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Final Report Summary - NONPLASMETA (Nonlinear Plasmonic Metamaterials)

The researcher work during the 24 months of this Marie Curie project can be classified in six different work lines:

Transformation Optics for Plasmonics
The researcher has been working on the development of a novel theoretical approach to treat plasmonic effects in metal structures presenting geometric singularities. Exploiting transformation optics ideas, he has designed two-dimensional (2D) structures able to collect and concentrate light efficiently over a broad frequency range. Our work has demonstrated that remarkable field enhancements can be achieved in these complex geometries, which increase nonlinear effects (which are proportional to the electric field intensity) when these nanostructures are embedded in a medium having a nonlinear optical response. More recently, he has transferred this methodology from less realistic 2D geometries to threedimensional (3D) ones. Specifically, he has demonstrated that a dimer of touching metal nanospheres also shows the broadband and superfocusing properties reported for their 2D analog. The validity of our transformation optics theoretical framework was comprehensively checked through heavy numerical simulations.

Control of Nanoemitters Radiative Properties through Plasmonics
The development of the transformation optics framework described above required a deep understanding of plasmonic phenomena taking place in metallic nanoparticles. As a result of the researcher’s introduction into this field, a few publications were generated. Firstly, we studied how localized Plasmon resonances can be used to modify the radiation properties of nanoemitters (such as dye molecules or quantum dots) placed in the vicinity of metal nanostructures. In collaboration with other members of my research group, he wrote a review paper on the topic which was published recently. Note that this research line is closely related to nonlinear plasmonics, since gain materials are comprised by a passive medium filled with nanoemitters, which is responsible for the effective active response.

Experimental Verification of Transformation Optics Predictions
In collaboration with other members of my experimental group at Imperial College, the researcher has worked on the design and analysis of experiments devoted to test the validity of his theoretical predictions (described above). Specifically, he has been involved in the realization of two different experiments on plasmonic structures devised using Transformation Optics recipes. One of them used gold single nanoparticles to test the theoretical results in the optical regime, the other used metamaterial semiconductor microstructures to explore the validity of the predictions in the Terahertz range of the electromagnetic spectrum.

Nonlocal Effects in Plasmonic Devices
Using our Transformation Optics formalism, the researcher has explored the impact of nonlocal effects in the optical properties of plasmonic devices. These arise when the spatial extent of the oscillating electromagnetic fields of plasmonic modes is comparable to the Coulomb screening length (which gives the average inter-electronic distance within the metallic nanostructure). We have shown that, although these effects are detrimental for field enhancement purposes, they improve the performance of focusing plasmonic waveguides.

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