A neotype fiber optic photoacoustic gas sensor with overlapping phantom spots based multi-pass is proposed, which greatly improves the reflection times and the length of gas absorption path. Moreover, the detection accuracy of photoacoustic spectroscopy (PAS) system is independent of the optical interference effect caused by overlapping spots, which is different from tunable diode laser absorption spectroscopy (TDLAS) technology. A mathematical model including light beam motion space, spot size and overlap discrimination of multi-pass structure based on overlapping phantom spots is established. The incident light is reflected up to dozens of times in the resonator with a diameter of only 8 mm. The emergent light does not need to converge on a photodetector, which reduces the difficulty of adjusting the optical path and promotes the realization of overlapping phantom spots. The experimental results show that the amplitude of photoacoustic signal is improved by about 40 times compared with the single spot structure. Appling high-sensitivity optical fiber cantilever to detect the sound pressure signal. The detection limit of CH gas reaches 8.2 ppt. The normalized noise equivalent absorption (NNEA) coefficient of the gas sensor is achieved to be 9.3×10 cmWHz.

中文翻译：

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通过具有重叠幻斑的多通道池增强的光纤光声气体传感器

提出了一种基于多通道重叠幻斑的新型光纤光声气体传感器，大大提高了反射次数和气体吸收路径的长度。而且，光声光谱（PAS）系统的检测精度与重叠光斑引起的光学干涉效应无关，这与可调谐二极管激光吸收光谱（TDLAS）技术不同。建立了基于重叠幻斑的多通道结构的包括光束运动空间、光斑尺寸和重叠判别的数学模型。入射光在直径仅为8毫米的谐振腔内反射多达数十次。出射光无需汇聚到光电探测器上，降低了光路调节难度，促进了重叠幻斑的实现。实验结果表明，与单光斑结构相比，光声信号幅度提高了约40倍。采用高灵敏度光纤悬臂梁检测声压信号。 CH气体的检测限达到8.2 ppt。该气体传感器的归一化噪声等效吸收（NNEA）系数达到9.3×10 cmWHZ。