Abstract
A new approach for Quartz Enhanced Photoacoustic Spectroscopy is presented, based on an acoustic excitation from the outside of the prongs of a quartz tuning fork, to increase the sensitivity of the sensor. For this purpose, we introduce a monolithic acoustic double-resonator (double-mR) in a T-shape configuration, using 3D printing. It was modelized and experimentally characterized using a 1392 nm distributed feedback laser diode, targeting a water vapor absorption line. The setup showed a two-factor enhancement of the signal, compared to a classical off-beam QEPAS approach and confirmed the strong interest of photolithographic printing techniques for acoustic developments.
Highlights
Gas sensing is strongly demanding on sensitive, selective, and efficient techniques, to be implemented on laboratories experiments, environmental, medical, or industrial pur-poses
Photoacoustic spectroscopy relies on light absorption, through a specific gaseous species, when an absorption line corresponds to the emitted wavelength of a source
4.4.Conclusions noveldesign designwas was proposed, proposed,using using22 mRs mRsin inaa monolithic monolithicsetup, setup,to toincrease increase the the AAnovel acoustic pressure actuating on the two external sides of QTF prongs
Summary
Gas sensing is strongly demanding on sensitive, selective, and efficient techniques, to be implemented on laboratories experiments, environmental, medical, or industrial pur-poses. Since its invention in 2002 [1], Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) demonstrated many advantages among techniques based on tunable sources and indirect gas absorption detection. While the source intensity is modulated, the light absorption is modulated as well, and gives rise to a localized sound wave at the modulation frequency. This indirect photonic effect is called the photoacoustic effect, which has been exploited for years [3], using resonant acoustic cells and microphones for sound sensing. In QEPAS, the sound wave interacts with a mechanical transducer (a quartz tuning fork or QTF), leading to a piezoelectric current. Thanks to the very high quality factor of the QTF (~10,000 at atmospheric pressure), it is unnecessary to use any resonant acoustic cell, as done in classical microphone photoacoustics sensing
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