Light Scattering by Agglomerates: Coupled Electric and Magnetic Dipole Method.
Light Scattering by Agglomerates: Coupled Electric and
Magnetic Dipole Method.
Mulholland, G. W.; Bohren, C. F.; Fuller, K. A.
Langmuir, Vol. 10, No. 8, 2533-2546, 1994.
Sponsor:National Aeronautics and Space Administration,
light scattering; agglomerates; Rayleigh-Debye light
scattering; sphere sizes
The coupled electric dipole method (CED) for treating
light scattering by an agglomerate particle is extended
to include both the electric and magnetic dipole terms
(CEMD). The accuracy of these two methods along with
the Rayleigh-Debye (RD) method is obtained by comparing
with the exact solution for two spheres in contact. It
is found that the additional term extends the range of
the coupled dipole method from a primary sphere diameter
of about 0.06 mm to about 0.12 mm for soot-like
particles at visible wavelengths. The scattering and
extinction cross sections, the differential scattering,
and the polarization ratio are computed for agglomerates
with 17, 52, and 165 primary spheres for soot-like and
silica-like agglomerates. The agglomerates are
generated by Brownian dynamics computer simulation of
in-flame growth. A comparison is made among RD, CED,
and CEMD. The effects of primary sphere diameter and
agglomerate size on the validity of the RD approximation
is discussed. It is shown that the polarization ratio
computed by CEMD is sensitive to the primary sphere size
independent of agglomerate size.