Abstract
Quartz-enhanced photoacoustic spectroscopy (QEPAS) is an improvement of the conventional microphone-based photoacoustic spectroscopy. In the QEPAS technique, a commercially available millimeter-sized piezoelectric element quartz tuning fork (QTF) is used as an acoustic wave transducer. With the merits of high sensitivity and selectivity, low cost, compactness, and a large dynamic range, QEPAS sensors have been applied widely in gas detection. In this review, recent developments in state-of-the-art QEPAS-based trace gas sensing technique over the past five years are summarized and discussed. The prospect of QEPAS-based gas sensing is also presented.
Highlights
Photoacoustic spectroscopy (PAS) is an indirect absorption spectroscopy
When excitation sources with bad beam quality such as light-emitting diodes (LEDs), vertical cavity surface emitting lasers (VCSELs), and terahertz (Thz) quantum cascade laser (QCL) are used in Quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors, the large beam diameter and divergence angle make the light beam unable to pass through the micro-resonators and the 300 μm gap between the two prongs of usually used standard quartz tuning fork (QTF) totally, resulting in obvious optical noise
Compared to other absorption spectroscopy such as as tunable diode laser absorption spectroscopy (TDLAS), a distinct advantage of the sensor tunable diode laser absorption spectroscopy (TDLAS), a distinct advantage of the sensor is is that its performance can be improved when the output power of the excitation laser source is that its performance can be improved when the output power of the excitation laser source is increased
Summary
Photoacoustic spectroscopy (PAS) is an indirect absorption spectroscopy. It is based on the photoacoustic effect, which was first discovered by Alexander Graham Bell in 1880 [1]. From Equation (1), it can be seen that the signal amplitude of PAS sensor is inversely proportional to the resonance frequency of the photo-acoustic cell. If the resonance frequency is too low, it makes the PAS sensor more sensitive to 1/f noise, environmental noise, and sample gas flow noise. It will result in a low signal-to-noise ratio (SNR) for the PAS sensor [3]. For the microphone-based PAS, the low value of Q factor (
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