Title: Mid-infrared sensing of CO at saturated absorption conditions using intracavity quartz-enhanced photoacoustic spectroscopy
Language: English
Authors: Hayden, Jakob 
Baumgartner, Bettina  
Waclawek, Johannes P. 
Lendl, Bernhard  
Category: Research Article
Issue Date: 2019
Journal: Applied Physics B
ISSN: 1432-0649
The sensitivity of quartz-enhanced photoacoustic spectroscopy (QEPAS) can be drastically increased using the power enhancement in high-finesse cavities. Here, low noise resonant power enhancement to 6.3 W was achieved in a linear Brewster window cavity by exploiting optical feedback locking of a quantum cascade laser. The high intracavity intensity of up to 73 W mm−2 in between the prongs of a custom tuning fork resulted in strong optical saturation of CO at 4.59 µm. Saturated absorption is discussed theoretically and experimentally for photoacoustic measurements in general and intracavity QEPAS (I-QEPAS) in particular. The saturation intensity of CO’s R9 transition was retrieved from power-dependent I-QEPAS signals. This allowed for sensing CO independently from varying degrees of saturation caused by absorption induced changes of intracavity power. Figures of merit of the I-QEPAS setup for sensing of CO and H2O are compared to standard wavelength modulation QEPAS without cavity enhancement. For H2O, the sensitivity was increased by a factor of 230, practically identical to the power enhancement, while the sensitivity gain for CO detection was limited to 57 by optical saturation.
DOI: 10.1007/s00340-019-7260-6
Library ID: AC15533563
URN: urn:nbn:at:at-ubtuw:3-7794
Organisation: E164 - Institut für Chemische Technologien und Analytik 
Publication Type: Article
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