Manipulating light-matter interactions with plasmonic metamolecules and metasurfaces : a route to control absorption and scattering at the nanoscale

The interaction of electromagnetic waves with materials is at the basis of several phenomena influencing our everyday lives. Throughout the past few decades we are witnessing a rapid progress in the development of new platforms to engineer and design different aspects of wave-matter interaction for applications ranging from green energy harvesting, to high speed data communication, and medicine. In line with these developments, the advent of metamaterials, or artificially structured materials, introduces an alternative path to mold and control electromagnetic waves with degrees of freedom that are not accessible in natural materials. There is, however, a strong need to broaden the range of applicability of metamaterials thorough strong nanoscale light management, real-time tunability, ease of fabrication, and lowering the losses. In this study we discuss that to what extent it is possible to engineer the scattering, absorption, and local wave-matter interaction of metamolecules, as the basic building-blocks of metamaterials, as well as assembles of them forming complex systems. In this work, first, we propose and investigate new nanoparticle geometries with tailored complex absorption and scattering signatures. We demonstrate that plasmonic-based nanostructures can be tailored to provide unprecedented control of their scattering and absorption/emission response over broad bandwidths, specifically in the optical frequency range. We show that judicious combination of plasmonic-dielectric singular nanoparticles provides very efficient broadband and controllable light absorption and amplification. Based on these composite elements, we propose a nanoscale optical switch with strong sensitivity and tunability. These engineered nanoparticles are also particularly interesting for applications in nonlinear optics, spasing, and energy-harvesting devices. Next, we answer the fundamental question of "to what extent the unwanted scattering from a general absorbing body may be reduced?". We demonstrate the theoretical limitations of a furtive sensor and provide a proof of the concept implementation of minimum-scattering superabsorbers at optical and microwave frequencies. Based on our theoretical analysis, we also explore experimental realization of microwave low-scattering antennas. This study is of particular importance for the near-field subdiffractive probing and closely-packed antenna designs. Last, we propose a new degree of freedom in controlling the propagation and scattering of light through proper arrangements of dissimilar metamolecules over a surface, i.e. gradient metasurfaces. We theoretically investigate and design metasurfaces that are capable of performing complex wave shaping functionalities such as cloaking, yet, over a single ultrathin volume. Our full analytical approach enables us to underline the inherent limitations and wide range of capabilities of metasurfaces, and we propose novel techniques to significantly improve the efficiency of wave manipulation by metasurfaces. We also investigate the proposed concept of local wave manipulation in several practical applications in beam steering, improved energy harvesting, and cloaking arbitrary obstacles, accompanied by experimental realization of negative reflection from optical metasurfaces. Such unprecedented control of optical wave propagation along with compatibility of metasurfaces with standard lithographic techniques and on-chip technology will significantly impact the future application of metasurfaces, paving the way toward flat, compact optical devices.