Abstract
We have designed and fabricated a custom quartz tuning fork (QTF) with a reduced fundamental frequency; a larger gap between the prongs; and the best quality factor in air at atmospheric conditions ever reported, to our knowledge. Acoustic microresonators have been added to the QTF in order to enhance the sensor sensitivity. We demonstrate a normalized noise equivalent absorption (NNEA) of 3.7 × 10−9 W.cm−1.Hz−1/2 for CO2 detection at atmospheric pressure. The influence of the inner diameter and length of the microresonators has been studied, as well as the penetration depth between the QTF’s prongs. We investigated the acoustic isolation of our system and measured the Allan deviation of the sensor.
Highlights
Detection of hazardous chemicals and greenhouse gases is one among the many challenges of our century
6 ofthe characterized the effect of the cavity on the quartz tuning fork (QTF), we study the influence of geometry of the microresonators on the quality factor when using such a cavity
Owing to the wider gap between the QTF’s prongs (2 mm) than for standard QTFs, a better sensitivity and less experimental difficulties are expected with the use of larger laser beams in the mid-infrared
Summary
Detection of hazardous chemicals and greenhouse gases is one among the many challenges of our century. The sensitivity of a photoacoustic detector can be qualified by a figure of merit, called normalized noise equivalent absorption (NNEA) It represents the minimum detectable absorption, independent from the laser power, the electrical bandwidth, and the absorption coefficient of the gas. A new technique called quartz enhanced photoacoustic spectroscopy (QEPAS) was introduced in 2002 [2], providing a good tradeoff between compactness and sensitivity of the acoustic detector, as well as good acoustic isolation from the environment This technique involves the generation of a pressure wave through gas excitation with an amplitude- or wavelength -modulated laser and its detection with a quartz tuning fork (QTF), usually complemented by longitudinal acoustic resonators
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