Yang Minghong, Liu Zhixiong, Xiong Lingxi, Nie Qilu, Wang Yingying, Gao Shoufei, Cheng Mengen, Yang Dexun, Pei Shilong, Guo Donglai
Opt Express. 2024 Jan 29;32(3):4093-4101. doi: 10.1364/OE.509758.
Antiresonant hollow-core fiber (AR-HCF) exhibits unprecedented optical performance in low transmission attenuation, broad transmission bandwidth, and single spatial mode quality. However, due to its lower numerical aperture, when utilizing the Fiber-Enhanced Raman Spectroscopy (FERS) principle for gas detection, the efficiency of AR-HCF in collecting Raman signals per unit length is significantly lower than that of hollow-core photonic crystal fiber. Nonetheless, AR-HCF effectively suppresses higher-order modes and offers bandwidth in hundreds of nanometers. By increasing the length of AR-HCF, its advantages can be effectively harnessed, leading to a considerable enhancement in the system's ability for low-concentration gas detection. We combine the nodeless antiresonant hollow-core fiber and Raman spectroscopy for enhanced Raman gas sensing in a forward scattering measurement configuration to investigate the attenuation behavior of the silica background signals. The silica background attenuation behavior enables the low baseline of the gas Raman spectroscopy and extends the integration time of the system. In addition, a convenient spatial filtering method is investigated. A multimode fiber with a suitable core diameter was employed to transmit the signal so that the fiber end face plays the role of pinhole, thus filtering the silica signal and reducing the baseline. The natural isotopes CO, CO, and COO in ambient air can be observed using a 5-meter-long AR-HCF at 1 bar with a laser output power of 1.8 W and an integration time of 300 seconds. Limits of detection have been determined to be 0.5 ppm for CO and 1.2 ppm for CO, which shows that the FERS with AR-HCF has remarkable potential for isotopes and multigas sensing.
反谐振空芯光纤（AR-HCF）在低传输损耗、宽传输带宽和单空间模式质量方面展现出前所未有的光学性能。然而，由于其数值孔径较低，在利用光纤增强拉曼光谱（FERS）原理进行气体检测时，AR-HCF每单位长度收集拉曼信号的效率显著低于空芯光子晶体光纤。尽管如此，AR-HCF能有效抑制高阶模式并提供数百纳米的带宽。通过增加AR-HCF的长度，可以有效利用其优势，从而显著提高系统对低浓度气体的检测能力。我们将无节点反谐振空芯光纤与拉曼光谱相结合，在前向散射测量配置中实现增强的拉曼气体传感，以研究二氧化硅背景信号的衰减行为。二氧化硅背景的衰减行为能够实现气体拉曼光谱的低基线，并延长系统的积分时间。此外，还研究了一种便捷的空间滤波方法。采用具有合适芯径的多模光纤来传输信号，使光纤端面起到针孔的作用，从而滤除二氧化硅信号并降低基线。在1巴压力、激光输出功率为1.8瓦且积分时间为300秒的条件下，使用5米长的AR-HCF可以观测到环境空气中的天然同位素CO、CO和COO。已确定CO的检测限为0.5 ppm，CO的检测限为1.2 ppm，这表明基于AR-HCF的FERS在同位素和多气体传感方面具有显著潜力。
