| Summary: | Abstract A special periodic spectral fluctuation is observed during the study of a fibered high sensitivity optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) for the measurement of trace gas. This spectral fluctuation is different from some phenomenon observed in former OF-CEAS which contain a resonant cavity with V-shaped configuration, such as the etalon effect and the spectral ripple effect. To reveal why this phenomenon happens and how it works, a series of hypothesis are proposed and tested, and the results show that the multi-beam interference of resonance light at the input mirror of the resonant cavity is the main reason for this phenomenon. Based on the multi-beam interference theory, a mathematical modeling of this phenomenon is built, and the theoretical analyses agree well with the experimental results. Some methods to eliminate this phenomenon are proposed and implemented, and the 1σ noise equivalent absorption coefficient of 7.6 × 10− 10 cm− 1 Hz-1/2 is attained with this robust and compact OF-CEAS system.
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