title: Terahertz active photonic crystals for condensed gas sensing.
abstract: 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.
authors.affiliation: Photonics Institute and Center for Micro- and Nanostructures, Vienna University of Technology, Vienna, Austria. alexander.benz@tuwien.ac.at
authors.forename: Alexander
authors.initials: A
authors.lastname: Benz
authors.forename: Christoph
authors.initials: C
authors.lastname: Deutsch
authors.forename: Martin
authors.initials: M
authors.lastname: Brandstetter
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Andrews
authors.forename: Pavel
authors.initials: P
authors.lastname: Klang
authors.forename: Hermann
authors.initials: H
authors.lastname: Detz
authors.forename: Werner
authors.initials: W
authors.lastname: Schrenk
authors.forename: Gottfried
authors.initials: G
authors.lastname: Strasser
authors.forename: Karl
authors.initials: K
authors.lastname: Unterrainer
mesh_terms: D000465:Algorithms; D001128:Argon / Q000737:chemistry; D015374:Biosensing Techniques; D004867:Equipment Design; D005740:Gases / Q000032:analysis*; D007834:Lasers; D055096:Optical Devices; D010100:Oxygen / Q000737:chemistry; D017785:Photons; D011789:Quantum Theory; D012031:Refractometry; D015203:Reproducibility of Results; D055053:Terahertz Radiation
chemical_list: D005740:Gases; D001128:Argon; D010100:Oxygen