A proof-of-concept gas sensor based on a miniaturized and integrated fiber-optic photoacoustic detection module was introduced and demonstrated for the purpose of developing a custom tuning-fork (TF)-enhanced photoacoustic gas sensor. Instead of piezoelectric quartz tuning fork (QTF) in conventional quartz-enhanced photoacoustic spectroscopy (QEPAS), a low-cost custom aluminum alloy TF fabricated by mechanical processing was employed as a photoacoustic transducer and the vibration of TF was measured by fiber-optic Fabry-Pérot (FP) interferometer (FPI). The mechanical processing-based TF design scheme greatly increases the flexibility of the TF design with respect to the complex and expensive manufacture process of custom QTFs, and thus it can be better exploited to detect gases with slow vibrational-translational (V-T) relaxation rates and combine with light sources with poor beam quality. The resonance frequency and the quality factor of the designed custom TF at atmospheric pressure were experimentally determined to be 7.3 kHz and 4733, respectively. Dual-prong differential measurement method was proposed to double the photoacoustic signal and suppress the external same-direction noise. After detailed optimizing and investigating for the operating parameters by measuring HO, the feasibility of the developed sensor for gas detection was demonstrated with a HO minimum detection limit (MDL) of 1.2 ppm, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 3.8 × 10 cm W/Hz, which are better than the QTF-based photoacoustic sensors. The proposed gas sensing approach combined the advantages of QEPAS and fiber-optic sensing, which can greatly expand the application domains of PAS-based gas sensors.

中文翻译：

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基于机械加工的集成音叉双爪差动测量小型化高灵敏度光纤光声气体传感器

介绍并演示了一种基于小型化集成光纤光声检测模块的概念验证气体传感器，旨在开发定制音叉 (TF) 增强型光声气体传感器。采用机械加工制造的低成本定制铝合金TF作为光声换能器，代替传统石英增强光声光谱（QEPAS）中的压电石英音叉（QTF），并通过光纤法布里测量TF的振动-佩罗（FP）干涉仪（FPI）。基于机械加工的TF设计方案大大提高了TF设计的灵活性，相对于定制QTF复杂且昂贵的制造过程，因此可以更好地利用它来检测具有慢振动平移（VT）弛豫率的气体和与光束质量较差的光源结合使用。经实验确定，所设计的定制TF在大气压下的谐振频率和品质因数分别为7.3 kHz和4733。提出双管脚差分测量方法，将光声信号加倍并抑制外部同向噪声。通过测量 H2O 对操作参数进行详细优化和研究后，证明了所开发的传感器用于气体检测的可行性，H2O 最低检测限 (MDL) 为 1.2 ppm，对应于归一化噪声等效吸收 (NNEA) 系数为 3.8 × 10 cm W/Hz，优于基于 QTF 的光声传感器。所提出的气体传感方法结合了QEPAS和光纤传感的优点，可以极大地扩展基于PAS的气体传感器的应用领域。