Recent developments in nanotechnology have made it possible to create a large variety of nanoparticles with predefined shapes. Nanoparticles that are much smaller than the optical wavelengths can appear as artificial atoms to light and, when assembled into a periodic three dimensional lattice, they form a crystalline optical nanomaterial. The main difference from natural materials is that the optical response of the material can be purposefully tailored by designing the constituting nanoparticles. In fact, optical nanomaterials can exhibit extraordinary optical properties that cannot be found in natural materials. However, in order to successfully design such artificial media, advanced theoretical methods are required. The main goal of the research described in this thesis was to develop a theoretical basis for a comprehensive treatment of optical nanomaterials. In the developed formalism, the microscopic optical response in the unit cell of a nanomaterial is characterized in terms of elementary electric current multipoles. These multipoles are fundamentally connected to the nanoparticles' geometry, which provides an efficient way to adjust and tune the optical response. The influence of higher-order multipole excitations is demonstrated by designing a nanoscatterer in which light cannot excite any electric dipole moment. In the thesis, it is shown that the macroscopic optical properties of nanomaterials can straightforwardly be described in terms of the interaction of optical plane waves with the planar arrays of nanoscatterers that compose the medium. Effective material parameters, such as the refractive index and wave impedance, naturally appear in this description in the form of simple analytical expressions. In contrast to existing theories, the introduced approach correctly handles also spatially dispersive materials, including those composed of noncentrosymmetric nanoscatterers. In such materials, two counterpropagating waves can experience the medium differently. The developed theory reveals the fundamental role of higher order multipoles and spatial dispersion in realizing extraordinary optical properties with designed nanomaterials. In particular, materials composed of asymmetric nanoparticles may find novel light-guiding and light-harvesting applications. Furthermore, nanomaterials can be designed to suppress optical reflection at certain interfaces only, which can be exploited, e.g., in new interferometric optical devices. Most of the introduced theory can be straightforwardly applied to other artificial media, such as radiofrequency metamaterials and, in some cases, photonic and phononic crystals.
|Translated title of the contribution||Theoretical Description and Design of Optical Nanomaterials|
|Publication status||Published - 2014|
|MoE publication type||G5 Doctoral dissertation (article)|
- optical metamaterials
- electromagnetic material parameters
- electromagnetic multipoles
- spatial dispersion