LIGHT-SCATTERING BY AGGLOMERATES - COUPLED ELECTRIC AND MAGNETIC DIPOLE METHOD

The coupled electric dipole method (CED) for treating light scattering by an agglomerate particle is extended to include both the electric a nd magnetic dipole terms (CEMD). The accuracy of these two methods alo ng with the Rayleigh-Debye (RD) method is obtained by comparing with t he exact solution for two spheres in contact. It is found that additio n of the magnetic dipole term extends the range of the coupled dipole method from a primary sphere diameter of about 0.06 mum to about 0.12 mum for sootlike particles at visible wavelengths. The scattering and extinction cross sections, the differential scattering, and the polari zation ratio are computed for agglomerates with 17,52, and 165 primary spheres for sootlike and silica-like agglomerates. The agglomerates a re generated by Brownian dynamics computer simulation of in-flame grow th. A comparison is made among RD, CED, and CEMD. The effects of prima ry sphere diameter and agglomerate size on the validity of the RD appr oximation are discussed. It is shown that the polarization ratio compu ted by CEMD is sensitive to the primary sphere size independent of agg lomerate size.