Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (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), although the upper boundary is somewhat arbitrary and is considered by some sources as 30 THz. One terahertz is 1012 Hz or 1000 GHz. Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.01 mm = 10 µm. Because terahertz radiation begins at a wavelength of around 1 millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared, and can be regarded as either.
|0.3 THz to 3 THz|
|1 mm to 100 μm|
|EU / NATO / US ECM|
|Other TV and radio|
Terahertz radiation is strongly absorbed by the gases of the atmosphere, and in air is attenuated to zero within a few meters, so it is not practical for terrestrial radio communication. It 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 a lower-energy alternative to X-rays for producing high resolution images of the interior of solid objects.
Terahertz radiation occupies a middle ground where the ranges of microwaves and infrared light waves overlap, known as the “terahertz gap”; it is called a “gap” because the technology for its generation and manipulation is still in its infancy. The generation and modulation of electromagnetic waves 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.
Terahertz radiation falls in between infrared radiation and microwave radiation in the electromagnetic spectrum, and it shares some properties with each of these. Terahertz radiation travels in a line of sight and is non-ionizing. Like microwaves, terahertz radiation can penetrate a wide variety of non-conducting materials; clothing, paper, cardboard, wood, masonry, plastic and ceramics. The penetration depth is typically less than that of microwave radiation. Like infrared, terahertz radiation has limited penetration through fog and clouds and cannot penetrate liquid water or metal. Terahertz radiation can penetrate some distance through body tissue like x-rays, but unlike them is non-ionizing, 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).
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 0.3–1.0 THz range (the lower part of the spectrum), including gyrotrons, backward wave oscillators, and resonant-tunneling diodes.
Terahertz versus submillimeter waves
The terahertz band, covering the wavelength range between 0.1–1 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.
Terahertz radiation is emitted as part of the black-body radiation from anything with a temperature greater than about 2 kelvins. While this thermal emission is very weak, observations at these frequencies are important for characterizing cold 10–20 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. Due to Earth's atmospheric absorption spectrum, the opacity of the atmosphere to submillimeter radiation restricts these observatories to very high altitude sites, or to space.
As of 2012, viable sources of terahertz radiation are the gyrotron, the backward wave oscillator ("BWO"), the organic gas far infrared laser, Schottky diode multipliers, varactor (varicap) multipliers, quantum cascade laser, the free electron laser, 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, and electronic oscillators based on resonant tunneling diodes have been shown to operate up to 700 GHz.
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. 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.
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.
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.
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. In response to the demand for COVID-19 screening terahertz spectroscopy and imaging has been proposed as a rapid screening tool.
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.
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, based at the Rutherford Appleton Laboratory (Oxfordshire, UK), produced the first passive terahertz image of a hand. 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. 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.
In January 2013, the NYPD announced plans to experiment with the new technology to detect concealed weapons, 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. By early 2017, the department said it had no intention of ever using the sensors given to them by the federal government.
Scientific use and imaging
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.
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. Beam driven dielectric wakefield accelerators (DWAs) typically operate in the Terahertz frequency range, which pushes the plasma breakdown threshold for surface electric fields into the multi-GV/m range. 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 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 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, but the possibility of using Smith-Purcell effect in DWA is still under consideration.
In May 2012, a team of researchers from the Tokyo Institute of Technology 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. 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. It doubled the record for data transmission rate set the previous November. 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. 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.
Potential uses exist in high-altitude telecommunications, above altitudes where water vapor causes signal absorption: aircraft to satellite, or satellite to satellite.
A number of administrations permit amateur radio experimentation within the 275–3000 GHz range or at even higher frequencies on a national basis, under license conditions that are usually based on RR5.565 of the ITU Radio Regulations. Amateur radio operators utilizing submillimeter frequencies often attempt to set two-way communication distance records, In the U.S.A. WA1ZMS and W4WWQ set a record of 1.42 kilometres (0.88 mi) on 403 GHz using CW (Morse code) on 21 December 2004. In Australia, at 30 THz a distance of 60 metres (200 ft) was achieved by stations VK3CV and VK3LN on 8 November 2020.
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. 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.
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.
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. 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. 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. 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. 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.
The terahertz region is between the radio frequency region and the laser optical region. Both the IEEE RF safety standard and the ANSI Laser safety standard 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 . Research is underway to collect data to populate this region of the spectrum and validate safety limits.
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 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". 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. The T-ray intensity drops to less than 1% in the first 500 μm of skin.
- Far-infrared laser
- Full body scanner
- Heterojunction bipolar transistor
- High-electron-mobility transistor (HEMT)
- Terahertz time-domain spectroscopy
- Jones, Graham A.; Layer, David H.; Osenkowsky, Thomas G. (2007). National Association of Broadcasters Engineering Handbook. Taylor and Francis. p. 7. ISBN 978-1-136-03410-7.
- "Article 2.1: Frequency and wavelength bands". Radio Regulations (zipped PDF) (2016 ed.). International Telecommunications Union. 2017. Retrieved 9 November 2019.
- Dhillon, S.S.; Vitiello, M.S.; Linfield, E.H.; Davies, A.G.; Hoffmann, Matthias C.; Booske, John; et al. (2017). "The 2017 terahertz science and technology roadmap". Journal of Physics D: Applied Physics. 50 (4): 2. doi:10.1088/1361-6463/50/4/043001.
- Coutaz, Jean-Louis; Garet, Frederic; Wallace, Vincent P. (2018). Principles of Terahertz Time-Domain Spectroscopy: An introductory textbook. CRC Press. p. 18. ISBN 9781351356367 – via Google Books.
- Siegel, Peter (2002). "Studying the Energy of the Universe". NASA. Education materials. U.S. National Aeronautics and Space Administration. Retrieved 19 May 2021.
- Ahi, Kiarash; Anwar, Mehdi F. (26 May 2016). "Advanced terahertz techniques for quality control and counterfeit detection". In Anwar, Mehdi F.; Crowe, Thomas W.; Manzur, Tariq (eds.). Proceedings SPIE Volume 9856, Terahertz Physics, Devices, and Systems X: Advanced Applications in Industry and Defense. SPIE Commercial + Scientific Sensing and Imaging. Baltimore, MD: SPIE: The International Society for Optics and Photonics. Bibcode:2016SPIE.9856E..0GA. doi:10.1117/12.2228684. S2CID 138587594. 98560G. Retrieved 26 May 2016 – via researchgate.net.
- Ahi, Kiarash (2018). "A method and system for enhancing the resolution of terahertz imaging". Measurement. 138: 614–619. doi:10.1016/j.measurement.2018.06.044. ISSN 0263-2241.
- "JLab generates high-power terahertz light". CERN Courier. 1 January 2003.
- "Atmospheric Absorption & Transmission". Humboldt State Geospatial Online Learning Modules. Humboldt State University. Archived from the original on 7 November 2020. Retrieved 19 May 2021.
- "Absorption Bands and Atmospheric Windows". The Earth Observatory. NASA. Retrieved 19 May 2021.
- "Multipliers". Products. Virginia Diodes. Archived from the original on 15 March 2014.
- Köhler, Rüdeger; Tredicucci, Alessandro; Beltram, Fabio; Beere, Harvey E.; Linfield, Edmund H.; Davies, A. Giles; Ritchie, David A.; Iotti, Rita C.; Rossi, Fausto (2002). "Terahertz semiconductor-heterostructure laser". Nature. 417 (6885): 156–159. Bibcode:2002Natur.417..156K. doi:10.1038/417156a. PMID 12000955. S2CID 4422664.
- Scalari, G.; Walther, C.; Fischer, M.; Terazzi, R.; Beere, H.; Ritchie, D.; Faist, J. (2009). "THz and sub-THz quantum cascade lasers". Laser & Photonics Reviews. 3 (1–2): 45–66. Bibcode:2009LPRv....3...45S. doi:10.1002/lpor.200810030.
- Lee, Alan W.M.; Qin, Qi; Kumar, Sushil; Williams, Benjamin S.; Hu, Qing; Reno, John L. (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. S2CID 122942520.
- Fathololoumi, S.; Dupont, E.; Chan, C.W.I.; Wasilewski, Z.R.; Laframboise, S.R.; Ban, D.; et al. (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. hdl:1721.1/86343. PMID 22418143.
- Ramakrishnan, Gopakumar (2012). Enhanced terahertz emission from thin film semiconductor/metal interfaces. Delft University of Technology, The Netherlands. ISBN 978-94-6191-5641.
- 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. S2CID 53364355.
- Science News: New T-ray Source Could Improve Airport Security, Cancer Detection, ScienceDaily (27 November 2007).
- Engineers demonstrate first room-temperature semiconductor source of coherent terahertz radiation Physorg.com. 19 May 2008. Retrieved May 2008
- Horvat, J.; Lewis, R. A. (2009). "Peeling adhesive tape emits electromagnetic radiation at terahertz frequencies". Optics Letters. 34 (14): 2195–7. Bibcode:2009OptL...34.2195H. doi:10.1364/OL.34.002195. PMID 19823546.
- Hewitt, John (25 February 2013). "Samsung funds graphene antenna project for wireless, ultra-fast intra-chip links". ExtremeTech. Retrieved 8 March 2013.
- Talbot, David (5 March 2013). "Graphene Antennas Would Enable Terabit Wireless Downloads". Technology Review. Massachusetts Institute of Technology. Retrieved 8 March 2013.
- Sun, Q.; He, Y.; Liu, K.; Fan, S.; Parrott, E. P. J.; Pickwell-MacPherson, E. (2017). "Recent advances in terahertz technology for biomedical applications". Quant Imaging Med Surg. AME Publishing Company. 7 (3): 345–355. doi:10.21037/qims.2017.06.02. ISSN 2223-4306. PMC 5537133. PMID 28812001.
- "Terahertz spectroscopy opens options in COVID-19 screening". LabPulse.com. Retrieved 14 June 2021.
- , "Method and System for Enhancing Resolution of Terahertz Imaging and Detection of Symptoms of COVID-19", issued 2020-10-21
- "Space in Images – 2002 – 06 – Meeting the team". European Space Agency. June 2002.
- Space camera blazes new terahertz trails. timeshighereducation.co.uk. 14 February 2003.
- Winner of the 2003/04 Research Councils' Business Plan Competition – 24 February 2004. epsrc.ac.uk. 27 February 2004
- "Camera 'looks' through clothing". BBC News 24. 10 March 2008. Retrieved 10 March 2008.
- "ThruVision T5000 T-Ray Camera sees through Clothes". I4u.com. Retrieved 17 May 2012.
- 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.
- Golding, Bruce & Conley, Kirsten (28 January 2013). "Blogger sues NYPD over gun detecting 'terahertz' scanners". NYpost.com. Retrieved 10 April 2013.
- 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.
- Hidden Art Could be Revealed by New Terahertz Device Newswise, Retrieved 21 September 2008.
- Dolgashev, Valery; Tantawi, Sami; Higashi, Yasuo; Spataro, Bruno (25 October 2010). "Geometric dependence of radio-frequency breakdown in normal conducting accelerating structures". Applied Physics Letters. 97 (17): 171501. doi:10.1063/1.3505339. ISSN 0003-6951.
- Nanni, Emilio A.; Huang, Wenqian R.; Hong, Kyung-Han; Ravi, Koustuban; Fallahi, Arya; Moriena, Gustavo; Dwayne Miller, R. J.; Kärtner, Franz X. (6 October 2015). "Terahertz-driven linear electron acceleration". Nature Communications. 6 (1): 8486. doi:10.1038/ncomms9486. ISSN 2041-1723. PMC 4600735. PMID 26439410.
- Jing, Chunguang (2016). "Dielectric Wakefield Accelerators". Reviews of Accelerator Science and Technology. 09: 127–149. doi:10.1142/s1793626816300061. ISSN 1793-6268.
- Thompson, M.C.; Badakov, H.; Cook, A.M.; Rosenzweig, J.B.; Tikhoplav, R.; Travish, G.; et al. (27 May 2008). "Breakdown limits on gigavolt-per-meter electron-beam-driven wakefields in dielectric structures". Physical Review Letters. 100 (21): 214801. doi:10.1103/physrevlett.100.214801. ISSN 0031-9007. OSTI 933022. PMID 18518609.
- O’Shea, B.D.; Andonian, G.; Barber, S.K.; Fitzmorris, K.L.; Hakimi, S.; Harrison, J.; et al. (14 September 2016). "Observation of acceleration and deceleration in gigaelectron-volt-per-metre gradient dielectric wakefield accelerators". Nature Communications. 7 (1): 12763. doi:10.1038/ncomms12763. ISSN 2041-1723. PMC 5027279. PMID 27624348.
- Ponomarenko, A.A.; Ryazanov, M.I.; Strikhanov, M.N.; Tishchenko, A.A. (2013). "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: Beam Interactions with Materials and Atoms. 309: 223–225. doi:10.1016/j.nimb.2013.01.074. ISSN 0168-583X.
- Lekomtsev, K.; Aryshev, A.; Tishchenko, A.A.; Shevelev, M.; Ponomarenko, A.A.; Karataev, P.; et al. (2017). "Sub-THz radiation from dielectric capillaries with reflectors". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. 402: 148–152. arXiv:1706.03054. doi:10.1016/j.nimb.2017.02.058. ISSN 0168-583X. S2CID 119444425.
- Lekomtsev, K.; Aryshev, A.; Tishchenko, A.A.; Shevelev, M.; Lyapin, A.; Boogert, S.; et al. (10 May 2018). "Driver-witness electron beam acceleration in dielectric mm-scale capillaries". Physical Review Accelerators and Beams. 21 (5): 051301. doi:10.1103/physrevaccelbeams.21.051301. ISSN 2469-9888.
- 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.
- "Milestone for Wi-Fi with 'T-rays'". BBC News. 16 May 2012. Retrieved 16 May 2012.
- Chacksfield, Marc (16 May 2012). "Scientists show off the future of Wi-Fi – smash through 3Gbps barrier". Tech Radar. Retrieved 16 May 2012.
- "New chip enables record-breaking wireless data transmission speed". techcrunch.com. 22 November 2011. Retrieved 30 November 2011.
- Clausell, A. (11 September 2020). Distance records (PDF). ARRL.org (Report). World above 50 MHz standings. American Radio Relay League. Retrieved 19 November 2020.
- Day, Peter; Qaurmby, John (9 May 2019). Microwave distance records (Report). UK Microwave Group. Retrieved 2 August 2019.
- Australian VHF-UHF records (PDF) (Report). Wireless Institute of Australia. 5 January 2021. Retrieved 5 January 2021.
- 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. PMID 19862134. S2CID 11593500.
- 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. S2CID 17397271.
- Prince, Jerry L., Jr.; Links, Jonathan M. (2006). Medical imaging signals and systems. Upper Saddle River, N.J.: Pearson Prentice Hall. ISBN 978-0130653536.
- Marshall, Gerald F.; Stutz, Glenn E., eds. (2012). Handbook of optical and laser scanning (2nd ed.). Boca Raton, FL: CRC Press. ISBN 978-1439808795.
Ahi, Kiarash; Shahbazmohamadi, Sina; Tehranipoor, Mark; Anwar, Mehdi (13 May 2015). https://www.researchgate.net/publication/278034592
|url=missing title (help). In Anwar, Mehdi F.; Crowe, Thomas W.; Manzur, Tariq (eds.). Proceedings Volume 9483, Terahertz Physics, Devices, and Systems IX: Advanced Applications in Industry and Defense. SPIE Sensing Technology + Applications. Baltimore, MD. Bibcode:2015SPIE.9483E..0KA. doi:10.1117/12.2183128. S2CID 118178651. 94830K – via researchgate.net.
- 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): 3212–3217. Bibcode:2011OExpr..19.3212M. doi:10.1364/OE.19.003212. PMID 21369143. S2CID 21438398.
- 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.
- 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): 2058–60. Bibcode:2003OptL...28.2058K. doi:10.1364/OL.28.002058. PMID 14587814.
- IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz (Report). Institute of Electrical and Electronics Engineers. 2005. IEEE C95.1–2005.
- American National Standard for Safe Use of Lasers (Report). American National Standards Institute. 2007. ANSI Z136.1–2007.
- 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.
"How terahertz waves tear apart DNA". MIT Technology Review. Emerging Technology from the arXiv. 30 October 2010. Retrieved 5 June 2021;
MIT Tech. Rev. article cites Alexandrov et al. (2010) as source.
- 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. S2CID 23117276.
- Fitzgerald, A.J.; Berry, E.; Zinov'Ev, N.N.; Homer-Vanniasinkam, S.; Miles, R.E.; Chamberlain, J.M.; Smith, M.A. (2003). "Catalogue of human tissue optical properties at terahertz frequencies". Journal of Biological Physics. 29 (2–3): 123–128. doi:10.1023/A:1024428406218. PMC 3456431. PMID 23345827.