Photoacoustic spectroscopy, a powerful tool for gas analysis, typically uses bulky gas cells and discrete microphones. Here we exploit light-gas-acoustic interaction in a gas-filled anti-resonant hollow-core-fiber (AR-HCF) to demonstrate photoacoustic Brillouin spectroscopy (PABS). Pump absorption of gas molecules excites the acoustic resonances of the fiber, which modulates the phase of a probe beam propagating in the fiber. Detection of the phase modulation enables spectroscopic characterization of gas species and concentration as well as the fiber microstructure. Studying the acoustic resonances allows us to characterize the longitudinal inhomogeneity of the fiber microstructure. By tuning the pump modulation frequency to a wine-glass-like capillary mode of a 30-cm-long AR-HCF and the pump wavelength across a gas absorption line, we demonstrate detection of acetylene at the parts-per-billion level. PABS has great potential for high sensitivity gas sensing and non-invasive fiber characterization.

中文翻译：

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充气反共振中空光纤的光声布里渊光谱

光声光谱法是一种强大的气体分析工具，通常使用笨重的气室和分立的传声器。在这里，我们利用充气反共振空心纤维（AR-HCF）中的光-气-声相互作用来证明光声布里渊光谱（PABS）。气体分子的泵浦吸收激发了光纤的声共振，从而调制了在光纤中传播的探测光束的相位。通过检测相位调制，可以对气体种类和浓度以及纤维微结构进行光谱表征。对声共振的研究使我们能够表征纤维微结构的纵向不均匀性。通过将泵浦调制频率调整为30厘米长的AR-HCF的类似酒杯的毛细管模式，并将泵浦波长跨过气体吸收线，我们证明了以十亿分之一的水平检测到乙炔。PABS在高灵敏度气体传感和非侵入性光纤表征方面具有巨大潜力。