Laser-induced incandescence (LII), a technique which determines relative soot volume fraction requires calibration for quantitative measurements. Spatially resolved LII signals from soot within methane/air diffusion flames are calibrated using cavity ring-down (CRD) which avoids extrapolation required of less sensitive methods in current use. Possible sources of error due to scattering and polycyclic aromatic hydrocarbon absorption are considered. Comparison of CRD with traditional light extinction and path-integrated LII verifies its accuracy for soot volume fraction (f_v) determination. Using CRD, quantification of LII for parts-per-billion (ppb) f_v levels is demonstrated.
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