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Proceedings Paper

Screening mail for powders using terahertz technology
Author(s): Mike Kemp
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Paper Abstract

Following the 2001 Anthrax letter attacks in the USA, there has been a continuing interest in techniques that can detect or identify so-called 'white powder' concealed in envelopes. Electromagnetic waves (wavelengths 100-500 μm) in the terahertz frequency range penetrate paper and have short enough wavelengths to provide good resolution images; some materials also have spectroscopic signatures in the terahertz region. We report on an experimental study into the use of terahertz imaging and spectroscopy for mail screening. Spectroscopic signatures of target powders were measured and, using a specially designed test rig, a number of imaging methods based on reflection, transmission and scattering were investigated. It was found that, contrary to some previous reports, bacterial spores do not appear to have any strong spectroscopic signatures which would enable them to be identified. Imaging techniques based on reflection imaging and scattering are ineffective in this application, due to the similarities in optical properties between powders of interest and paper. However, transmission imaging using time-of-flight of terahertz pulses was found to be a very simple and sensitive method of detecting small quantities (25 mg) of powder, even in quite thick envelopes. An initial feasibility study indicates that this method could be used as the basis of a practical mail screening system.

Paper Details

Date Published: 5 October 2011
PDF: 14 pages
Proc. SPIE 8189, Optics and Photonics for Counterterrorism and Crime Fighting VII; Optical Materials in Defence Systems Technology VIII; and Quantum-Physics-based Information Security, 81890J (5 October 2011); doi: 10.1117/12.898093
Show Author Affiliations
Mike Kemp, Iconal Technology Ltd. (United Kingdom)


Published in SPIE Proceedings Vol. 8189:
Optics and Photonics for Counterterrorism and Crime Fighting VII; Optical Materials in Defence Systems Technology VIII; and Quantum-Physics-based Information Security
Roberto Zamboni; Mark T. Gruneisen; Colin Lewis; Miloslav Dusek; Douglas Burgess; François Kajzar; Attila A. Szep; John G. Rarity, Editor(s)

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