Sensitive Photoacoustic Gas Sensor for NO_x Detection Using Hybrid Resonant Modes

As a typical environmental pollutant and biomarker, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{N}\mathrm{O}_{\mathrm{x}}$</tex> has long been a target of interest for the development of gas sensors [1]. Photoacoustic spectroscopy (PAS), as a fingerprint-based absorption spectroscopic technique, has become a promising method for the detection of gas components owing to its high accuracy, fast response time, and high selectivity. The classical way to enhance the photoacoustic signal is to use an acoustic resonance cell, where the resonance modes are excited to amplify the signal [2]. However, resonance cell-based multi-gas sensors usually face challenges such as difficult time/frequency separation, poor signal-to-noise ratio for higher-order modes, and large sample gas consumption. It was reported to imporve the optical absorption path by utilizing a spherical cell [3].