Antiresonant fiber-enhanced Raman spectroscopy gas sensing with 1†ppm sensitivity.

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 12C16O2, 13C16O2, and 12C18O16O 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 13C16O2 and 1.2 ppm for 12C16O2, which shows that the FERS with AR-HCF has remarkable potential for isotopes and multigas sensing.

Multicomponent Gas Sensing Fiber Probe System Based on Platinum Coated Capillary Enhanced Raman Spectroscopy.

This paper proposes a novel multicomponent gas-sensing optical fiber probe system. It utilizes a precisely engineered Platinum-coated capillary fabricated via Atomic Layer Deposition (ALD) technology as the core for enhanced Raman spectroscopy, marking the first application of ALD in creating such a structure for gas Raman sensing. The noble metal capillary gas Raman probe demonstrates a low detection limit of 55 ppm for CO2 with a 30 s exposure time and good repeatability in multicomponent gas sensing. The capillary exhibits excellent stability, environmental resistance, and a large core diameter, enabling a rapid gas exchange rate and making it suitable for practical applications.