The terahertz gap is an engineering term for a band of frequencies 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 (wavelengths of 3 mm to 30 µm). Currently, at frequencies within this range, useful power generation and receiver technologies are inefficient and impractical. Mass production of devices in this range and operation at room temperature (at which kT is equal to the energy of a photon with a frequency of 6.2 THz) are mostly unfeasible. Hence, a gap exists between mature microwave technologies in the highest frequencies of the radio spectrum and the well developed optical engineering of infrared detectors in their lowest frequencies. Research that attempts to resolve this issue has been conducted since the late 20th century.
Ongoing investigation has resulted in improved emitters (sources) and detectors, and research in this area has intensified. However, drawbacks remain that include the substantial size of emitters, incompatible frequency ranges, and undesirable operating temperatures, as well as component, device, and detector requirements that are somewhere between solid state electronics and photonic technologies.
Free-electron lasers can generate a wide range of stimulated emission of electromagnetic radiation from microwaves, through terahertz radiation to X-ray. However, they are bulky, expensive and not suitable for applications that require critical timing (such as wireless communications).
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...researchers have successfully generated intense pulses of light in a largely untapped part of the electromagnetic spectrum – the so-called terahertz gap.