Light-matter interaction mediated by localised and propagating surface plasmons

Understanding how light-matter interactions can be enhanced is the central theme of much of solid state physics research currently. The potential applications of being able to harness and control light at the nano scale would bring about a new generation of devices the likes of which have not been seen since the infancy of silicon based electronics. Such applications touch all the sciences, from information processing in optical quantum computing to magnetic data storage, single molecule sensing, more efficient solar cells and even highly localised cancer therapy. Surface plasmons are one of the most promising approaches to this end. At their most fundamental level they are electromagnetic waves - light - coupled to conduction electrons of a metallic material that can both propagate and locally resonate in structures much smaller than the wavelength of visible light. These properties, when combined with careful design and material choice, lead to nano structures that are capable of creating regions with fields many orders of magnitudes more intense than free space in volumes smaller than the diffraction limit. Antennas with gaps on the scale of nanometers are able to produce such an environment via plasmons, with much stronger fields than any other structure. When combined with waveguides, structures designed to transport light as efficiently as possible, then a myriad of different devices can be created. This thesis examines a specific set of plasmonic structures, namely bar antennas, gap plasmon waveguides and dimer antennas. In particular, it examines the coupling of light from a focussed beam to a nanogap plasmonic waveguide via a dimer antenna coupling approach. It will be shown how these were analysed from a phenomenological approach by modelling their response with classical coupled oscillators, measuring their spectral behaviour via their extinction cross sections and their design optimised for maximum incoupling of free space radiation in the the waveguide in the visible regime. The most efficient design was identified and its response experimentally measured, where the free space coupling efficiency was found to be 28%, in agreement with theoretical simulations. Computer vision algorithms were employed to automate the image processing of hundreds of experimental measurements. A characterisation tool to map the near fields of such devices is also introduced, cathodoluminescence, whose resolution is only limited by the focal spot of an electron beam. A new way way of imaging using this tool maps the reciprocal space of the local density of optical states and can be acquired in a single shot in only a few seconds.Open Acces

Superior to one of Glass: Natural Gradient index Lenses via Patchy Particle Self-Assembly

To achieve acute and sensitive vision in a camera-like eye in the ocean, a graded refractive index spherical lens is required to maximize the photon flux on the retina, while leaving an eye structure that fits in the head of an animal. This biological lens must also maintain low protein density fluctuation at the length-scale of a wavelength of visible light in order to maintain transparency. In squids, this sophisticated optical design emerges from the properties of a single protein fold, the S-crystallin. In this thesis, I study the material properties and the self-assembly of the squid lens system. I show that squids have evolved graded index and low density fluctuation in a spherical lens using a suite of proteins that can act as patchy colloids with specific, low valence (M=2 or M=3) with geometric flexibility in bond angles. We conducted small x-ray scattering (SAXS) at different radial positions of the lens, and performed a Monte Carlo simulation to estimate structures consistent with the SAXS result. This analysis suggests that lens proteins may form a gel with gradient density throughout the cellular lens structure, with density mediated by a tightly controlled protein coordination number in each region of the organ. Patchy colloid theory may therefore explain both the graded refractive index lens and the transparency evolved in the lens. I also studied the Chinese century egg, which appears to be a physically analogous system of a protein-based, low-valence patchy colloidal gel that was developed in prehistoric Chinese culinary culture as a method of egg preservation. I compare the structure and material properties of these two systems

Searching Data Cube for Submerging and Emerging Cuboids

International audience—Many existing approaches to data cube computation search for the group-by partitions on fact table with support greater than some threshold, that is, those can be obtained from the SQL group-by queries with the clause HAVING COUNT(*) >= supp, where supp is a support threshold. Those partitions constitute what is called the iceberg data cube. The present work proposes an efficient method to compute the similar partitions, but in contrast to those previous approaches, in the clause HAVING, COUNT(*) can be >= supp or < supp. Generally, the method can search for the partitions that can be in the emerging part or in the submerging part of data cube, and on any other aggregate functions, not only the function COUNT

Full Proceedings, 2018

Full conference proceedings for the 2018 International Building Physics Association Conference hosted at Syracuse University