National Research Council of Canada. Measurement Science and Standards
33th International Combustion Symposium, August 1-6, 2010, Beijing, China
A cornerstone of the theory of laser induced incandescence applied to soot aerosols is that the soot is not affected by rapid laser heating. However, it has been demonstrated in the literature that intense laser irradiance typical of ‘high’ or ‘plateau regime’ LII leads to significant modification of the internal structure of soot particles [Vander Wal] and even the formation of new particles from vaporized material [Michelsen]. For moderate laser fluences typical of auto-compensating LII (AC-LII) [Snelling], morphological changes are not observable via high resolution transmission electron microscopy (HR-TEM) [Michelsen]; however, it is still conceivable that the rapid heating of soot aggregates to temperatures in the range of 3000 to 4000 K can influence the internal crystalline structure of soot as well as materials adsorbed on the surface and thus the optical properties of the soot may change as a consequence of the laser heating. Variation of the optical properties of the soot on time scales relevant to LII measurement would have impacts on the interpretation of signal which must be accounted for.