Improving the accuracy and precision of broadband optical cavity measurements

Jun Chen; Donovan P Fullam; Shuaishuai Yu; Olaf Böge; Phuoc Hoa Le; Hartmut Herrmann; Dean S Venables

doi:10.1016/j.saa.2019.04.015

Improving the accuracy and precision of broadband optical cavity measurements

Spectrochim Acta A Mol Biomol Spectrosc. 2019 Jul 5:218:178-183. doi: 10.1016/j.saa.2019.04.015. Epub 2019 Apr 10.

Authors

Jun Chen¹, Donovan P Fullam², Shuaishuai Yu¹, Olaf Böge³, Phuoc Hoa Le³, Hartmut Herrmann³, Dean S Venables⁴

Affiliations

¹ Department of Thermal Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, China.
² School of Chemistry & Environmental Research Institute, University College Cork, Cork, Ireland.
³ Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany.
⁴ School of Chemistry & Environmental Research Institute, University College Cork, Cork, Ireland; Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany. Electronic address: d.venables@ucc.ie.

PMID: 30991294
DOI: 10.1016/j.saa.2019.04.015

Abstract

Most extinction measurements require a stable light source to attain high precision and accuracy. Here, we present a convenient approach to normalize light source intensity in broadband optical cavity measurements. In the absence of sample extinction, we show that the in-band signal - the high finesse spectral region of the optical cavity in which sample extinction is measured with high sensitivity - is strongly correlated with the out-of-band signal. The out-of-band signal is insensitive to sample extinction and can act as a proxy for light source intensity. This normalization approach strongly suppressed in-band intensity changes in two incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instruments with dissimilar light sources and optical cavity properties. Intensity fluctuations in an arc lamp system were suppressed by a factor of 7 to 16 and in the LED spectrometer by a factor of 10. This approach therefore improves the accuracy and precision of extinction measurements where either property is limited by the light source stability.

Keywords: Aerosol; Atmospheric; Broadband optical cavity; Gases; Normalization; UV/visible.