Study of a periodic spectral fluctuation existing in a fibered optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS)

Zhifu Luo,Zhongqi Tan,Xingwu Long

doi:10.1186/s41476-019-0120-5

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.

Highlights

There is an urgent requirement for fast, high sensitivity, low detection limit and real-time trace-gas detectors for atmospheric sciences, environmental monitoring, agriculture process control and medical diagnostics nowadays [1, 2]
For the periodic spectral fluctuation appearing in the primary investigation of this optical feedback cavity-enhanced absorption spectroscopy (OF-cavityenhanced absorption spectroscopy (CEAS)) system, its mechanism is analyzed and the mathematical model is proposed, and the experimental results agree well with the theoretical simulation
Some technical proposals are proposed to eliminate this periodic spectral fluctuation, and the experimental results show that this spectral fluctuation can be eliminated efficiently when a prism is optically glued on the backside of the incident mirror

Summary

Introduction

There is an urgent requirement for fast, high sensitivity, low detection limit and real-time trace-gas detectors for atmospheric sciences, environmental monitoring, agriculture process control and medical diagnostics nowadays [1, 2]. When the single-wavelength narrow linewidth semiconductor laser is applied in optical resonant cavity absorption spectroscopy, it seems to be the optimal selection for the detection of small gas molecules which present separated absorption lines. In the application of laser absorption spectroscopy using high finesse optical resonant cavity, representatively, cavityenhanced absorption spectroscopy (CEAS) and cavity ringdown spectroscopy (CRDS) [5], some undesirable phenomenon often occurs in the absorption spectrum, such as the etalon effect and the spectral ripple effect [6].

Results

Conclusion