MHz-rate attenuation-resolved direct absorption spectroscopy for simultaneous temperature and concentration retrieval under non-absorbing interferences

High-speed laser absorption diagnostics in harsh environments are severely challenged by non-absorbing interferences, including additive emission background and multiplicative non-absorbing optical attenuation, such as transmission loss caused by beam steering, window fouling, particle extinction, and collection-efficiency variations. These effects limit the reliability of conventional direct absorption spectroscopy (DAS) for simultaneous temperature and concentration measurements. Here, we propose an attenuation-resolved direct absorption spectroscopy technique, termed α-DAS, for MHz-rate CO sensing under harsh optical conditions. By combining zero-level-background subtraction with mean-subtracted and normalized absorbance analysis, α-DAS separates temperature-sensitive spectral-shape information from concentration scaling and broadband transmission loss. This strategy enables simultaneous retrieval of temperature, concentration, and the non-absorbing transmission coefficient without relying on conventional baseline fitting. The technique was validated in CO/Ar reflected-shock experiments over 860–1943 K, 2.0–4.2 atm, and 2000–8150 ppm, achieving temperature and concentration deviations within approximately ±4% and ±3%, respectively. Its application to acetone pyrolysis further demonstrates time-resolved CO sensing in reacting flows. α-DAS offers a promising route for high-speed absorption diagnostics in harsh environments, with potential extensions to multi-line, multi-species, and broadband-interference-corrected measurements.