A Light Scattering Model for Large Particles with Surface Roughness

A physical-optics hybrid method designed for the computation of single-scattering properties of particles with complex shapes, including surface roughness, is presented. The method applies geometric optics using a novel ray backtracing algorithm to compute the scattered field on the particle surface. A surface integral equation based on the equivalence theorem is used to compute the scattered far-field, which yields the full Mueller matrix and integrated single-scattering parameters. The accuracy is tested against the discrete dipole approximation for fixed orientation smooth and roughened compact hexagonal columns for 3 values of refractive index. The method is found to compute asymmetry parameter, and scattering and extinction efficiencies with mean errors of −1.0%, −1.4%, −1.2%, respectively, in a computation time reduced by 3 orders of magnitude. The work represents a key step forwards for modelling particles with physical surface roughness within the framework of physical-optics and provides a versatile tool for the fast and quantitative study of light scattering from non-spherical particles with size much larger than the wavelength.