Abstract
Acoustic microresonators were added to the recently developed multi-QTF based QEPAS spectrophone to enhance the signal amplitude. Two kinds of “on-beam” configurations were experimentally investigated in detail. The developed multi-QTF based “on-beam” spectrophone had a signal enhancement of 1.6 times compared with the traditional single QTF based “on-beam” spectrophone, with the approximate noise level. A normalized noise equivalent absorption coefficient (1σ) of 1.24 × 10−9 W·cm−1·Hz−1/2was obtained for water vapor detection at atmospheric pressure.
Highlights
Laser absorption spectroscopy for trace gas detection has gained considerable interest over the past decades
As a variation of PAS, quartz enhanced photoacoustic spectroscopy (QEPAS), by use of a quartz tuning fork (QTF) instead of a traditional microphone, is a booming technique for trace gas detection that has been widely used for environmental monitoring, industrial process control analysis, combustion processes, and detection of toxic and flammable gases, as well as explosives [5]
Multi-quartz enhanced photoacoustic spectroscopy (M-QEPAS) uses a pair of QTFs with similar resonance frequencies connected in parallel, instead of a single QTF in the traditional QEPAS spectrophone, to enhance the signal amplitude through coupling effect between the two QTFs [11]
Summary
Laser absorption spectroscopy for trace gas detection has gained considerable interest over the past decades. Two sophisticated QEPAS spectrophones with AmRs assembled in “on-beam” and “off-beam” configurations have been developed to improve the performance of bare-QTF based QEPAS sensors [9, 10]. Double acoustic microresonator quartz-enhanced photoacoustic spectroscopy which employed the spectrophone that consisted of a QTF and two sets of the “onbeam” AmRs was developed for optical signal addition and multigas rapid spectral measurement with a response time of 5 ms [1]. Multi-quartz enhanced photoacoustic spectroscopy (M-QEPAS) uses a pair of QTFs with similar resonance frequencies connected in parallel, instead of a single QTF in the traditional QEPAS spectrophone, to enhance the signal amplitude through coupling effect between the two QTFs [11]. The distance between the AmR and the QTF in the multiQTF based “on-beam” QEPAS spectrophone was optimized to obtain the maximum signal amplitude
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