Terahertz active photonic crystals for condensed gas sensing

• Published in: Sensors (Basel, Switzerland) Vol. 11; no. 6; pp. 6003 - 6014
• Main Authors: Benz, Alexander, Deutsch, Christoph, Brandstetter, Martin, Andrews, Aaron M, Klang, Pavel, Detz, Hermann, Schrenk, Werner, Strasser, Gottfried, Unterrainer, Karl
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.06.2011; Molecular Diversity Preservation International (MDPI)
• Subjects: active resonator; Algorithms; Argon - chemistry; Biosensing Techniques; Equipment Design; Gases - analysis; Lasers; Optical Devices; optical microsensor; Oxygen - chemistry; Photons; Quantum dots; Quantum Theory; quantum-cascade laser; Radiation; Refractometry; Reproducibility of Results; Sensors; terahertz; Terahertz Radiation; Austria; optical microsensor; active resonator; quantum-cascade laser; terahertz
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s110606003

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(-3) times the center lasing frequency. The minimum detectable refractive index change is 1.6 × 10(-5) RIU.