Terahertz remote sensing

The subject of this article is implementation of terahertz remote sensing for detection and imaging of concealed objects from distances of several metres. Many materials used for packaging and clothing are partially transparent in the spectral range 0.1 - 10 THz. The transparency property can be utilised to detect objects concealed by the materials, which are often opaque in other spectral regions. This can be achieved by detecting the radiation from these objects through the use of an appropriate detector, which is sensitive at THz frequencies. The radiation from the concealed objects can be either self-emitted or reflected. The use of THz remote sensing is being pursued in IARD by both theoretical and practical approaches. The article contains a short review on the detectors, sources and components, which can be used for remote sensing systems operating at THz frequencies, and describes energy calculations and system design considerations. Characteristic and exemplar performance of the components, which are being used in IARD, is presented. The article then describes prototypes of a passive THz radiometer and an active THz system, which were built in IARD. Performance characteristics of both systems are described. The measurement results of the optical properties of various materials are presented as well as examples of images obtained by the active THz system.