Heterodyne photothermal spectroscopy of methane near 1651 nm inside hollow-core fiber using a bismuth-doped fiber amplifier

Abstract

We present laser-based methane detection near 1651 nm inside an antiresonant hollow-core fiber (HCF) using photothermal spectroscopy (PTS). A bismuth-doped fiber amplifier capable of delivering up to more than 160 mW at 1651 nm is used to boost the PTS signal amplitude. The design of the system is described, and the impact of various experimental parameters (such as pump source modulation frequency, modulation amplitude, and optical power) on signal amplitude and signal-to-noise ratio is analyzed. Comparison with similar PTS/HCF-based systems is presented. With 1.3 m long HCF and a fiber amplifier for signal enhancement, this technique is capable of detecting methane at single parts-per-million levels, which makes this robust in-fiber sensing approach promising also for industrial applications such as, e.g., natural gas leak detection.

Amplified Photothermal Phase Modulation for Carbon Dioxide Detection by Operating a Dual-Mode Interferometer at Destructive Interference

“…When the pump power in the input SMF is ∼178 mW, the detected 2f signal of 5% CO 2 in the laboratory conditions is shown in Figure 9a. The absorption lines of 12 CO 2 R(68) and 13 CO 2 R(38) are well-defined without the interference from the absorption of H 2 O. Figure 9b shows the p.p.…”

“…Figure 9b shows the p.p. values of the selected line pair over a period of 1 h, where the blue dots are 12 CO 2 R(68) and the red dots are 13 CO 2 R(38). The average of the 13 CO 2 / 12 CO 2 as 13 R reference is used to calculate the DOB value, as shown by the black dots in Figure 9b.…”

“…Compared with the free-space counterpart, the tightly confined optical mode within the fiber core over a long distance provides an ideal platform for strong light-gas interactions . Gas detection with noise-equivalent concentration (NEC) down to parts-per-billion (ppb) and even parts-per-trillion (ppt) level has been realized for a variety of gas species with different types of photothermal interferometry (PTI). − Detection of nitric oxide down to single-ppb level is realized using heterodyne PTI with 5.26 μm pump and 100-s integration time . By exploiting the noise cancellation property of the mode-phase-difference (MPD) in a dual-mode HCF, acetylene detection down to ppt level was demonstrated with ∼5-m-long HCF .…”

“…qRP f 2 shot (12) q is electron charge. Thus, the total RMS deviation of the output noise can be rewritten as…”

Flow-Enhanced Photothermal Spectroscopy

“…The earliest application of this method for measuring low-concentrated gaseous samples was published in the early 1980s using a Mach–Zehnder interferometer [ 6 ]. To date, many additional PTS instruments have been published, with which a wide variety of gas types have been sensed down to ppb and ppt levels, e.g., nitrogen dioxide [ 7 , 8 ], carbon dioxide [ 9 ] and many others [ 10 , 11 , 12 , 13 ].…”