{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,24]],"date-time":"2026-03-24T08:37:43Z","timestamp":1774341463608,"version":"3.50.1"},"reference-count":32,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2013,3,11]],"date-time":"2013-03-11T00:00:00Z","timestamp":1362960000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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 \u2248 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.<\/jats:p>","DOI":"10.3390\/s130303331","type":"journal-article","created":{"date-parts":[[2013,3,11]],"date-time":"2013-03-11T12:14:24Z","timestamp":1363004064000},"page":"3331-3340","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":54,"title":["THz QCL-Based Cryogen-Free Spectrometer for in Situ Trace Gas Sensing"],"prefix":"10.3390","volume":"13","author":[{"given":"Luigi","family":"Consolino","sequence":"first","affiliation":[{"name":"CNR, Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI) 50019, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8338-748X","authenticated-orcid":false,"given":"Saverio","family":"Bartalini","sequence":"additional","affiliation":[{"name":"CNR, Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI) 50019, Italy"}]},{"given":"Harvey","family":"Beere","sequence":"additional","affiliation":[{"name":"Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK"}]},{"given":"David","family":"Ritchie","sequence":"additional","affiliation":[{"name":"Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK"}]},{"given":"Miriam","family":"Vitiello","sequence":"additional","affiliation":[{"name":"CNR, Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI) 50019, Italy"},{"name":"NEST, CNR, Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12,  Pisa 56127, Italy"}]},{"given":"Paolo","family":"De Natale","sequence":"additional","affiliation":[{"name":"CNR, Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI) 50019, Italy"}]}],"member":"1968","published-online":{"date-parts":[[2013,3,11]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"28","DOI":"10.1364\/OL.7.000028","article-title":"Frequency-modulation spectroscopy with a pulsed dye laser","volume":"7","author":"Gallagher","year":"1982","journal-title":"Opt. 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