Applications of terahertz radiation: security

In the field of security THz technology has promising applications because of the ability of THz radiation to penetrate many materials, especially clothing and packaging materials. Also, many substances such as explosives have characteristic spectra in the THz range which might be used for identification. Research efforts are being devoted to the development of THz imaging and spectroscopy systems that are capable of detecting hidden threats, such as weapons or explosives, at stand-oft distances up to several tens of meters. In this lecture the principles of THz imaging and spectroscopy techniques for security applications will be presented. The physical processes on which the contrast of a THz image is based will be discussed. The strengths and weaknesses of passive and active imaging and a trade-off between both techniques will be analyzed. Examples of THz imaging systems and their main components such as detectors and radiation sources will be given. Also the potential of THz spectroscopy for identification of explosives will be discussed on the basis of recent results. The lecture will conclude with an outiook on the prospects of THz imaging and spectroscopy for security applications