Currently laser-induced incandescence (LII) is widely used for the measurement of soot volume fraction. A particularly important aspect of the technique that has received less attention, however, is calibration. The applicability of cavity ringdown (CRD) for measurement of soot volume fraction <i>f</i><sub><i>v</i></sub> is assessed, and the calibration of LII by means of CRD is demonstrated. The accuracy of CRD for <i>f</i><sub><i>v</i></sub> determination is validated by comparison with traditional light extinction and path-integrated LII. By use of CRD, the quantification of LII for parts in 10<sup>9</sup> (ppb) <i>f</i><sub><i>v</i></sub> levels is demonstrated. Results are presented that demonstrate the accuracy of CRD for a single laser pulse to be better than ∓5% for measurement of ppb soot volume-fraction levels over a 1-cm path length. By use of CRD, spatially resolved LII signals from soot within methane–air diffusion flames are calibrated for ppb <i>f</i><sub><i>v</i></sub> levels, thereby avoiding the extrapolation required of less sensitive methods in current use.
© 1999 Optical Society of America
Randy L. Vander Wal and Thomas M. Ticich, "Cavity Ringdown and Laser-Induced Incandescence Measurements of Soot," Appl. Opt. 38, 1444-1451 (1999)