ABSTRACT

Plasmonic antennas as an analogue at the nanoscale are of great interest due to the unique ability of metallic nanostructures to manipulate the absorption and emission at optical frequency. The efficiency of a plasmonic antenna depends on its shape, material, dimension, assembly, and operation frequency. This chapter introduces single nanoantennas of various shapes and their far-and near-field properties. Nanoantennas of different geometries that can effectively control various light properties such as the intensity, direction, and polarization of emission are discussed. Not only the tunable far-field radiation but also a huge local field enhancement can be obtained in the vicinity of plasmonic antennas under resonant excitation. The coupled plasmonic metallic nanostructures can concentrate light in well-defined electromagnetic hot spots, which is a common way to enhance the performance of nanoantennas. In the Yagi-Uda gold nanoantenna, elements are well separated from each other, which is relatively large for plasmonic coupling.