Optical properties of pulsed laser heated soot
- 217 Downloads
To investigate the transient change of soot optical properties resulting from pulsed laser heating of soot in a cooled exhaust plume we have simultaneously performed cw light extinction at 405 and 830 nm and elastic light scattering at 1064 nm. A reversible increase to the 830-nm light extinction of up to 7%, observed during the time period where the soot was hot, suggests a temperature-dependent light absorption refractive index function, E(m λ ). At low fluence, small permanent increases of E(m λ ) of <2% were also observed. 405-nm extinction measurements revealed that the soot likely contained material which continued to absorb 405-nm radiation when desorbed, thus complicating measurement interpretation. 1064-nm light scattering measurements showed a gradual decrease of scattering propensity with increasing laser fluence up to the point of material loss, which is consistent with the expected decrease of the structure factor of the soot aggregates as they expand. It is concluded that variations of the optical properties are occurring at the time of laser-induced incandescence (LII) emission, which should be accounted for in time-resolved LII measurement interpretation.
KeywordsSoot Particle Laser Heating Light Extinction Extinction Measurement Soot Temperature
Unable to display preview. Download preview PDF.
- 5.F. Liu, D.R. Snelling, in 40th AIAA Thermophysics Conf. (2008), paper 2008–4362 Google Scholar
- 13.C.F. Bohren, D.R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983) Google Scholar
- 14.C.M. Sorensen, Aerosol Sci. Technol. 35, 648 (2001) Google Scholar
- 20.D.R. Snelling, O. Link, K.A. Thomson, G.J. Smallwood, Appl. Phys. B, Lasers Opt. (2011). doi: 10.1007/s00340-011-4394-6
- 28.A.R. Coderre, K.A. Thomson, D.R. Snelling, M.R. Johnson, Appl. Phys. B, Lasers Opt. (2011). doi: 10.1007/s00340-011-4448-9
- 33.H.-H. Grotheer, K. Wolf, K. Hoffmann, Appl. Phys. B, Lasers Opt. (2010), submitted Google Scholar