Analysis of CH₄, C₂H₆, C₂H₄, C₂H₂, H₂, CO, and H₂S by forward Raman scattering with a hollow‐core anti‐resonant fiber

Abstract

Fiber-enhanced Raman spectroscopy is applied actively for gas analysis. Hollow-core anti-resonant fibers (HC-ARFs) with low loss and low spatial overlap between core and cladding modes show the potential of low background. We integrated an HC-ARF into the Raman system, collected the forward scattering radiation with a lens-coupled imaging spectrometer, and filtered most of the background through selection of region of interest. The limits of detection (LODs) of this system were determined as 1.2 ppmÁbar for CH 4 , 2.9 ppmÁbar for C 2 H 6 , 1.6 ppmÁbar for C 2 H 4 , 2.7 ppmÁbar for C 2 H 2 , 13.8 ppmÁbar for H 2 , and 16.7 ppmÁbar for CO with the excitation laser of 200 mW and the exposure time of 60 s. In addition, the LOD was better than 2.5 ppmÁbar for H 2 S. By the detection of gas samples with the critical detectable concentration, it was proven that the estimated values of LOD from the preceding experimental results are reliable and the system had practical detectability. The gas samples we tested are relevant for multiple fields such as

Fluorescence Noise Eliminating Fiber-Enhanced Raman Spectroscopy for Simultaneous and Multiprocess Analysis of Intermediate Compositions for C2H2 and H2 Production

“…The excitation light will inevitably react with the HC-ARF glass components to generate spatial fluorescence noise that is circularly distributed around the Raman signal, and it will seriously affect the sensitivity and stability of multiprocess intermediate gas detection. To effectively filter out spatial fluorescence noise, an FNE combining pinhole spatial filtering and CCD digital filtering is proposed and verified by air detection (integration time of 30 s, measured pressure of 1 bar). Figure a shows the raw CCD image of the unfiltered air Raman signal, the horizontal spatial fluorescence noise is distributed on the upper and lower ends of the Raman signal on the CCD, and the vertical spatial fluorescence noise is parasitic in the CCD pixel row, where the nitrogen and oxygen Raman signals are located.…”

In-situ background-free Raman endoscope using double-cladding anti-resonant hollow-core fibers

“…Compared to other microstructured hollow-core fibers such as Kagome and photonic bandgap hollow core fibers, AR-HCFs offer a much wider low-loss transmission window and a broader tuning range of central wavelength, spanning from the deep ultraviolet to the mid-infrared. As a result, AR-HCFs have found applications in various fields including sensing [11,12], laser transmission [13,14], communication [15,16], and gas hollow core fiber laser [17,18]. The reduction of modal overlap with silica glass in the cladding leaves a significant decrease of Raman noise from the host material guided in AR-HCF [10].…”

In-situ background-free Raman endoscope using double-cladding anti-resonant hollow-core fibers

“…Compared to other microstructured hollow-core fibers such as Kagome and photonic bandgap hollow core fibers, AR-HCFs offer a much wider low-loss transmission window and a broader tuning range of central wavelength, spanning from the deep ultraviolet to the mid-infrared. As a result, AR-HCFs have found applications in various fields including sensing [11,12], laser transmission [13,14], communication [15,16], and gas hollow core fiber laser [17,18]. The reduction of modal overlap with silica glass in the cladding leaves a significant decrease of Raman noise from the host material guided in AR-HCF [10].…”