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Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Languages: English
Types: Article
We demonstrate diffuse-reflectance (DR) spectroscopy of powders using a discretely-tunable terahertz-frequency quantum cascade laser (THz QCL) with a heterogeneous active region. DR signatures were obtained at frequencies of 3.06, 3.21, 3.28 and 3.35 THz, and the relative absorption coefficients were inferred at each frequency using a Kubelka–Munk (KM) scattering model. The spectral lineshapes reproduce the absolute Beer–Lambert (BL) absorption spectra of a range of materials, which were also measured using conventional transmission-mode THz time-domain spectroscopy. It is shown that the DR technique works reliably for materials that include pharmaceutical compounds and foodstuffs, with BL absorption coefficients in the range 2–10 mm−1. This method is potentially suitable for automated material identification, without any requirement for a priori knowledge of the refractive index or scattering properties of the sampled material.
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    • Paul Dean received the M.Phys. (Hons.) degree in physics in 2001 and the Ph.D. degree in laser physics in 2005, both from the University of Manchester, Manchester, U.K. In 2005, he was appointed as a Post-Doctoral Research Associate at the Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Leeds, U.K., and as a University Research Fellow in 2011. His research interests include terahertz optoelectronics, quantum cascade lasers, and terahertz imaging techniques.
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