Dual-comb spectroscopy for spatially resolved hydrogen combustion diagnostics over a wide temperature range

Dual-comb spectroscopy (DCS) provides exceptional broadband precision for non-intrusive combustion diagnostics. In this work, we present a detailed quantitative reconstruction for laminar hydrogen-air flames across a wide range of thermal conditions, a key regime for advancing clean energy technologies. We employ nonlinear frequency conversion to shift the spectral range of a near-infrared DCS system from the commonly used 1.4 µm region to the optimized 1.34 µm window. This spectral selection significantly reduces environmental interferences and ensures the consistent availability of temperature-sensitive H₂O absorption features across a wide temperature range. To address the inherent spatial non-uniformity in laminar hydrogen flames, we implement a gradient-aware inversion strategy based on a Boltzmann sigmoidal profile. Coupled with a high-temperature H₂O spectral database, this approach allows the parametric reconstruction of spatial profiles of temperature and H₂O mole fraction from single line-of-sight absorption spectra, measured across varying equivalence ratios. The retrieved temperature profiles, within the validated temperature range of the spectroscopic database, show agreement with established reference data within an uncertainty of 50 K. This work establishes a robust DCS framework for hydrogen combustion diagnostics and provides a quantitative reconstruction that will support the development and validation of kinetic models for clean energy applications.