An investigation of dependent independent scattering regimes using a discrete dipole approximation

Dependent scattering/independent scattering regimes are investigated in two different particle systems using a discrete dipole approximation for modeling the interaction of electromagnetic waves with the matter. In the first case, absorption and scattering by two small Rayleigh spheres, separated at an arbitrary distance, are discussed and compared against the Lorenz-Mie theory predictions for single spheres. After that, small agglomerates of up to 12 spheres are investigated. Results show that the mutual interaction of two spheres does not affect absorption when the ratio of their distance to the radius, c = d/a, is greater than 3. Contrary, an analogous criterion for independent scattering depends on the individual sphere size parameter, x(s), such that it is valid only if c greater than or equal to 2/x(s). It is shown that an agglomerate formed of N individual spheres can be approximated by an effective sphere if x(e) less than or equal to 0.2. For x(e) approximate to 2, agglomerates scatter similar to N independent particles. These limits bracket the true radiative properties of the agglomerates for 0.2 less than or equal to x(e) less than or equal to 2; where dependent effects cannot be neglected. Additionally, an experimental methodology is suggested to qualitatively identify the process of agglomeration of a number of individual particles even when changes in the number density of particles are unknown.