{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,12]],"date-time":"2026-05-12T08:20:23Z","timestamp":1778574023303,"version":"3.51.4"},"reference-count":57,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2018,6,27]],"date-time":"2018-06-27T00:00:00Z","timestamp":1530057600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Agency for innovation by science and technology","award":["130036"],"award-info":[{"award-number":["130036"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>We employed a single-mode, widely tunable (~300 cm\u22121) external-cavity quantum cascade laser operating around 8 \u00b5m for broadband direct absorption spectroscopy and wavelength modulation spectroscopy where a modulation frequency of 50 kHz was employed with high modulation amplitudes of up to 10 GHz. Using a compact multipass cell, we measured the entire molecular absorption band of acetone at ~7.4 \u00b5m with a spectral resolution of ~1 cm\u22121. In addition, to demonstrate the high modulation dynamic range of the laser, we performed direct absorption (DAS) and second harmonic wavelength modulation spectroscopy (WMS-2f) of the Q-branch peak of acetone molecular absorption band (HWHM ~10 GHz) near 1365 cm\u22121. With WMS-2f, a minimum detection limit of 15 ppbv in less than 10 s is achieved, which yields a noise equivalent absorption sensitivity of 1.9 \u00d7 10\u22128 cm\u22121 Hz\u22121\/2.<\/jats:p>","DOI":"10.3390\/s18072050","type":"journal-article","created":{"date-parts":[[2018,6,27]],"date-time":"2018-06-27T11:02:05Z","timestamp":1530097325000},"page":"2050","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["Sensitive Spectroscopy of Acetone Using a Widely Tunable External-Cavity Quantum Cascade Laser"],"prefix":"10.3390","volume":"18","author":[{"given":"Faisal","family":"Nadeem","sequence":"first","affiliation":[{"name":"Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Julien","family":"Mandon","sequence":"additional","affiliation":[{"name":"Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Amir","family":"Khodabakhsh","sequence":"additional","affiliation":[{"name":"Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Simona M.","family":"Cristescu","sequence":"additional","affiliation":[{"name":"Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Frans J. M.","family":"Harren","sequence":"additional","affiliation":[{"name":"Trace Gas Research Facility, Molecular, and Laser Physics, Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2018,6,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"165","DOI":"10.1007\/s00340-007-2846-9","article-title":"Application of quantum cascade lasers to trace gas analysis","volume":"90","author":"Kosterev","year":"2008","journal-title":"Appl. Phys. B"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"012004","DOI":"10.1088\/0957-0233\/24\/1\/012004","article-title":"Optical gas sensing: A review","volume":"24","author":"Hodgkinson","year":"2013","journal-title":"Meas. Sci. 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