{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,5]],"date-time":"2026-03-05T16:07:07Z","timestamp":1772726827306,"version":"3.50.1"},"reference-count":57,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2011,6,3]],"date-time":"2011-06-03T00:00:00Z","timestamp":1307059200000},"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>The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection scheme. Here, we present an optical sensor based on active photonic crystals (PhCs), i.e., the pillars are fabricated directly from an active THz quantum-cascade laser medium. The individual pillars are pumped electrically leading to laser emission at cryogenic temperatures. There is no need to couple light into the resonant structure because the PhC itself is used as the light source. An injected gas changes the resonance condition of the PhC and thereby the laser emission frequency. We achieve an experimental frequency shift of 10\u22123 times the center lasing frequency. The minimum detectable refractive index change is 1.6 \u00d7 10\u22125 RIU.<\/jats:p>","DOI":"10.3390\/s110606003","type":"journal-article","created":{"date-parts":[[2011,6,3]],"date-time":"2011-06-03T14:58:56Z","timestamp":1307113136000},"page":"6003-6014","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":35,"title":["Terahertz Active Photonic Crystals for Condensed Gas Sensing"],"prefix":"10.3390","volume":"11","author":[{"given":"Alexander","family":"Benz","sequence":"first","affiliation":[{"name":"Photonics Institute and Center for Micro- and Nanostructures, Vienna University of Technology, Gusshausstrasse 29\/387, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Christoph","family":"Deutsch","sequence":"additional","affiliation":[{"name":"Photonics Institute and Center for Micro- and Nanostructures, Vienna University of Technology, Gusshausstrasse 29\/387, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Martin","family":"Brandstetter","sequence":"additional","affiliation":[{"name":"Photonics Institute and Center for Micro- and Nanostructures, Vienna University of Technology, Gusshausstrasse 29\/387, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5790-2588","authenticated-orcid":false,"given":"Aaron M.","family":"Andrews","sequence":"additional","affiliation":[{"name":"Institute of Solid-State Electronics and Center for Micro- and Nanostructures, Vienna University of Technology, Floragasse 7\/362, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Pavel","family":"Klang","sequence":"additional","affiliation":[{"name":"Institute of Solid-State Electronics and Center for Micro- and Nanostructures, Vienna University of Technology, Floragasse 7\/362, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4167-3653","authenticated-orcid":false,"given":"Hermann","family":"Detz","sequence":"additional","affiliation":[{"name":"Institute of Solid-State Electronics and Center for Micro- and Nanostructures, Vienna University of Technology, Floragasse 7\/362, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Werner","family":"Schrenk","sequence":"additional","affiliation":[{"name":"Institute of Solid-State Electronics and Center for Micro- and Nanostructures, Vienna University of Technology, Floragasse 7\/362, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0147-0883","authenticated-orcid":false,"given":"Gottfried","family":"Strasser","sequence":"additional","affiliation":[{"name":"Institute of Solid-State Electronics and Center for Micro- and Nanostructures, Vienna University of Technology, Floragasse 7\/362, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Karl","family":"Unterrainer","sequence":"additional","affiliation":[{"name":"Photonics Institute and Center for Micro- and Nanostructures, Vienna University of Technology, Gusshausstrasse 29\/387, Vienna, Austria"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2011,6,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"401","DOI":"10.1016\/j.optcom.2004.02.056","article-title":"Laser oscillations of resonance modes in a thin gain-doped ring-type cylindrical microcavity","volume":"235","author":"Moon","year":"2004","journal-title":"Opt. 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