Fraunhofer-Gesellschaft

Publica

Hier finden Sie wissenschaftliche Publikationen aus den Fraunhofer-Instituten.

Comparison of laser-based photoacoustic and optical detection of methane

 
: Strahl, Thomas; Herbst, Johannes; Maier, Eric; Rademacher, Sven; Weber, Christian; Pernau, Hans-Fridtjof; Lambrecht, Armin; Wöllenstein, Jürgen

:
Fulltext ()

Journal of sensors and sensor systems : JSSS 10 (2021), No.1, pp.25-35
ISSN: 2194-8771
ISSN: 2194-878X
Bundesministerium für Bildung und Forschung BMBF (Deutschland)
E! 9727-MASUM; MASUM
Marine Sulfur Monitor
English
Journal Article, Electronic Publication
Fraunhofer IPM ()
methane; Laser Spectroscopy; photoacoustic spectroscopy; Direct Absorption Spectroscopy

Abstract
The measurement of low methane (CH4) concentrations is a key objective for safety of industrial and public infrastructures and in environmental research. Laser spectroscopy is best suited for this purpose because it offers high sensitivity, selectivity, dynamic range, and a fast measurement rate. The physical basis of this technique is infrared absorption of molecular gases. Two detection schemes – direct absorption spectroscopy (DAS) and photoacoustic spectroscopy (PAS) – are compared at three wavelength regions in the near-infrared (NIR), mid-wavelength (MWIR), and long-wavelength (LWIR) infrared ranges. For each spectral range a suitable semiconductor laser is selected and used for both detection techniques: a diode laser (DL), an interband cascade laser (ICL), and a quantum cascade laser (QCL) for NIR, MWIR and LWIR, respectively. For DAS short absorption path lengths comparable to the cell dimensions of the photoacoustic cell for PAS are employed. We show that for DAS the lowest detection limit can be achieved in the MWIR range with noise-equivalent concentrations (NECs) below 10 ppb. Using PAS, lower detection limits and higher system stabilities can be reached compared to DAS, especially for long integration times. The lowest detection limit for PAS is obtained in the LWIR with a NEC of 7 ppb. The different DAS and PAS configurations are discussed with respect to potential applications.

: http://publica.fraunhofer.de/documents/N-624978.html