Development of plasmonic metamaterials for the control of optical absorption, thermal radiation and light propagation

The desire to go beyond the reflection and refraction of conventional materials has led to great interest in engineered plasmonic metamaterials. Restricted by the range of permittivity and permeability of natural materials, conventional photonic devices are limited in their abilities to manipulate light. Metamaterials are artificially engineered structures with subwavelength features whose optical properties transcend those found in nature. Due to their unique electromagnetic response, metamaterials have generated many new and exciting applications such as perfect lenses, hyperlenses, invisibility cloaking, light trapping, and beam steering, etc. We have studied several topics in this field including basic metamaterial building blocks, simulation models, and potential applications. First, we experimentally investigate the absorption properties of one specific metamaterial (i.e. hyperbolic metamaterials), which support propagating waves with anomalously large wavevectors and high photonic-density-of-states over a broad bandwidth. Second, we develop a theoretical description of radiative thermal conductivity in hyperbolic metamaterials. We demonstrate a dramatic enhancement of the radiative thermal transport due to the super-singularity of the photonic density of states in hyperbolic media, leading to the radiative heat conductivity which can be comparable to the non-radiative contribution. Third, for the application in thermo-photovoltaics, we demonstrate an ultra-thin refractory plasmonic thermal emitter operating at high temperatures (560 °C). The spectrally selective emitter exhibits high emissivity at around 2.5 µm and below, and suppresses emission at longer wavelengths. Fourth, we show experimentally that the thermal excitation of surface plasmon polariton on the surface of titanium nitride (TiN) grating operating at high temperature (540 °C) allows us to get a quasi-coherent beam at 3 µm. This coherence can be used to design quasi-monochromatic and highly directional thermal sources. Fifth, as for the efficient modelling of metasurfaces for beam steering, we report a numerical study of a new bianisotropic parameter retrieval technique for antenna metasurface. Frequency Domain Finite Difference solver is developed to integrate the bianisotropic descriptions of each antenna and describe a fully functional metasurface