on RR5.565.

Safety

The terahertz region is between the radio frequency region and the optical region generally associated with lasers. Both the IEEE RF safety standard [46] and the ANSI Laser safety standard [47] have limits into the terahertz region, but both safety limits are based on extrapolation. It is expected that effects on tissues are thermal in nature and, therefore, predictable by conventional thermal models [ citation needed ]. Research is underway to collect data to populate this region of the spectrum and validate safety limits. [ citation needed ]

A study published in 2010 and conducted by Boian S. Alexandrov and colleagues at the Center for Nonlinear Studies at Los Alamos National Laboratory in New Mexico [48] created mathematical models predicting how terahertz radiation would interact with double-stranded DNA, showing that, even though involved forces seem to be tiny, nonlinear resonances (although much less likely to form than less-powerful common resonances) could allow terahertz waves to "unzip double-stranded DNA, creating bubbles in the double strand that could significantly interfere with processes such as gene expression and DNA replication". [49] Experimental verification of this simulation was not done. A recent analysis of this work concludes that the DNA bubbles do not occur under reasonable physical assumptions or if the effects of temperature are taken into account. [50] It should also be noted that the T-ray intensity drops to less than 1% in the first 500 μm of skin. [51]

See also

Related Research Articles

Maser Microwave Amplification by Stimulated Emission of Radiation

A maser is a device that produces coherent electromagnetic waves through amplification by stimulated emission. The first maser was built by Charles H. Townes, James P. Gordon, and H. J. Zeiger at Columbia University in 1953. Townes, Nikolay Basov and Alexander Prokhorov were awarded the 1964 Nobel Prize in Physics for theoretical work leading to the maser. Masers are used as the timekeeping device in atomic clocks, and as extremely low-noise microwave amplifiers in radio telescopes and deep space spacecraft communication ground stations.

Spectroscopy study of the interaction between matter and electromagnetic radiation

Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism. Later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency, predominantly in the electromagnetic spectrum, though matter waves and acoustic waves can also be considered forms of radiative energy; recently, with tremendous difficulty, even gravitational waves have been associated with a spectral signature in the context of LIGO and laser interferometry. Spectroscopic data are often represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency.

Indium phosphide chemical compound

Indium phosphide (InP) is a binary semiconductor composed of indium and phosphorus. It has a face-centered cubic ("zincblende") crystal structure, identical to that of GaAs and most of the III-V semiconductors.

Free-electron laser

A free-electron laser (FEL) is a kind of laser whose lasing medium consists of very-high-speed electrons moving freely through a magnetic structure, hence the term free electron. The free-electron laser is tunable and has the widest frequency range of any laser type, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, ultraviolet, and X-ray.

Terahertz time-domain spectroscopy

In physics, terahertz time-domain spectroscopy (THz-TDS) is a spectroscopic technique in which the properties of matter are probed with short pulses of terahertz radiation. The generation and detection scheme is sensitive to the sample's effect on both the amplitude and the phase of the terahertz radiation. By measuring in the time-domain, the technique can provide more information than conventional Fourier-transform spectroscopy, which is only sensitive to the amplitude. Since the time-domain, and consequently the frequency-domain, of the THz signal is available, the distorting effect of the diffraction can be mitigated and the resolution of the THz images can be enhanced substantially. This resolution enhancement process is illustrated in the Figure to the right.

Gunn diode diode

A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal passive semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1962 by physicist J. B. Gunn. Its largest use is in electronic oscillators to generate microwaves, in applications such as radar speed guns, microwave relay data link transmitters, and automatic door openers.

Far-infrared laser or terahertz laser is a laser with output wavelength in between 30-1000 µm, in the far infrared or terahertz frequency band of the electromagnetic spectrum.

Photomixing is the generation of continuous wave terahertz radiation from two lasers. The beams are mixed together and focused onto a photomixer device which generates the terahertz radiation. It is technologically significant because there are few sources capable of providing radiation in this waveband, others include frequency multiplied electronic/microwave sources, quantum cascade laser and ultrashort pulsed lasers with photoconductive switches as used in terahertz time-domain spectroscopy. The advantages of this technique are that it is continuously tunable over the frequency range from 300 GHz to 3 THz, and spectral resolutions in the order of 1 MHz can be achieved. However, the achievable power is on the order of 10−8 W.

Optical rectification non-linear optical process

Electro-optic rectification (EOR), also referred to as optical rectification, is a non-linear optical process that consists of the generation of a quasi-DC polarization in a non-linear medium at the passage of an intense optical beam. For typical intensities, optical rectification is a second-order phenomenon which is based on the inverse process of the electro-optic effect. It was reported for the first time in 1962, when radiation from a ruby laser was transmitted through potassium dihydrogen phosphate (KDP) and potassium dideuterium phosphate (KDdP) crystals.

Optical rectenna

An optical rectenna is a rectenna that works with visible or infrared light. A rectenna is a circuit containing an antenna and a diode, which turns electromagnetic waves into direct current electricity. While rectennas have long been used for radio waves or microwaves, an optical rectenna would operate the same way but with infrared or visible light, turning it into electricity.

Terahertz metamaterial

A terahertz metamaterial is a class of composite metamaterials designed to interact at terahertz (THz) frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz.

A metamaterial absorber is a type of metamaterial intended to efficiently absorb electromagnetic radiation such as light. Furthermore, metamaterials are an advance in materials science. Hence, those metamaterials that are designed to be absorbers offer benefits over conventional absorbers such as further miniaturization, wider adaptability, and increased effectiveness. Intended applications for the metamaterial absorber include emitters, photodetectors, sensors, spatial light modulators, infrared camouflage, wireless communication, and use in solar photovoltaics and thermophotovoltaics.

Terahertz nondestructive evaluation pertains to devices, and techniques of analysis occurring in the terahertz domain of electromagnetic radiation. These devices and techniques evaluate the properties of a material, component or system without causing damage.

Cosmology Large Angular Scale Surveyor array of microwave telescopes

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of microwave telescopes at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. The CLASS experiment aims to test the theory of cosmic inflation and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB) over 65% of the sky at multiple frequencies in the microwave region of the electromagnetic spectrum.

POlarization Emission of Millimeter Activity at the Sun

The POlarization Emission of Millimeter Activity at the Sun (POEMAS) is a solar patrol system composed of two radio telescopes with superheterodyne circular polarization receivers at 45 and 90 GHz. Since their half power beam width is around 1.4°, they observe the full sun. The acquisition system allows to gather 100 values per second at both frequencies and polarizations, with a sensitivity of around 20 solar flux units (SFU) (1 SFU ≡ 104 Jy). The telescope saw first light in November 2011, and showed excellent performance during two years, when it observed many flares. Since November 2013 is stopped for repairing. The main interest of POEMAS is the observation of solar flares in a frequency range where there are very few detectors and fill the gap between microwaves observed with the Radio Solar Telescope Network (1 to 15.4 GHz) and submillimeter observations of the Solar Submillimeter Telescope (212 and 405 GHz). Moreover, POEMAS is the only current telescope capable of carrying on circular polarization solar flare observations at 90 GHz. (Although, in principle, ALMA band 3 may also observe at 90 GHz with circular polarization).

References

  1. Jones, Graham A.; Layer, David H.; Osenkowsky, Thomas G. (2007). National Association of Broadcasters Engineering Handbook. Taylor and Francis. ISBN   978-1136034107.
  2. Ahi, Kiarash (26 May 2016). "Advanced terahertz techniques for quality control and counterfeit detection". Proc. SPIE 9856, Terahertz Physics, Devices, and Systems X: Advanced Applications in Industry and Defense, 98560G. Terahertz Physics, Devices, and Systems X: Advanced Applications in Industry and Defense. 9856: 98560G. Bibcode:2016SPIE.9856E..0GA. doi:10.1117/12.2228684 . Retrieved 26 May 2016.
  3. 1 2 Ahi, Kiarash (2018). "A Method and System for Enhancing the Resolution of Terahertz Imaging". Measurement. doi:10.1016/j.measurement.2018.06.044. ISSN   0263-2241.
  4. JLab generates high-power terahertz light. CERN Courier. 1 January 2003.
  5. Virginia Diodes Virginia Diodes Multipliers Archived 15 March 2014 at the Wayback Machine
  6. Köhler, Rüdeger; Alessandro Tredicucci; Fabio Beltram; Harvey E. Beere; Edmund H. Linfield; A. Giles Davies; David A. Ritchie; Rita C. Iotti; Fausto Rossi (2002). "Terahertz semiconductor-heterostructure laser". Nature. 417 (6885): 156–159. Bibcode:2002Natur.417..156K. doi:10.1038/417156a. PMID   12000955.
  7. Scalari, G.; C. Walther; M. Fischer; R. Terazzi; H. Beere; D. Ritchie; J. Faist (2009). "THz and sub-THz quantum cascade lasers". Laser & Photonics Review. 3 (1–2): 45–66. Bibcode:2009LPRv....3...45S. doi:10.1002/lpor.200810030.
  8. Lee, Alan W. M.; Qi Qin; Sushil Kumar; Benjamin S. Williams; Qing Hu; John L. Reno (2006). "Real-time terahertz imaging over a standoff distance (>25 meters)". Appl. Phys. Lett. 89 (14): 141125. Bibcode:2006ApPhL..89n1125L. doi:10.1063/1.2360210.
  9. Fathololoumi, S.; Dupont, E.; Chan, C. W. I.; Wasilewski, Z. R.; Laframboise, S. R.; Ban, D.; Matyas, A.; Jirauschek, C.; Hu, Q.; Liu, H. C. (13 February 2012). "Terahertz quantum cascade lasers operating up to ~200 K with optimized oscillator strength and improved injection tunneling". Optics Express. 20 (4): 3866–3876. Bibcode:2012OExpr..20.3866F. doi:10.1364/OE.20.003866. PMID   22418143 . Retrieved 21 March 2012.
  10. Ramakrishnan, Gopakumar (2012). Enhanced terahertz emission from thin film semiconductor/metal interfaces. Delft University of Technology, The Netherlands. ISBN   978-94-6191-5641.
  11. Brown, E. R.; SöDerström, J. R.; Parker, C. D.; Mahoney, L. J.; Molvar, K. M.; McGill, T. C. (1991). "Oscillations up to 712 GHz in InAs/AlSb resonant-tunneling diodes". Applied Physics Letters. 58 (20): 2291. Bibcode:1991ApPhL..58.2291B. doi:10.1063/1.104902.
  12. Science News: New T-ray Source Could Improve Airport Security, Cancer Detection, ScienceDaily (27 November 2007).
  13. Engineers demonstrate first room-temperature semiconductor source of coherent terahertz radiation Physorg.com. 19 May 2008. Retrieved May 2008
  14. Peeling adhesive tape emits electromagnetic radiation at terahertz frequencies www.opticsinfobase.org 6 August 2009. Retrieved August 2009
  15. Hewitt, John (25 February 2013). "Samsung funds graphene antenna project for wireless, ultra-fast intra-chip links". ExtremeTech . Retrieved 8 March 2013.
  16. Talbot, David (5 March 2013). "Graphene Antennas Would Enable Terabit Wireless Downloads". Technology Review . Massachusetts Institute of Technology . Retrieved 8 March 2013.
  17. "Space in Images – 2002 – 06 – Meeting the team". European Space Agency. June 2002.
  18. Space camera blazes new terahertz trails. timeshighereducation.co.uk. 14 February 2003.
  19. Winner of the 2003/04 Research Councils' Business Plan Competition – 24 February 2004. epsrc.ac.uk. 27 February 2004
  20. "Camera 'looks' through clothing". BBC News 24. 10 March 2008. Retrieved 10 March 2008.
  21. "ThruVision T5000 T-Ray Camera sees through Clothes". I4u.com. Retrieved 17 May 2012.
  22. Parascandola, Bruno (23 January 2013). "NYPD Commissioner says department will begin testing a new high-tech device that scans for concealed weapons". NYDailyNews.com. Retrieved 10 April 2013.
  23. Golding, Bruce & Conley, Kirsten (28 January 2013). "Blogger sues NYPD over gun detecting 'terahertz' scanners". NYpost.com. Retrieved 10 April 2013.
  24. Parascandola, Rocco (22 February 2017). "NYPD's pricey, controversial 'T-Ray' gun sensors sit idle, but that's OK with cops". New York Daily News. Retrieved 22 February 2017.
  25. Hidden Art Could be Revealed by New Terahertz Device Newswise, Retrieved 21 September 2008.
  26. Geometric dependence of radio-frequency breakdown in normal conducting accelerating structures Applied Physics Letters 97, 171501 (2010).
  27. Terahertz-driven linear electron acceleration Nature Communications DOI:10.1038/ncomms9486 (2015).
  28. Dielectric Wakefield Accelerators Review of Accelerator Science and Technology 9, 127 (2016).
  29. Breakdown limits on gigavolt-per-meter electron-beam-driven wakefields in dielectric structures Physical Review Letters 100, 214801 (2008).
  30. Observation of acceleration and deceleration in gigaelectron-volt-per-metre gradient dielectric wakefield accelerators Nature Communications DOI:10.1038/ncomms12763 (2016).
  31. Terahertz radiation from electrons moving through a waveguide with variable radius, based on Smith–Purcell and Cherenkov mechanisms Nuclear Instruments and Methods in Physics Research Section B 309, 223 (2013).
  32. Sub-THz radiation from dielectric capillaries with reflectors Nuclear Instruments and Methods in Physics Research Section B 402, 148 (2017).
  33. Driver-witness electron beam acceleration in dielectric mm-scale capillaries Phys. Rev. Accel. Beams 21, 051301 (2018).
  34. Ishigaki, K.; Shiraishi, M.; Suzuki, S.; Asada, M.; Nishiyama, N.; Arai, S. (2012). "Direct intensity modulation and wireless data transmission characteristics of terahertz-oscillating resonant tunnelling diodes". Electronics Letters. 48 (10): 582. doi:10.1049/el.2012.0849.
  35. 1 2 3 4 "Milestone for wi-fi with 'T-rays'". BBC News. 16 May 2012. Retrieved 16 May 2012.
  36. Chacksfield, Marc (16 May 2012). "Scientists show off the future of Wi-Fi – smash through 3Gbps barrier". Tech Radar. Retrieved 16 May 2012.
  37. New Chip Enables Record-Breaking Wireless Data Transmission Speed www.techcrunch.com 22 November 2011. Retrieved November 2011
  38. Hu, B. B.; Nuss, M. C. (15 August 1995). "Imaging with terahertz waves". Optics Letters. 20 (16): 1716. Bibcode:1995OptL...20.1716H. doi:10.1364/OL.20.001716.
  39. Chan, Wai Lam; Deibel, Jason; Mittleman, Daniel M (1 August 2007). "Imaging with terahertz radiation". Reports on Progress in Physics. 70 (8): 1325–1379. Bibcode:2007RPPh...70.1325C. doi:10.1088/0034-4885/70/8/R02.
  40. --, Jerry L. Prince, Jonathan M. Links. (2006). Medical imaging signals and systems. Upper Saddle River, N.J.: Pearson Prentice Hall. ISBN   978-0130653536.
  41. Marshall, edited by Gerald F.; Stutz, Glenn E. (2012). Handbook of optical and laser scanning (2nd ed.). Boca Raton, FL: CRC Press. ISBN   978-1439808795.CS1 maint: Extra text: authors list (link)
  42. Ahi, Kiarash (2015-05-13). "Terahertz characterization of electronic components and comparison of terahertz imaging with X-ray imaging techniques". SPIE Sensing Technology+ Applications. Terahertz Physics, Devices, and Systems IX: Advanced Applications in Industry and Defense. 9483: 94830K–94830K–15. Bibcode:2015SPIE.9483E..0KA. doi:10.1117/12.2183128.
  43. Mueckstein, Raimund; Mitrofanov, Oleg (3 February 2011). "Imaging of terahertz surface plasmon waves excited on a gold surface by a focused beam". Optics Express. 19 (4): 3212–7. Bibcode:2011OExpr..19.3212M. doi:10.1364/OE.19.003212. PMID   21369143.
  44. Adam, Aurele; Brok, Janne; Seo, Min Ah; Ahn, Kwang Jun; Kim, Dai Sik; Kang, Ji-Hun; Park, Q-Han; Nagel, M.; Nagel, Paul C. M. (19 May 2008). "Advanced terahertz electric near-field measurements at sub-wavelength diameter metallic apertures: erratum". Optics Express. 16 (11): 8054. Bibcode:2008OExpr..16.8054A. doi:10.1364/OE.16.008054.
  45. Kiwa, Toshihiko; Tonouchi, Masayoshi; Yamashita, Masatsugu; Kawase, Kodo (1 November 2003). "Laser terahertz-emission microscope for inspecting electrical faults in integrated circuits". Optics Letters. 28 (21): 2058. Bibcode:2003OptL...28.2058K. doi:10.1364/OL.28.002058.
  46. IEEE C95.1–2005, IEEE Standard for Safety Levels With Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz
  47. ANSI Z136.1–2007, American National Standard for Safe Use of Lasers
  48. Alexandrov, B. S. ; Gelev, V. ; Bishop, A. R. ; Usheva, A. ; Rasmussen, K. O. (2010). "DNA Breathing Dynamics in the Presence of a Terahertz Field". Physics Letters A . 374 (10): 1214–1217. arXiv: 0910.5294 . Bibcode:2010PhLA..374.1214A. doi:10.1016/j.physleta.2009.12.077. PMC   2822276 . PMID   20174451.CS1 maint: Multiple names: authors list (link)
  49. "How Terahertz Waves Tear Apart DNA". Technology Review . 30 October 2010. Retrieved 27 December 2010.
  50. Swanson, Eric S. (2010). "Modelling DNA Response to THz Radiation". Physical Review E. 83 (4): 040901. arXiv: 1012.4153 . Bibcode:2011PhRvE..83d0901S. doi:10.1103/PhysRevE.83.040901. PMID   21599106.
  51. A.J. Fitzgerald et al. Catalogue of Human Tissue Optical Properties at Terahertz Frequencies. Journal of Biological Physics 129: 123–128, 2003.