Comparisons of the discrete-dipole approximation and modified double interaction model methods to predict light scattering from small features on surfaces

Two numerical methods to model light scattering from illuminated features o n surfaces are presented. The discrete-dipole approximation (DDA) method is considered, as well as the modified double interaction method (MDIM). The DDA method models electromagnetic scattering of continuous features using d iscrete dipoles placed on a lattice structure. Sommerfeld integral terms ar e used to model dipole/surface interaction in the near-field. The MDIM meth od first computes scattering from the features based in free space using ot her methods such as Mie theory or other standard light scattering codes (in cluding DDA). The surface interaction is modeled as a first approximation b y means of a geometrical shadowing effect and the Fresnel coefficients. Com parisons of the methods will be shown for light scattering from spherical f eatures. The material properties of dielectric and metallic materials will be considered and the feature sizes will be varied. The prediction accuracy and computational requirements of each method will be investigated. For mo st cases, the studies will show that the DDA method is more accurate than t he MDIM method for dielectric materials since the modeling of the feature a nd surface electromagnetic interaction is more accurate; however, the modif ied double interaction method may be advantageous over the discrete-dipole approximation method for metallic features because of lesser computational times and memory requirements. (C) 2001 Elsevier Science Ltd. All rights re served.