Applications Of The DDA Method In Light Scattering By Particles

The discrete dipole approximation (DDA) is a flexible and powerful technique for studying the scattering and absorption characteristics of targets with arbitrary geometry. In this thesis, the scattering properties of the sphere and spheroid particle are analyzed. And the scattering properties of some typical aggregates are studied as well. The structure of the carbon aggregate particles is simulated with the fractal theory and the problem of the electromagnetic absorption by the soot aggregates is discussed.Firstly, the basic theory and the equations of the discrete dipole approximation are derived. Then the Lorenz Mie theory and the DDA theory are applied to calculate the scattering properties of the sphere and spheroid particle illuminated by the plane wave or Gaussian beam wave. Results of these two methods agree well, which indicates that the DDA theory is of great accuracy. Then the DDA theory is used to study some typical aggregates which are composed by small spherical particles, and the results are compared with the Generalized Multiparticle Mie-solution (GMM) and the experimental data in the referenced literatures. It can be seen that the DDA theory is quite suitable for calculating the scattering properties of aggregate particles. At last, the structure of the soot aggregates is modeled by the fractal theory. Taking account of the size distribution and the refractive indices of the carbon aggregate particles, the electromagnetic absorption by the soot aggregates is analyzed with the DDA theory.