Abstract
A trace acetylene (C2H2) detection system was demonstrated using the cavity-enhanced absorption spectroscopy (CEAS) technique and a near-infrared distributed feedback (NIR-DFB) laser. A Fabry–Perot (F–P) cavity with an effective optical path length of 49.7 m was sealed and employed as a gas absorption cell. Co-axis cavity alignment geometry was adopted to acquire a larger transmitted light intensity and a higher sensitivity compared with off-axis geometry. The laser frequency was locked to the cavity fundamental mode (TEM00 mode) by using the Pound–Drever–Hall (PDH) technique continuously. By introducing a cavity length-locking loop, the drift of the cavity length was suppressed, and the stability of the system was enhanced. To demonstrate the efficacy of the system, a C2H2 absorption spectrum near 6534.36 cm−1 was acquired by tuning the laser operation temperature. Measurements of C2H2 samples with different concentrations were carried out, and a good linear relationship between C2H2 concentration and the cavity-transmitted signal voltage was observed. The measurement results showed the system could work stably for more than 2 h without major fluctuations. The Allan variance analysis results demonstrated a detection limit of 9 parts-per-billion (ppb) with an averaging time of 11 s corresponding to a minimum detectable absorption coefficient of 1.1 × 10−8 cm−1.
Highlights
Acetylene (C2 H2 ) plays an important role in illumination, metal welding, and industrial production
C2 H2 is a kind of indicating gas dissolved in transformer oil
Among commonly used detection techniques for trace C2 H2, resonant cavity-based infrared laser absorption spectroscopy techniques have attracted a lot of interest with the advantages of high detection sensitivity, fast response, and small sample volume
Summary
Acetylene (C2 H2 ) plays an important role in illumination, metal welding, and industrial production. C2 H2 is a kind of indicating gas dissolved in transformer oil. The monitoring of C2 H2 concentration is of great significance for working state and performance evaluation of the transformer [4,5]. Among commonly used detection techniques for trace C2 H2 , resonant cavity-based infrared laser absorption spectroscopy techniques have attracted a lot of interest with the advantages of high detection sensitivity, fast response, and small sample volume Techniques such as cavity ringdown spectroscopy (CRDS) [6,7,8] and cavity-enhanced absorption spectroscopy (CEAS) [9,10] make use of high-finesse optical cavities that greatly increase the effective optical path length, thereby improving the detection sensitivity
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