Depolarized light scattering from fractal soot aggregates

We have measured the depolarization ratio {ρ} of light scattered from three different premixed hydrocarbon-oxygen flames. The soot clusters in these flames are well described as fractals with a dimension of 1.79±{}0.10. We show that the depolarization is due to intracluster multiple scattering. We also show that {ρ}{~}N^-0.6, where N is the number of monomers per cluster for scattering in the forward direction. We created simulated diffusion-limited-cluster-aggregate clusters on a computer and used a self-consistent electric-dipole-induced-dipole calculation to calculate {ρ} and again find {ρ}{~}N^-0.6. The calculated magnitude, however, is too small; various modifications are tried or suggested to bring about a quantitative agreement of theory and experiment.