The Terahertz Gap

The electromagnetic spectrum contains a variety of phenomena that we are all very familiar with, including visible light, x-rays and radio waves.  These different “types” of electromagnetic radiation are defined by their wavelength. The wavelength, frequency and energy of electromagnetic radiation are all directly connected and it is also common to come across electromagnetic radiation being defined by frequency.  White light from a lamp or the sun contains a range of wavelengths (or frequencies) that can be seen when the light is bent and a rainbow is produced. 

Although electromagnetic radiation from across the electromagnetic spectrum exists in nature (for example, gamma ray bursts are produced from supernovae, neutron stars and black holes and radio waves are produced by lightening), for us to harness parts of the spectrum for our own use requires both that we can produce (or emit) the appropriate part of the spectrum as and when needed and that we can then detect (and measure) the resulting radiation. 

Humans have already been very successful in generating and applying electromagnetic radiation –  x-ray imaging in medicine, communication via radiowaves, and quick cooking using microwaves.  However there remains a wide under-utilised gap in the “terahertz”  (THz) region. The prefix "tera" represents 1,000,000,000,000 or 1012This is the region where the electromagnetic radiation has a frequency of between approximately 0.1 - 10 THz.   The wavelength of terahertz radiation ranges from approximately 0.03 mm - 3mm, which explains why this part of the spectrum is also know as "sub-millimetre".



Image: Byrd et al https://commons.wikimedia.org/wiki/File:Thz_freq_in_EM_spectrum.png?uselang=en-gb

Although terahertz radiation is common in nature (almost half of the cosmic radiation background is at terahertz frequencies), terahertz waves have proved difficult to produce artificially and difficult to detect.  Fortunately, given the many potential applications, science and technology has improved and there is now a concerted research effort to harness the terahertz part of the spectrum.


Why are terahertz frequencies so useful?


Why have terahertz frequencies been difficult to produce and detect?


Applications


Further Reading