| dc.description.abstract | Metamaterials offer a great degree of control over their physical properties through the tuning of the interactions between their elements within larger structures. Molecular Aggregates are a group of organic molecules that assemble into structures with new optical properties arising from the inter-molecule interactions. Molecular aggregates are a fascinating and important class of materials, particularly in the context of optical (pigmented) materials. The aim of this thesis is combine these two fields in the meta-analogue approach by replicating aggregate behaviour with metamaterials. In this way aggregate phenomena normally observed on the nm scale can instead be probed in great detail at the mm scale of a metamaterial. Simultaneously, new metamaterials can be created that are inspired by the study of aggregates. Passive resonant metamaterials are limited by the narrow-band nature of the resonances they support. In order to probe the interaction between two resonators more deeply, and guide experimentation with meta-analgoues, I create a tunable Split Ring Resonator (SRR). I show that by incorporating an active component into the structure of the SRR it is possible to tune the resonance frequency of this type of metamaterial atom. I make use of this tuneability to examine the interaction between two resonators, one passive and one active, as the resonance frequency of the active resonator is swept through that of the passive resonator. The resultant modes of this coupled system exhibit an anti-crossing and, by changing the separation between, and relative orientation of, the split-ring resonators, I investigate how the magnetic and electric coupling terms change. I find that the relative orientation of the resonators significantly effects the strength of the coupling. Through both structural and active tuning we are able to alter the relative sizes and signs of the coupling terms. In the world of researching molecular aggregates it is difficult to precisely examine small numbers of molecules, relying instead on the behaviours of large groups to determine their properties. In the second section I present two meta-analogues of molecular aggregates. A positively dispersive chain of resonators, that couples in a manner analogous to J-aggregates, and a negatively dispersive chain that couples analogously with H-aggregates. I also present two novel metamaterial chains inspired by the aggregate like structures. In the first a simultaneous negative and positive group velocity is achieved and in the second those counter propagating modes are coupled through the breaking of one of the meta-atom's symmetries, resulting in an anti-crossing and a region of zero group velocity. In the third results section, in an effort to achieve greater understanding of these systems of aggregate like chains of meta-molecules on the millimeter scale, I exploited the fact that they can be directly probed and rearranged. Using this system I directly observed the effects of various termination and defect types, in the process showing a clear relation between these and those predicted in the SSH model. I intend for this work to open new avenues of interrogation of aggregate structures using metamaterial analogues as well as of direct observation of localised modes. In the final section I present a meta-analogue of the strong coupling experiment. The formation of polariton modes from the strong coupling of light and matter is an exciting and important field with ramifications from Chemistry to laser physics. It's study is in many ways hampered, however, by the atomic and molecular scale at which interactions take place. In this section I investigate the effects of strong coupling using metamaterial analogues. This allows for the meta-atoms themselves to be directly probed during excitation, and for the nature of hybridised polaritons, and the optically `dark' states to be shown directly. | en_GB |
