Studies of metamaterial structures

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The impact of natural modes in plasmonic imaging

Plasmonic imaging is crucial for understanding cellular behaviours for biological sciences, where is used to image and track organelles in cells, such as DNA and virus molecules. Due to the fast dynamics of the intra-cellular processes, it is essential to keep the cells under their native states (i.e. label-free), establishing plasmonic imaging as one of the most powerful tools for studying biological samples. In this article, a theoretical model is presented that accurately predicts the properties of a plasmonic image, paving the route towards the characterization of an imaged nano-object. It is shown that natural modes are not only excited, but actually dominate the intensity and shape of the observed plasmonic image. Hence, the proposed model explains the dynamics forming the plasmonic image and can be used to extract spectroscopy information from current plasmonic imaging techniques

Analytic theory of optical nanoplasmonic metamaterials

Recent advances in nano-fabrication techniques allow for the manufacture of optical metamaterials, bringing their unique and extra-ordinary properties to the visible regime and beyond. However, an analytical description of optical nano-plasmonic metamaterials is challenging due to the characteristic optical behaviour of metals. Here we present an analytical theory that allows to bring established microwave metamaterials models to optical wavelengths. This method is implemented for nano-scaled plasmonic wire-mesh and tri-helical metamaterials, and we obtain an accurate prediction for their dispersive behaviour at optical and near-IR wavelengths

Optical nano-woodpiles: large-area metallic photonic crystals and metamaterials.

Metallic woodpile photonic crystals and metamaterials operating across the visible spectrum are extremely difficult to construct over large areas, because of the intricate three-dimensional nanostructures and sub-50 nm features demanded. Previous routes use electron-beam lithography or direct laser writing but widespread application is restricted by their expense and low throughput. Scalable approaches including soft lithography, colloidal self-assembly, and interference holography, produce structures limited in feature size, material durability, or geometry. By multiply stacking gold nanowire flexible gratings, we demonstrate a scalable high-fidelity approach for fabricating flexible metallic woodpile photonic crystals, with features down to 10 nm produced in bulk and at low cost. Control of stacking sequence, asymmetry, and orientation elicits great control, with visible-wavelength band-gap reflections exceeding 60%, and with strong induced chirality. Such flexible and stretchable architectures can produce metamaterials with refractive index near zero, and are easily tuned across the IR and visible ranges.We acknowledge financial support from EPSRC grant EP/G060649/1, EP/I012060/1, EP/L027151/1, ERC grants LINASS 320503 and 3DIMAGE 291522, EU FP7 280478, and the Leverhulme Trust and Rolls-Royce plc.This is the final version of the article, originally published in Scientific Reports 5, Article number: 8313. DOI: 10.1038/srep08313

Ultrafast nonlinear response of gold gyroid three-dimensional metamaterials

We explore the nonlinear optical response of 3D gyroidal metamaterials, which show >10-fold enhancements compared to all other metallic nanomaterials as well as bulk gold. A simple analytical model for this metamaterial response shows how the reflectivity spectrum scales with the metal fill fraction and the refractive index of the material that the metallic nanostructure is embedded in. The ultrafast response arising from the interconnected 3D nanostructure can be separated into electronic and lattice contributions with strong spectral dependences on the dielectric filling of the gyroids, which invert the sign of the nonlinear transient reflectivity changes. These metamaterials thus provide a wide variety of tuneable nonlinear optical properties, which can be utilised for frequency mixing, optical switching, phase modulators, novel emitters, and enhanced sensing.This is the author's accepted manuscript. The final version is available from APS in Physical Review Applied at http://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.2.044002#fulltext#fulltext

Anomalous Spectral Shift of Near- and Far-Field Plasmonic Resonances in Nanogaps.

The near-field and far-field spectral response of plasmonic systems are often assumed to be identical, due to the lack of methods that can directly compare and correlate both responses under similar environmental conditions. We develop a widely tunable optical technique to probe the near-field resonances within individual plasmonic nanostructures that can be directly compared to the corresponding far-field response. In tightly coupled nanoparticle-on-mirror constructs with nanometer-sized gaps we find >40 meV blue-shifts of the near-field compared to the dark-field scattering peak, which agrees with full electromagnetic simulations. Using a transformation optics approach, we show such shifts arise from the different spectral interference between different gap modes in the near- and far-field. The control and tuning of near-field and far-field responses demonstrated here is of paramount importance in the design of optical nanostructures for field-enhanced spectroscopy, as well as to control near-field activity monitored through the far-field of nano-optical devices.We acknowledge financial support from EPSRC grants EP/G060649/1, EP/L027151/1, EP/G037221/1, EPSRC NanoDTC, and ERC grant LINASS 320503. J.A. acknowledges support from project FIS2013-41184-P from Spanish MINECO and project NANOGUNE'14 from the Dept. of Industry of the Basque Country. F.B. acknowledges support from the Winton Programme for the Physics of Sustainability. R.C. acknowledges financial support from St. John's College, Cambridge for Dr. Manmohan Singh Scholarship. P.A. acknowledges funding from the Helmholtz Association for the Young Investigator group VH-NG-928 within the Initiative and Networking fund. We thank Laurynas Pukenas and Steve Evans (University of Leeds, UK) for support with the ellipsometry measurementsThis is the final version of the article. It first appeared from the American Chemical Society via https://doi.org/10.1021/acsphotonics.5b0070

Exact Quantum Electrodynamics in Radiative Photonic Environments

We present a comprehensive second quantization scheme for radiative photonic devices. We canonically quantize the continuum of photonic eigenmodes by transforming them into a discrete set of pseudomodes that provide a \textit{complete} and \textit{exact} description of quantum emitters interacting with electromagnetic environments. This method avoids all reservoir approximations, and offers new insights into quantum correlations, accurately capturing all non-Markovian dynamics. This method overcomes challenges in quantizing non-Hermitian systems and is applicable to diverse nanophotonic geometries