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Validation of open-path dual-comb spectroscopy against an O2 background



Nathan Malarich, Brian Washburn, Kevin Cossel, Fabrizio Giorgetta, Griffin Mead, Daniel Herman, Nathan R. Newbury, Ian Coddington


Dual-comb spectroscopy measures greenhouse gas concentrations over kilometer-length open-air paths with high precision. However, characterizing the absolute accuracy of these outdoor measurements is challenging, as most gas species have fluctuating, heterogenous concentrations over these paths. In contrast to greenhouse gases, O2 concentrations are well-known and evenly mixed throughout the atmosphere. We can thus use O2 concentration measurements to evaluate the accuracy of open-path dual-comb spectroscopy. To this end, we construct a dual-comb spectrometer spanning 1240 nm to 1700 nm, which measures O2 absorption features in addition to CO2 and CH4. O2 concentration measurements across a 560 m round-trip outdoor path reach 0.1% precision in 10 minutes. Over seven days of shifting meteorology and spectrometer conditions, 90% of O2 measurements are within 0.4% of the expected global background. This simultaneous O2, CO2, and CH4 spectrometer will be useful for measuring accurate CO2 mole fractions over vertical or many-kilometer open-air paths, where the air density varies.
Optics Express


Malarich, N. , Washburn, B. , Cossel, K. , Giorgetta, F. , Mead, G. , Herman, D. , Newbury, N. and Coddington, I. (2023), Validation of open-path dual-comb spectroscopy against an O2 background, Optics Express, [online],, (Accessed May 29, 2024)


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Created January 30, 2023, Updated March 14, 2023