Terahertz (Tera Hertz, THz), also known as Terahertz, or Terahertz, is used to represent the frequency of electromagnetic waves, 1 Terahertz = 1 trillion Hertz. Terahertz is a new radiation source with many unique advantages. Terahertz waves generally refer to electromagnetic waves whose frequency is between infrared and microwave, and in the 0.1-10THz band.

Since terahertz waves are in the transition zone from macroelectronics to microphotonics, it is not completely suitable for treatment by optical theory, nor is it completely suitable for research by microwave theory.

For a long time in the past, the development of infrared and microwave technologies on both sides of the terahertz band has been relatively mature, but people’s understanding of the terahertz band is still very limited, forming the so-called “terahertz blank”.
In recent years, terahertz wave has attracted more and more attention from all over the world due to its unique performance and wide application prospects, and has been recognized by the international scientific community as a must-see in the high-tech field.
Its research and application will have great strategic significance for future operations and national security.
Terahertz technology is rated as one of the “Top Ten Technologies Changing the Future World” by the United States.

The reason why terahertz technology has attracted widespread attention in the scientific community is that the frequency of terahertz waves is higher than that of microwaves and lower than that of infrared rays; its energy is between electrons and photons. Compared with electromagnetic waves of other frequencies, it has many unique nature.

One is high penetration.

Terahertz waves have good penetrability to many dielectric materials and non-polar substances, and can perform perspective imaging on opaque objects, which is an effective complement to X-ray imaging and ultrasonic imaging technologies.

The second is low energy.

Terahertz photon energy is only about 1% of X-ray photon energy, and terahertz radiation will not cause photoionization and damage the quality of the test, which is very suitable for the inspection of human body or other biological samples. Water has a strong absorption of terahertz radiation, and terahertz waves are not easy to penetrate water-containing objects.

The third is transient.

The typical pulse width of terahertz pulses is on the order of picoseconds (ps, 10-12 seconds), and the interference of background radiation noise can be effectively suppressed through sampling measurement technology.

The fourth is coherence.

The coherence of terahertz is derived from its coherence mechanism, which can directly measure the amplitude and phase of the electric field, so as to facilitate the extraction of parameters such as the refractive index, absorption coefficient, extinction coefficient, and dielectric constant of the sample.

The unique properties of terahertz waves have great application prospects in communication, radar, electronic countermeasures, electromagnetic weapons, medical imaging, security inspection and other fields.

At present, the application of terahertz technology is still under continuous research and development, and its broad scientific prospects are recognized by the world.

One is the application of terahertz imaging.

Terahertz has a very high frequency and a very short wavelength. It has a high signal-to-noise ratio in the time-domain spectrum, and has very little transmission loss in dense smoke and dust environments. It can penetrate the wall to scan the interior of the house, which is a complex battlefield. Ideal technology for enemy-finding imaging in environments.
In future cities and anti-terrorism operations, with the help of terahertz’s unique “wall penetration”, three-dimensional imaging of objects “behind the wall” can be performed to detect hidden weapons, armed personnel in camouflage and ambushes, and display tanks in dust or smoke, Artillery and other equipment.

In addition, terahertz imaging technology is even more “clear” in the detection and identification of plastic murder weapons, ceramic pistols, plastic bombs, fluid explosives and human bombs.
Using strong terahertz radiation to irradiate the road surface can also detect the distribution of underground minefields at a long distance. Soldiers can inspect suspicious areas or people without getting close to them.
At present, this technology has been initially applied in security fields such as checking mail, identifying explosives and non-destructive flaw detection.

The second is the application of terahertz radar.

After the application of stealth technology, conventional narrow-band microwave radars often appear “powerless” when detecting stealth weapons with small radar cross-sections.
Terahertz, which is in the transitional region of the electromagnetic spectrum, is a combination of the advantages and disadvantages of many companies.

On the one hand, its wavelength is very short, about in the range of 30um-3mm, which can be used to detect smaller targets and more precise positioning.
On the other hand, it contains a wealth of frequencies, and can transmit nanosecond to picosecond pulses at thousands of frequencies, which greatly exceeds the scope of existing stealth technology.

Therefore, no matter when facing targets with invisible shapes, paint or plasma, it can make them “nowhere to hide”.
The United States was the first country to propose the concept of terahertz radar, and successively conducted high-resolution radar experiments such as 0.2THz, 1.56THz, and 0.6THz to verify the feasibility of terahertz radar.
As one of the development directions of high-precision and anti-stealth radar in the future, terahertz radar will have broad application prospects in the military.

The third is the application of terahertz communication.

The 500MHz-5GHz frequency band resources in the field of military communications have become increasingly scarce, and terahertz, a once “forgotten” band, integrates the advantages of microwave communication and optical communication, with high transmission rate, large capacity, strong directionality, and high security. And many other characteristics, such as good penetration, have become a hot spot for mining and development in various countries.

On the one hand, the frequency band of terahertz is 1-4 orders of magnitude higher than that of existing microwave communication, which means that it can carry a larger amount of information and meet the communication requirements of large data transmission rates on the battlefield.
On the other hand, the terahertz beam is narrower, with extremely high directionality, better confidentiality, strong anti-interference and penetration capabilities of clouds and camouflage, and can be used in harsh battlefields such as strong winds, sand and thick smoke. Directed, highly confidential, and even clear-text military communications with extremely high bandwidth in a wide range of environments.

Combining terahertz detectors with optical remote sensing technology can achieve spatial high resolution, fast imaging and spectral detection functions. Space terahertz passive remote sensing technology is currently the mainstream application direction of terahertz technology in the fields of astronomy and deep space exploration.

Many developed countries in Europe and the United States have implemented or are preparing to implement terahertz space programs, using space terahertz equipment to achieve scientific research on the composition of the earth’s atmosphere, the chemical properties of the troposphere and its dynamics to a certain extent.

Terahertz technology can be used to inspect spacecraft for damage, fatigue and chemical erosion. Terahertz imaging technology has now become one of the four major technologies used by NASA to detect spacecraft defects. For example, using terahertz technology to effectively detect, The cause of the tragedy on the “Columbia” was “external fuel tank foam debonding.”

Terahertz imaging technology can be applied to examine human tissue to find diseased areas, diagnose the degree of disease, and monitor the manufacture of medical drugs, etc. Terahertz time-domain spectroscopy technology can be used to test the quality of medicines and determine the ingredients of medicines.

Since the resonance frequency of vibration and rotation of biological macromolecules is in the terahertz band, terahertz also has good application prospects in agricultural and food processing industries such as grain selection and selection of excellent strains.

Terahertz time-domain spectroscopy technology can be used to measure the properties and internal structure of reservoir rocks, and to distinguish and identify rock types according to the measurement results.

The terahertz spectrometer has a high signal-to-noise ratio, and can perform non-destructive, non-ionizing, and highly sensitive spectral measurements of explosives. It is suitable for the identification and detection of hazardous chemicals. A large number of terahertz fingerprint databases for hazardous chemicals have been established at home and abroad.

The use of terahertz technology can be used for food testing, including water content testing, harmful component testing, banned chemical component testing, etc. Terahertz imaging can also be used to detect the quality of car dashboards, the integrity of the surface of walls and floor materials in buildings, the flatness of surfaces such as tiles and paper, and the delamination of printed circuit boards.

With the deepening understanding of the value of terahertz, countries have accelerated the exploration of this band, setting off a wave of research on terahertz.

At present, terahertz has received high attention, and many technologies have gradually matured.

Terahertz technology was listed as a key science of national defense in 2006, and many research institutions are actively developing this technology. The US Defense Advanced Research Projects Agency (DARPA) launched the TIFT project research to develop small-scale high-sensitivity terahertz sensing systems for security applications.

The Lawrence Berkeley National Laboratory of the United States has carried out research on advanced terahertz light sources and terahertz devices based on new semiconductor materials. The Stanford National Accelerator Laboratory in the United States has carried out research on ultra-short and high-peak power terahertz pulsed light sources based on accelerators and laser-plasma interactions.

Its Joint Propulsion Laboratory with Caltech has also made outstanding contributions to terahertz long-distance imaging and terahertz spectral imaging biomedical applications.

Focusing on the broad application prospects of terahertz technology, European governments and enterprises are increasingly active in the research and development of industry-university-research cooperation.

The UK carried out research on the WANTED project and developed a 1-10THz wide-area semiconductor vibrator and detector; carried out the TERAVISION project to develop a small medical terahertz pulse imaging device using high-power, small near-infrared short-pulse laser.

France has implemented the NANO-TERA project to study signal processing devices in the terahertz band.

The German Institute of High-Frequency Physics and Radar Technology has developed a terahertz imaging radar COBRA-220 with a working frequency of 0.22THz, with a working distance of 500 meters and an imaging resolution of 1.8 cm. Chalmers University of Technology in Sweden has manufactured a 0.34THz terahertz imaging radar based on frequency doubling link and heterodyne receiving link.

Danish researchers built a terahertz quasi-backward analog target scattering measurement system, the backscattering angle is about 6.6 degrees, and the system test frequency covers 0-3THz

Our country’s research on terahertz technology started relatively late, and research on terahertz human body security inspection technology and terahertz sensors has been carried out at present.

The terahertz human body security detector can realize rapid security inspection without contact, non-stop, and radiation during the security inspection process, and the detection efficiency is high.

The units involved in research and production mainly include Capital Normal University, Anhui Bowei Changan Electronics Co., Ltd., Beijing Aerospace Yilian Technology Development Co., Ltd., the 50th Research Institute of China Electronics Technology Group Corporation, the 38th Research Institute of China Electronics Technology Group Corporation, etc. , a number of scientific research institutions and enterprises. With the improvement of China’s scientific research and technology level in recent years, the gap between my country’s terahertz security detectors and foreign countries has been continuously narrowing.

Our country’s encouragement and support policies for terahertz sensors are continuously increasing. In the “14th Five-Year Plan” national key research and development plan “smart sensors” key project, it is proposed to explore new mechanisms and mechanisms for terahertz enhanced sensing to solve the problem of biochemical quantity detection of special substances. New methods to promote the application of terahertz technology in the field of medical testing.

Driven by the research programs of various countries, terahertz technology has made important breakthroughs, laying the foundation for its practical and commercialization. Terahertz technology has been recognized by the international scientific community as the foundation of the next-generation IT industry. While attracting the attention of scientists from all over the world, it has also attracted many large companies to enter the development of commercial products of terahertz technology. In recent years, the industrialization of terahertz technology has developed rapidly, including terahertz radiation source, terahertz detector, terahertz spectrum analysis system, terahertz imaging system and other industrialized technologies have been successfully applied in many fields.

At present, more than 80 high-tech companies in the world have developed and sold terahertz related products, and these companies are mainly concentrated in the United States and Europe. Well-known American companies, including IBM, VDI, Physical Science, etc., have turned their attention to the production of terahertz products. IBM has developed a silicon germanium terahertz microprocessor chip. The clock frequency of the chip can reach 0.35THz at room temperature, which is much higher than that of the standard PC processor chip. In a low temperature environment, the chip can achieve higher performance. The clock frequency can reach 0.5THz.

VDI mainly produces terahertz and millimeter wave solid-state oscillators and small integrated systems. The frequency of the products can reach up to 1.7THz. They are mainly used in satellite communications, astronomical exploration, meteorological monitoring, remote sensing imaging and other fields.

Picometrix, which was hatched by the University of Michigan and Stanford University in the United States, mainly produces terahertz inspection systems, which use terahertz imaging to inspect internal defects in the outer wall of spacecraft, and have been put into use. TeraView, a high-tech company incubated by the University of Cambridge in the UK, is engaged in the development of terahertz cameras. The TPI Imaga 1000 and TPIImaga 2000 three-dimensional imaging systems are the first commercial terahertz imaging systems in the world for physical and chemical properties of materials, which can be used for non-destructive analysis. and detection.

British company ThruVision specializes in the commercialization of terahertz imaging, has developed a passive terahertz imager, and currently has a commercial passive terahertz imaging system.

British company EI has produced terahertz gas lasers. In addition, a number of companies producing terahertz technology-related products have also emerged in Germany, Switzerland, France and other countries.