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Sensors 2013, 13(3), 3331-3340; doi:10.3390/s130303331

THz QCL-Based Cryogen-Free Spectrometer for in Situ Trace Gas Sensing

1,* , 1
1 CNR, Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI) 50019, Italy 2 Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK 3 NEST, CNR, Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa 56127, Italy
* Author to whom correspondence should be addressed.
Received: 3 January 2013 / Revised: 2 March 2013 / Accepted: 8 March 2013 / Published: 11 March 2013
(This article belongs to the Special Issue Laser Sensing and Imaging)
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We report on a set of high-sensitivity terahertz spectroscopy experiments making use of QCLs to detect rotational molecular transitions in the far-infrared. We demonstrate that using a compact and transportable cryogen-free setup, based on a quantum cascade laser in a closed-cycle Stirling cryostat, and pyroelectric detectors, a considerable improvement in sensitivity can be obtained by implementing a wavelength modulation spectroscopy technique. Indeed, we show that the sensitivity of methanol vapour detection can be improved by a factor ≈ 4 with respect to standard direct absorption approaches, offering perspectives for high sensitivity detection of a number of chemical compounds across the far-infrared spectral range.
Keywords: terahertz spectroscopy; quantum cascade lasers; trace gas sensing terahertz spectroscopy; quantum cascade lasers; trace gas sensing
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Consolino, L.; Bartalini, S.; Beere, H.E.; Ritchie, D.A.; Vitiello, M.S.; De Natale, P. THz QCL-Based Cryogen-Free Spectrometer for in Situ Trace Gas Sensing. Sensors 2013, 13, 3331-3340.

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