Electromagnetic scattering by an isolated particle or a multi-particle group is a ubiquitous phenomenon central to a wide variety of science and engineering disciplines. Field—matter interactions described by macroscopic electromagnetics typically occur in a natural way. They can affect accompanying physical and chemical processes as well as the very state of the scattering object and often yield an electromagnetic signal that can be measured and analyzed with the purpose of retrieving useful information about the object. Electromagnetic scattering can also be induced artificially and used as an active means of in situ or remote diagnostics of certain physical properties of the particle(s). In order to interpret laboratory, field, and remote-sensing measurements of electromagnetic scattering by various single- and multi-particle objects, one needs a deep understanding of this phenomenon, as well as the ability to predict quantitatively its various manifestations as functions of the physical parameters of the objects.

The diversity of sizes, morphologies, and refractive indices of particles encountered in natural and artificial environments is virtually limitless, as illustrated by Fig. 1.1. This factor complicates accurate quantitative modeling of electromagnetic scattering and absorption, even by solitary particles such as those suspended individually in the trap volume of an electrostatic (as shown in Plate 1.1a) or optical levitator. The task of optical modeling of a large group of sparsely distributed particles such as a cloud (see, e.g., Plates 1.1b and 1.1c) is significantly more involved.