SOME PHYSICAL ASPECTS OF THE TERAHERZ RANGE APPLICATIONS

Today, terahertz is broadly applied to submillimeter-wave energy that fills the wavelength range between 1- 0.1 mm (300 GHz-3 THz). Below 300 GHz, we cross into the millimeter-wave bands. Beyond 3 THz, and out to 0.03 mm (10 THz) is more or less unclaimed territory, as few if any components exist. Despite great scientific interest since at least the 1920s, the terahertz frequency range remain one of the least tapped regions of the electromagnetic spectrum. Sandwiched between traditional microwave and optical technologies where there is a limited atmospheric propagation path, little commercial emphasis has been placed on terahertz systems. Recently, the teraherz range is in the fast progress and many efforts are making for research and development of sensitive and fast detectors, rather powerful and tunable sources, waveguide and cavities components as well as the effective fields of teraherz application.

The following items of the subject will be presented in the report.

A. Possibilities of sensitive detecting at room and low temperatures.
The wavelength range from 1 mm to 0.1 mm corresponds to an approximate photon energy between 1.2-12.4 meV or to an equivalent black body temperature between 14-140 K, well below the ambient background on Earth. Physical limits as well as requirements to receiving teraherz systems will be estimated basing on black body radiation spectrum and energy distribution.

B. Waveguide lines and cavities in the teraherz range.
The principles of quasi-optics will be shortly discussed and main features of the quasi-optical waveguide lines and cavities will be presented.

C. Materials in the teraherz range.
The main parameters of dielectrics and metals which are usually used in teraherz components and devices will be discussed. A distinct change of metal parameters presents when the frequency increases from the microwave to the teraherz range.

D. Sources of coherent radiation in the teraherz range.
The outlook for the microwave-type tube (backward-wave tubes or carcinotrons, gyrotrons, orotrons, et cetera) as teraherz radiation sources is discussed. Submillimeter free-electron lasers of rather big power and tunability are also presented.

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