Measurement of Rayleigh scattering cross sections using broadband cavity-enhanced absorption spectroscopy

Correspondence: Jun Duan(jduan@aiofm.ac.cn) , Pinhua Xie (phxie@aiofm.ac.cn)

Broadband cavity-enhanced absorption spectroscopy (BBCEAS) is a highly sensitive in-situ optical gas detection technique. Leveraging multiple light reflections within an optical resonant cavity, this technique yields an effective absorption path length that significantly exceeds the physical length of the cavity. This enables highly sensitive detection of trace gases, even those with extremely weak absorption characteristics. The Rayleigh scattering cross section serves as the metrological foundation for achieving absolute concentration measurements in high-precision spectroscopic techniques. In this work, we attempted to measure the Rayleigh scattering cross sections of various gases in the ultraviolet-visible spectral range. First, the effective absorption path length of the BBCEAS system was precisely calibrated. By measuring the differences in Rayleigh scattering between various gases (such as argon, carbon dioxide, sulfur hexafluoride, etc.) and helium, the Rayleigh scattering cross sections of the target gases were inversely derived, yielding a high-precision experimental dataset of gas Rayleigh scattering cross sections. In addition, considering the variations in Rayleigh scattering cross sections among different gases, a method for identifying unknown gases was proposed. The extinction coefficient of an unknown gas is measured using BBCEAS and compared with databases of known Rayleigh scattering and absorption cross sections to determine its identity, and this study provides a new approach for the rapid optical measurement of gases with negligible absorption features.

Acknowledgements : This research was funded by the National Natural Science Foundation of China (No. 42175155, 42475141), the Anhui Provincial Key R&D Program, China (No. 2023t07020016), the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2023464), and the CASHIPS Director’s Fund (BJPY2024B10).