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Terahertz radiation has a frequency of about one trillion cycles per second and is found between long wavelength infrared radiation and short wavelength microwave radiation. It is emitted by all objects but is difficult to generate and observe. Terahertz waves can travel through non-conductive materials and have applications in medical imaging, security, materials analysis, and more.
Terahertz means one trillion cycles per second. Most often, the phrase is applied to a type of radiation that has a frequency of about a trillion cycles per second. The term could also apply to anything that happens a trillion times per second, such as certain atomic vibrations or futuristic computers with clock speeds several hundred times faster than today’s. In technology and industry, terahertz waves are of great interest because this portion of the spectrum is one of the hardest to generate and is just starting to be exploited. Terahertz radiation is sometimes considered a subset of infrared radiation.
The terahertz part of the electromagnetic spectrum is defined as radiation with a frequency between 300 gigahertz (3×1011 Hz) and 3 terahertz (3×1012 Hz), corresponding to wavelengths between 1 millimeter and 100 micrometres. This puts these waves between long wavelength infrared radiation and short wavelength microwave radiation. Because of their submillimeter wavelength, these waves are also called submillimeter waves, as reflected in astronomical facilities that capture these waves from the cosmos, such as the Caltech Submillimeter Observatory in California and the Heinrich Hertz Submillimeter Telescope in Arizona.
Like infrared waves, of which terahertz waves are sometimes considered a part, terahertz radiation is emitted in small amounts by all objects at any temperature, which means everything in the universe. However, unlike waves in the near infrared spectrum, terahertz waves are found in small numbers. Like infrared and microwaves, they travel in straight lines and are non-ionizing, safe, and non-radioactive. They can travel through a variety of non-conductive materials, including clothing, paper, cardboard, wood, buildings, ceramics, and plastics. They can also travel through fog and clouds, more effectively than infrared, but not through metal or water. Like infrared light, these waves are almost completely blocked by the Earth’s atmosphere.
Terahertz waves have proven difficult to generate and observe, as reliable sources of terahertz radiation only developed in the 1990s. These include the gyrotron, backward wave oscillator, synchrotron light sources, far infrared laser, quantum cascade laser, free electron laser, and photomixing sources. Since the 1990s, research into these waves has taken off, through to commercialization and application of this radiation has been slow. Applications that have been launched include medical imaging, security, materials analysis, studying condensed matter in strong magnetic fields, submillimeter astronomy, viewing old layers of paint on a work of art , satellite-to-satellite or aircraft-to-satellite communication, and quality control imaging for manufacturing.
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