Simultaneous measurements of absorption at 632 nm and emission at 800 nm and 900 nm along diametric paths are used to infer soot volume fractions based on both absorption and emission and temperatures based on emission in laminar, premixed flat flames. Agreement between soot volume fractions based on emission and absorption is used as an indicator of homogeneity of the optical path. Emission measurements at the gas band-free wavelengths of 2300 nm and 4000 nm for homogeneous paths are used to infer the specific absorption coefficients of soot particles. The results for methane, propane, and ethylene mixed with nitrogen and oxygen show insensitivity of the specific absorption coefficients to fuel type and weak dependence on temperature. An in situ check of optical homogeneity is crucial in obtaining reliable measurements of optical properties.

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