A New Method to Calculate the Extinction Properties of Irregularly Shaped Particles

A new method to calculate the extinction of light by irregularly shaped particles, the generalized semianalytical (GSA) method, is described. It allows a better approximation of the shape of a particle by interpolating explicitly the polarization field sampled at various points within the particle. The performance of the GSA method is compared to that of the discrete dipole approximation (DDA) method and of two other methods which solve for the surface polarization field in the zero-frequency limit: the Fuchs method, and the semianalytical (SA) method. The GSA method yields an improved accuracy compared to the other methods for moderate optical constants and shows less variability as a function of grid resolution than the DDA method. It is also found that the DDA method tends to systematically overestimate the extinction, especially when the incident wave polarization vector is perpendicular to the major axis of elongated structures. In addition, for finite size parameters, the GSA method and DDA method are compared to Mie spheres and spheroids. Again, the DDA method is shown to overestimate the extinction systematically, whereas the GSA method yields better accuracy for small size parameters. The likely sources of this discrepancy are discussed.