Light is one of the most marvelous phenomena around us. We use the light that scatters and reflects from our surroundings to orient ourselves, while the energy from the light that is absorbed by organisms fuels most of the life on this planet. The interaction between light and matter depends not only strongly on the atomic and/or molecular properties of the material; as a result of the wave-like nature of light, it also depends on the structure of an object and its surroundings on length-scales in the order of the wavelength. Understanding the precise interaction between light and its environment enables the design of structures with well-defined optical properties. Being able to design when, where and how the light interacts with its surroundings opens up possibilities for many sensing applications.
One of the ways to manipulate light is by scattering of small metallic particles. Exactly how a particle scatters the light depends on how it is shaped, its composition and surrounding. In this doctoral thesis we discuss both experimentally and theoretically how scatterers smaller than the wavelength interact with incident electromagnetic waves, and how this interaction changes when an ensemble of these scatterers is organized into a periodic lattice. Although the frequency range under consideration in this thesis is that of THz frequencies, i.e. far infrared, most of the physics applies to the full electromagnetic spectrum. Especially the range of frequencies in the visible and near-infrared.