Abstract
A dual-gas photoacoustic spectroscopy (PAS) sensor based on wavelength modulation spectroscopy (WMS) was developed and experimentally demonstrated. Distributed feedback (DFB) laser diodes, emitting at 1512 and 1653 nm, were utilized as the excitation sources for the simultaneous measurement of NH3 and CH4, respectively. The PAS signal was excited by modulating the DFB laser at the first longitudinal resonant frequency of a cylindrical acoustic resonator. Absorption lines for NH3 and CH4 were simultaneously recorded during one frequency scan of the DFB lasers without using any optical switch. The interference of NH3 and CH4 on each other was investigated for accurate detection. The limits of detection (LoDs) of the PAS sensor for NH3 and CH4 for an integration time of 100 s were determined to be 0.1 and 0.3 ppm, respectively. The present PAS sensor provides a new scheme for multi-gas analysis with the advantages of cost-effectiveness, a simple structure and multi-wavelength operation.
Highlights
Various types of optical absorption spectroscopy—including photoacoustic spectroscopy [7,8], tunable diode laser-absorption spectroscopy (TDLAS) [9,10,11,12,13] and cavity-enhanced absorption spectroscopy (CEAS) [15]—are commonly used for trace gas analysis due to their advantages of noninvasive direct measurement and high sensitivity
We present a compact wavelength modulation photoacoustic spectroscopy for the simultaneous measurement of CH4 and NH3 based on a single acoustic resonator using two Distributed feedback (DFB) lasers emitting at 1512 and 1653 nm
InInthis we proposed a aPAS-based dual-gas detection method, which combines twoDFB
Summary
Various types of optical absorption spectroscopy—including photoacoustic spectroscopy [7,8], tunable diode laser-absorption spectroscopy (TDLAS) [9,10,11,12,13] (that could be combined with other hyperspectral imaging methods [14]) and cavity-enhanced absorption spectroscopy (CEAS) [15]—are commonly used for trace gas analysis due to their advantages of noninvasive direct measurement and high sensitivity. Multi-gas analysis using optical absorption spectroscopy requires either a broadband source (such as a light-emitting diode (LED)) [16], or widely tunable laser sources [17,18]
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