- Author
- Mulholland, G. W. | Bohren, C. F. | Fuller, K. A.
- Title
- Light Scattering by Agglomerates: Coupled Electric and Magnetic Dipole Method.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD Pennsylvania State Univ., University Park Colorado State Univ., Fort Collins
- Journal
- Langmuir, Vol. 10, No. 8, 2533-2546, 1994
- Sponsor
- National Science Foundation, Washington, DC National Park Service, Washington, DC National Aeronautics and Space Administration, Washington, DC
- Contract
- NSF-GRANT-ATM-8810876 NA90RAH000077 NASA-GRANT-W-17980
- Keywords
- light scattering | agglomerates | Rayleigh-Debye light scattering | sphere sizes
- Identifiers
- coupled electric dipole (CED) method; fractal dimension; polarization ratio; radius of gyration; smoke agglomerate
- Abstract
- 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 µm to about 0.12 µm 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.