Burnett, AD

Chowdhury, S

Davies, AG

Dean, P

Linfield, EH

Marshall, A

Valavanis, A

White Rose Research Online

This is a repository copy of Terahertz frequency imaging for explosives and weapons detection.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/88243/Version: Accepted VersionConference or Workshop Item:Valavanis, A, Dean, P, Burnett, AD et al. (4 more authors) Terahertz frequency imaging for explosives and weapons detection. In: Innovative Research Call in Explosives and Weapons Detection (2007) Showcase, 17 Nov 2011, London, United Kingdom. eprints@whiterose.ac.ukhttps://eprints.whiterose.ac.uk/Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version - refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher’s website. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Terahertz frequency imaging for explosives and weapons detectionA. Valavanis, P. Dean, A. D. Burnett, S. Chowdhury, A. Marshall, A. G. Davies andE. H. LinfieldSchool of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JTemail: a.valavanis@leeds.ac.ukThe terahertz (THz) region of the electromagnetic spectrum lies between microwave and infraredfrequencies, and has many potential benefits for security imaging. In particular, terahertz radiation canprovide spectral signatures of explosive compounds, illicit drugs and metallic objects, whilst passingthrough many common packaging and clothing materials with little attenuation. The relatively shortwavelength also allows high-resolution imaging of features smaller than 100µm. We have developedhigh power (> 50mW) and frequency-tunable sources operating in the 1–5THz spectral range, andused these in two demonstrations of terahertz imaging:Spectroscopic diffuse-reflectance imaging: We have shown that a common explosive (PETN)can be distinguished from a simple sugar (lactose monohydrate) at THz frequencies (Fig. 1(a)).[1] Weare also able to detect signatures of powdered solids at a 1.5m distance by measuring the back-scatteredradiation (Fig. 1(b)). This technique offers several advantages over the state of the art. Firstly, thickand/or highly-absorbing samples can be probed, unlike the case of transmission imaging. Secondly,there is no need for precise detector alignment, unlike specular-reflection imaging. Furthermore, wehave undertaken measurements through smooth containers, with no deterioration in signal.Self-mixing imaging: We have removed the need for any external radiation detector by couplingreflected radiation from an object back into the laser cavity.[2] This interference-sensing technique hasallowed us to demonstrate high-resolution imaging and sensing at distances in excess of 7m, and toobtain height-sensing of concealed objects (Fig. 1(c)).Our two demonstrations illustrate the potential of THz imaging technology as a potential ‘fieldable’compact system, and we are now seeking industrial partners to develop our research into demonstratorsystems for targeted applications.This project is funded under the Innovative Research Call in Explosives and Weapons Detec-tion (2007), a cross-government programme sponsored by a number of government departments andagencies under the CONTEST strategy.[1] P. Dean et al., Opt. Exp. 17, 20631 (2009)[2] P. Dean et al., Opt. Lett. 36, 2587 (2011)(a) (b) (c)Figure 1: (a) Difference-frequency images at 3.05 and 3.24THz illustrating contrast between PETNhigh-explosive and lactose monohydrate [left and right, respectively]. (b) Diffuse-reflectance image at2.8THz revealing a bag of powdered PTFE concealed within a visually-opaque envelope. (c) A 2.6THzself-mixing image of a concealed scalpel blade. Contours in the image reveal the surface-height.

Terahertz frequency imaging for explosives and weapons detection

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Terahertz frequency imaging for explosives and weapons detection

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