11 research outputs found

    Design for optical metamaterial design for optical metamaterial absorber

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    ÔÇťOptical metamaterlal (MM) absorbers in the visible or near-infrared range have been widely investigated in these years since they are crucial in many promising applications, such as solar energy harvesting systems, thermo-photovoltaic energy conversion devices, thermal imaging and emissivity control. This dissertation aims to design and investigate various optical metamaterial absorbers based on different mechanisms and theories, such as cavity resonance, impedance match, equivalent circuit model and waveguide stop light mode. First, via utilizing the cavity resonance, a tunable narrowband MM absorber/emitter for thermophotovoltaic (TPV) is designed and analyzed based on gold nanowire cavities to improve the overall efficiency of TPV systems. Second, a broadband absorber made of ultrathin silica-chromium-silica film working in visible and near-infrared (NIR) range is proposed and demonstrated using impedance transformation method. To further broaden the absorption range and enhance the absorption performance, another broadband absorber covering the visible and near-infrared (NIR) is proposed firstly utilizing the combination of the multilayer impedance match in the short wavelength range and the double resonances in the long wavelength range. Finally, an ultra-broadband multilayer waveguide absorber is designed and studied via the stop light trapped at different waveguide width. The stop light mode is analyzed based on the waveguide mode theory considering the guided forward mode and backward mode at the same waveguide width positionÔÇŁ--Abstract, page iv

    Infrared perfect absorber based on nanowire metamaterial cavities

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    An infrared perfect absorber based on gold nanowire metamaterial cavities array on a gold ground plane is designed. The metamaterial made of gold nanowires embedded in alumina host exhibits an effective permittivity with strong anisotropy, which supports cavity resonant modes of both electric dipole and magnetic dipole. The impedance of the cavity modes matches the incident plane wave in free space, leading to nearly perfect light absorption. The incident optical energy is efficiently converted into heat so that the local temperature of the absorber will increase. Simulation results show that the designed metamaterial absorber is polarization-insensitive and nearly omnidirectional for the incident angle.Comment: 3 pages, 4 figure

    Ultra-Broadband Infrared Absorption by Tapered Hyperbolic Multilayer Waveguides

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    Ultra-broadband strong absorption over 92% covering the infrared wavelength range of 1 ~ 6╬╝m is demonstrated by using the tapered hyperbolic Au-SiO2 multilayer waveguides on glass substrates. Such broadband absorption is formed by the stop-light modes at various wavelengths located at different waveguide widths. A planar hyperbolic waveguide model is built to determine the stop-light modes by considering both forward and backward guided modes. The stop-light modes located inside the Au-SiO2 multilayer waveguide are simulated at the absorption peaks by reducing the Au loss. Tapered multilayer waveguides with varying top widths are further simulated, fabricated and measured, indicating the almost linear relation between the waveguide width and the stop-light wavelength. Moreover, the broadband absorption of tapered waveguide is proved to be angle-insensitive and polarization-independent, and the heat generation and temperature increase are also discussed

    Experimental realization of epsilon-near-zero metamaterial slabs with metal-dielectric multilayers

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    Epsilon-near-zero (ENZ) metamaterial slabs at visible frequencies based on metal-dielectric multilayers are experimentally realized. Transmission, reflection and absorption spectra are measured and used to determine the complex refractive indices and the effective permittivities of the ENZ slabs, which agree with the results obtained from both the numerical simulations and the optical nonlocalities analysis. Furthermore, light propagation in ENZ slabs and directional emission from ENZ prisms are also analyzed. The accurate determination of the ENZ wavelength for metal-dielectric multilayer metamaterial slabs is important for realizing many unique applications, such as phase front manipulation and enhancement of photonic density of states.Comment: 9 pages, 5 figure

    Fabrication of Asymmetric Nanostructures for Plasmonic Force Propulsion

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    The objective of this research is to manufacture and investigate the characteristics and use of asymmetric, metallic, nanostructures for plasmonic force propulsion, a developing method of nano-/picosatellite thrust generation. Visible to near-infrared light is focused onto sub-wavelength nanostructures to generate polarized oscillations of electrons on the surface of the metallic nanostructures (surface plasmon polaritons). The surface plasmon polaritons accelerate nanoparticle propellant away from the nanostructure, creating thrust. Previous numerical simulations have shown that asymmetric nanostructures can resonate strongly within the visible spectrum. This is the first experiment ever attempted and first to successfully demonstrate this resonance where the resonance peak is ╬╗ = 830 nm. The resonance peak of the experimental optical characterization agrees well with our computed model, showing an 11.2% difference. However, the off resonance behavior exhibits peak broadening where the variation of intensity with wavelength, off resonance, has an experimental slope that is 3.7 times less steep than the computed model. Furthermore, the optical transmittance of the sample is 2.1 times higher than computationally modeled. It is shown that the nanostructures are thermodynamically stable in the projected environmental conditions and have an equilibrium temperature of 746.4 K. Upon review of the experimental optical setup, we conclude that thrust generation is not possible with continuous irradiation of light and propose a method of synchronous dynamic acceleration of nanoparticle propellant by use of a pulsed light beam

    Optimizing Height and Packing Density of Oriented One-Dimensional Photocatalysts for Efficient Water Photoelectrolysis

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    Dependences of water-photoelectrolysis efficiency on heights and packing densities of vertically arrayed ZnO nanorods (NRs) and ZnO microrods (MRs) were systematically studied for the first time over a wide range of light incidence angles, under the direction of nanooptics simulation. In the photoelectrolysis, dense NRs of 1.8 ╬╝m in height afforded the highest photocatalytic efficiencies, and further increases of the height kept lowering down the photocatalytic efficiencies, while sparse MRs taller in height consistently afforded better electrolyte penetration and higher photocurrent densities especially at higher angles of incident light. The experimental results are in line with the nanooptics simulation. This new finding is generally applicable to advancing solar-energy conversions, optics, and optoelectronics using oriented one-dimensional micro/nanocrystallites

    Optimizing Height and Packing Density of Oriented One-Dimensional Photocatalysts for Efficient Water Photoelectrolysis

    No full text
    Dependences of water-photoelectrolysis efficiency on heights and packing densities of vertically arrayed ZnO nanorods (NRs) and ZnO microrods (MRs) were systematically studied for the first time over a wide range of light incidence angles, under the direction of nanooptics simulation. In the photoelectrolysis, dense NRs of 1.8 ┬Ám in height afforded the highest photocatalytic efficiencies, and further increases of the height kept lowering down the photocatalytic efficiencies, while sparse MRs taller in height consistently afforded better electrolyte penetration and higher photocurrent densities especially at higher angles of incident light. The experimental results are in line with the nanooptics simulation. This new finding is generally applicable to advancing solar-energy conversions, optics, and optoelectronics using oriented one-dimensional micro/nanocrystallites. ┬ę 2013 American Chemical Society
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