Analysis of the optical characteristic of particles by the discrete dipole approximation method

Abstract

The method for measuring particles size and concentration based on the light extinction is widely used in the particles measurement technology. In the light extinction method, the extinction efficiency factor is an important parameter. Using the Mie theory, the extinction efficiency factor of spherical particles and equivalent-volume spheres instead of nonspherical particles can be calculated. For analyzing the characteristics of the non-spherical particles, the discrete dipole approximation (DDA) method is presented in this paper. The extinction efficiency factors of spherical, ellipsoid and cylinder particles were calculated by using the DDA method under different size parameters, and compared with the results of the equivalent-volume spheres based on Mie theory. The calculation results show that the extinction efficiency factors of spherical particles obtained by two methods differ slightly under the whole size parameters. The extinction efficiency factor of non-spherical particles and equivalent-volume spheres have discrepancy in evidence. The discrepancy between them changes with the different parameters of shape and size. Furthermore, it should be noted that when the size parameter is less than a critical size parameter, the extinction efficiency factor of non-spherical particles obtained by two methods differ slightly, and when the size parameter is greater than a critical size parameter, the extinction efficiency factor of non-spherical particles obtained by two methods differ greatly along with the increase of the size parameter, the non-spherical effect on the extinction efficiency factor can not be ignored. By contrast with the Mie theory, the DDA method has greater potential in application.