Alhathlool, R

Burnett, AD

Chowdhury, S

Davies, AG

Dean, P

Indjin, D

Khanna, SP

Kliese, R

Lachab, M

Lim, YL

Linfield, EH

Nikolic, M

Rakic, AD

Valavanis, A

Wilson, S

English

White Rose Research Online

promoting access to White Rose research papersWhite Rose Research Onlineeprints@whiterose.ac.ukUniversities of Leeds, Sheffield and Yorkhttp://eprints.whiterose.ac.uk/This is the author’s version of a Proceedings Paper presented at the UKSemiconductors conference 2012, Sheffield, UKValavanis, A, Dean, P, Lim, YL, Alhathlool, R, Burnett, AD, Chowdhury, S, Kliese,R, Nikolic, M, Khanna, SP, Lachab, M, Indjin, D, Wilson, S, Rakic, AD, Davies,AG and Linfield, EH Detection of concealed weapons and characterisation ofcrystalline powders using terahertz quantum cascade lasers. In: UNSPECIFIEDUK Semiconductors 2012, Sheffield, UK.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/id/eprint/75404Detection of concealed weapons and characterisation of crystalline powders using terahertz quantum cascade lasers  A. Valavanis1,*, P. Dean1, Y. L. Lim2, R. Alhathlool1, A. D. Burnett1, S. Chowdhury1, R. Kliese2, M. Nikolić2, S. P. Khanna1, M. Lachab1, D. Indjin1, S. J. Wilson2, A. D. Rakić2, A. G. Davies1, and E. H. Linfield1  1School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK 2School of IT and Electrical Engineering, The University of Queensland, QLD 4072, Australia  *a.valavanis@leeds.ac.uk  Terahertz (THz)-frequency radiation (located between the microwave and infrared parts of the electromagnetic spectrum) offers many potential benefits for security sensing. In particular, it propagates through many common packaging materials, and excites material-specific resonances in crystalline compounds.1 However, THz sources are typically too large, expensive or low-powered for many applications. We present two imaging techniques that exploit THz quantum cascade lasers (QCLs)—compact semiconductor sources of intense coherent 1–5 THz radiation. Self-mixing-interferometry imaging of concealed objects: When THz radiation is partially reflected from objects back into a QCL, intra-cavity interference (self-mixing) causes measurable changes in terminal voltage, depending on the amplitude and phase of the reflections.2 This removes the need for an external detector and allows imaging of metallic objects (Fig. 1a) at up to 21 m round-trip distances. The 3D surface-profile may then be inferred from the phase of the interference. Spectroscopic diffuse-reflectance imaging: We measure backscattered radiation from powders illuminated by a tuneable 3–3.4 THz QCL. Unlike transmittance imaging, this technique does not require precise detector alignment, and arbitrarily-thick samples may be scanned.3 Diffuse reflectance measurements reproduce THz spectral features accurately and we show that material-specific resonances may be obtained for a range of materials (Fig. 1b). This work was funded by the ERC Advanced Grants 'TOSCA', EPSRC (UK), the Innovative Research Call in Explosives and Weapons Detection (2007), a cross-government programme sponsored by a number of government departments and agencies under the CONTEST strategy, and the Australian Research Council’s Discovery Projects funding scheme (DP120103703). 1. M. Tonouchi, Nat. Photonics 1, 97 (2007). 2. P. Dean, et al., Opt. Lett. 36, 2587 (2011). 3. P. Dean, et al., Opt. Express 16, 5997 (2008).  (a) (b) Fig. 1 (a) 2.6 THz self-mixing interferometry image of a scalpel blade at 10.5 m scanning-range. (b) Diffuse-reflectance spectra of a range of powders, at 3–3.4 THz. 

Detection of concealed weapons and characterisation of crystalline powders using terahertz quantum cascade lasers

Detection of concealed weapons and characterisation of crystalline powders using terahertz quantum cascade lasers

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