Terahertz technology in biological and chemical sensing for defence

The terahertz (1 THz = 1012 Hz, 3 mm or 33 cm(-1)) region of the electromagnetic spectrum is typically defined in the frequency range 100 GHz to 10 THz, corresponding to a wavelength range of 3 mm to 30 microns. Owing to a lack of suitable coherent sources and detectors, this region has only been investigated in earnest in the last ten years for terrestrial imaging and spectroscopy applications. Its role in the medical, pharmaceutical, non-destructive testing and more recently security industries is now being examined. The terahertz frequency range is of particular interest since it is able to probe several molecular interactions including the intermolecular vibrations, large amplitude vibrations and twisting and torsional modes. Molecules have also shown polarization sensitivity to the incident terahertz radiation. The ability of terahertz radiation to investigate conformational change makes it an important part of the electromagnetic spectrum. Terahertz radiation has the potential to provide additional information, which may complement other optically based sensing technologies. The use of terahertz technology in the security and defence industry is discussed, with a specific focus on biological and chemical sensing. The challenges faced in bringing terahertz technology into the market place will be discussed.