A hollow-core antiresonant fiber-based pressure-compensated wavelength modulation spectroscopy system for acetylene detection

This study reports a compact acetylene (C 2 H 2 ) detection system based on tunable diode laser absorption spectroscopy (TDLAS) using a 92-cm hollow-core antiresonant fiber (HC-ARF). Both direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) were conducted independently to measure the strong absorption line at 6523.88 cm −1 . DAS measurement exhibits significant interference fringe noise, resulting in a noise equivalent absorption (NEA) coefficient of 3.2 × 10 -4 cm −1 . In contrast, WMS achieves a noise equivalent concentration (NEC) of 1.26 ppm at an integration time of 24 s, corresponding to a NEA coefficient of 1.3 × 10 -6 cm −1 . Pressure tests indicate that variations in gas pressure affect the full width at half maximum (FWHM) of the absorption line, subsequently altering the amplitude of the second-harmonic (2 f ) signal. To address this issue, a pressure-compensation algorithm is developed. Following compensation, pressure-related concentration deviations are reduced from − 25.9% to + 7.9% before compensation to within ± 2.2% across the pressure range of 60–140 kPa. These findings demonstrate that HC-ARF-based TDLAS provides sensitive, fast, and pressure-adaptive C 2 H 2 detection, and the compensation algorithm is applicable to other gases and various hollow-core fiber-based laser spectroscopy systems.