Abstract
A quartz enhanced photoacoustic spectroscopy (QEPAS) sensor system based on an elliptical laser beam for trace gas detection was demonstrated. A Powell lens was exploited to shape the circular laser beam into an elliptical laser beam for the full utilization of the quartz tuning fork (QTF) prong spacing. Based on the finite element modeling (FEM) simulation software COMSOL, the distribution of acoustic pressure on QTF prongs with different beam shapes was simulated theoretically. The experimental results showed that the QEPAS signal based on the elliptical laser beam had a 1.4-fold improvement compared with the circular laser beam, resulting in a minimum detection limit of 418.6 ppmv and the normalized noise equivalent absorption (NNEA) of 1.51 × 10−6 cm−1 W/√Hz at atmospheric pressure.
Highlights
Trace gas detection techniques play an important role in the fields of environment, industry, aerospace, and medical technology [1,2,3,4,5]
Considering that the photoacoustic signal from Quartz-enhanced photoacoustic spectroscopy (QEPAS) system is proportional to the number of gas molecules which are excited to a high energy state by absorbing photons from an excitation source in unit time, the inner surface areas of the quartz tuning fork (QTF) prongs are underutilized with such a small circular laser spot
We report a QEPAS sensor based on a Powell lens to compare the effect of circular beam and strip beam illuminating the QTF prong spacing
Summary
Trace gas detection techniques play an important role in the fields of environment, industry, aerospace, and medical technology [1,2,3,4,5]. Considering that the photoacoustic signal from QEPAS system is proportional to the number of gas molecules which are excited to a high energy state by absorbing photons from an excitation source in unit time, the inner surface areas of the QTF prongs are underutilized with such a small circular laser spot. We report a QEPAS sensor based on a Powell lens to compare the effect of circular beam and strip beam illuminating the QTF prong spacing. The work verified the feasibility of the combination of the QEPAS technique and the diverging laser sources or light sources with broad emitting stripes, which means that we do not need to waste excessive time and money in circularizing laser beams This result provides the premise for the application of QEPAS sensors based on novel laser sources with a strip laser beam
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