Plasmonic Metasurfaces

Title: Plasmonic Metasurfaces
Authors: Tahir, Asad Ahmad
Date: 2016
Abstract: Nanophotonics is a booming field of research with the promise of chip-scale devices which harness the tremendous potency of light. In this regard, surface plasmons have shown great potential for confining and manipulating light at extreme sub-wavelength scales. Advances in fabrication technology have enabled the scientific community to realize metasurfaces with unconventional properties that push the limits of possible applications of light. This thesis is comprised of computational and experimental studies on plasmonic metasurfaces. The computational study presents efficient design principles for plasmonic half-wave plates using L-shaped nanoantennas. These principles can be used to design waveplates at an operating wavelength of choice and for specific application requirements. The impact of this study goes beyond the efficient design of waveplates: it provides useful insights into the Physics of L-shaped nanoantenna arrays which have been proposed as building blocks for plasmonic metasurfaces. The experimental work investigates the interaction of a plasmonic metasurface, composed of dipole antenna arrays, with an epsilon-near-zero (ENZ) material. This work thus forms a bridge between plasmonics and ENZ materials science, which is a rapidly advancing field in its own right. The first experimental study investigates the exciting unconventional response of plasmonic dipole antennas when placed on a thin indium tin oxide (ITO) film near its ENZ wavelength of 1417 nm. The antenna-on-ITO system has split resonances whose spectral positions are largely independent of the antenna dimensions. The resonance splitting occurs due to coupling between the antenna resonance and the ENZ mode of the ITO film. This coupling results in field intensity enhancements on the order of a 100 in the ITO film. The second experimental study demonstrates, using the z-scan method, that this large field enhancement in the antenna-on-ITO structure further enhances the already strong nonlinearity of ITO around its ENZ wavelength. In particular, the antenna-on-ITO structure exhibits an extremely large nonlinear absorption coefficient, which is two orders of magnitude larger than that of a bare ITO film, and three to five orders of magnitude larger than that of many other nonlinear materials. This thesis thus constitutes a beautiful blend of three thriving areas of research: plasmonics, ENZ materials science and nonlinear optics. The findings reported here have the potential to contribute to all of these fields, and thus have relevance to a broad spectrum of optical scientists.
CollectionThèses, 2011 - // Theses, 2011 -