| dc.description.abstract | The random thermal motion of charges in a material results in emitted radiation that is spatially and temporally incoherent. The spatial incoherence corresponds to the lack of correlation between the oscillating dipoles responsible for the thermal field, while the temporal incoherence corresponds to the broadband nature of the emitted radiation. By making use of surface waves that have characteristic resonant frequencies and can propagate along an interface, it is possible to achieve some form of both spatial and temporal coherence. In particular, in materials that support collective charge oscillations, either of free electrons or in the form of lattice vibrations, light can couple to the material charges, resulting in quasiparticles that take on an intermediary character between the light and the material charge. This allows the long wavelengths of the infrared to approach the much smaller length scales associated with the charge oscillations, potentially permitting the design of small form factor devices for the infrared with tailored coherence properties. This thesis explores the ways in which polaritonic excitations can be used to direct and manipulate electromagnetic energy. For those materials where light couples to lattice vibrations, the symmetry of the crystal will dictate how the coupled light can travel. Since many natural crystals have inherent structural anisotropy, light can potentially propagate at different speeds in different crystallographic directions. Understanding the role of reduced symmetry for the propagation of surface polaritons has implications for the design of novel thermal emission and heat transfer devices, where thermal energy can be transmitted in controlled directions at unprecedented speeds. | |
