Absorption of light by plasmonic devices

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Copyright: Haque, Ahasanul
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Abstract
Plasmonic is an emerging technology used to increase the performance of thin-film devices via light-trapping mechanisms. Recently, plasmonic devices have been used due to their nanoscale fabrication abilities. Metamaterials are promising candidates for improving the light absorption of plasmonic devices. The extraordinary properties of metamaterial-plasmonic devices (such as the perfect absorption of light) open up applications such as solar energy harvesting, photo-detecting and making batteries. This thesis focuses on the theoretical design and experimental studies of metamaterial-based perfect absorbers (MMPA) to improve their optical properties and applications (e.g., energy harvesting). I also design a high-power MMPA for high-power laser applications. First, I present the design and analysis of a high-power broadband perfect absorber. An array of rectangular patterns was placed to broaden the bandwidth so that the array can function between 950 nm and 1400 nm. Here, I propose a tungsten boride (a refractory ceramic) broadband metamaterial absorber and characterize its optical properties numerically and experimentally. I have also analyzed the damage characteristics of this absorber using a femtosecond laser and compared these with an ordinary gold metamaterial absorber. Second, a multilayer-based perfect absorber for omnidirectional capabilities is theoretically and experimentally analyzed. The device provides a reasonable amount of light absorption and thermal stability has been checked. Applying this device to high-temperature solar cell applications is discussed. I demonstrate a thermally stable broadband absorber based on an ultrathin layer of refractory ceramic, tungsten boride. I experimentally analyze and compare the performance of the absorber with an aluminum-based absorber. The multilayer perfect absorber has absorption higher than 85% in the wavelength range between 500 and 1600 nm over a large range of incident angles (up to 60 degrees). I show that a tungsten boride absorber has significantly better temperature stability compared to its aluminum counterpart, achieving stable operation at temperatures up to 270 ℃. These absorbers may have applications in solar thermophotovoltaic energy conversion. Third, a square hole structure is proposed, where a lossless silica dielectric material is combined with MnO2 materials. Then, the geometric parameters of this structure are numerically optimized at the desired application. An adequate choice of parameters, shape and the proper combination of materials can lead to an electrically tuneable metasurface. The structure can produce a 25% change of transmission with the applied electric power. Finally, I numerically analyzed and experimentally characterized Kevlar fabrics for the application of personal heat management. Heat management is essential for human comfort. In recent years, passive radiative cooling through heat transfer to outer space has been extensively studied. Personal temperature control is used to control the temperature of objects beyond the local environmental temperature. I show that Kevlar fabrics are transparent to mid-infrared human body radiation but opaque to visible light. Here, I have experimentally investigated the optical and thermal properties of Kevlar fabrics, which can have 90% emissivity in the mid-infrared region and produce a 2.6 ℃ temperature drop. I processed a Kevlar textile that promotes effective radiative cooling while retaining sufficient air permeability, water-wicking rate, and mechanical strength for wearability. The Kevlar fabric is an effective and scalable textile for personal thermal management.
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Haque, Ahasanul
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Publication Year
2021
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Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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