A compact integrated dual-spectroscopy gas detection structure based on QEPAS and QEPTS using a QTF

Abstract

If the acetylene (C2H2) content in the oxygen production device exceeds the standard, it is highly susceptible to explosion. It is necessary to detect C2H2 gas and reach the detection limit of ppm. A novel single quartz tuning fork (QTF) compact integrated dual-spectroscopy gas detection structure based on quartz-enhanced photoacoustic spectroscopy (QEPAS) and quartz-enhanced photothermal spectroscopy (QEPTS) was designed for improving detection intensity and reducing sensor size. The detection structure (40 mm × 90 mm × 50 mm) includes gas buffer, gas detection structure, and preamplifier circuit. In the structure, an off-beam acoustic micro-resonator (AMR) was used to enhance the photoacoustic signal. After passing the AMR, the laser beam was turned back by the right-angle prism and incident on the side of the QTF fork again to generate the photothermal signal. The silver layer on the QTF surface was chemically etched to further enhance the photothermal signal. For the traditional off-beam photoacoustic excitation, the photothermal signal is excited by the way of laser retracting. The superposition of the dual-spectroscopy detection technology on a single QTF is realized. And the structure is finely integrated which is convenient to carry and measure. Under the same conditions, photoacoustic signal, photothermal signal and dual-spectroscopy signal were measured respectively. The measured dual-spectroscopy signal was approximately the superposition value of photoacoustic signal and photothermal signal, which showed the effective signal lifting effect. With C2H2 as the target gas, the experimental results showed that the signal value of the dual-spectroscopy structure was 1.94 times that of QEPAS structure, 2.18 times that of QEPTS structure. And the minimum detection limit at atmospheric pressure was 6.64 ppm. The integrated dual-spectroscopy structure was compact, and was suitable for small space measurement, mobile measurement, and other fields.