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Abstract
We report ultra-broadband perfect absorbers for visible and near-infrared applications that are based on multilayers of metal-insulator (MI) stacks fabricated employing straightforward layer deposition techniques and are, therefore, lithography-free and large-scale compatible. We scrutinize the impact of different physical parameters of an MIMI absorber structure with analysis of each contributing metal layer. After obtaining the optimal design parameters (i.e. material selection and their thicknesses) with both simulation and numerical analysis (Transfer Matrix Method) methods, an experimental sample is fabricated and characterized. Our fabricated MIMI absorber consists of an optically thick tungsten (W) back reflector layer followed by 80 nm aluminum oxide (Al2O3), 10 nm titanium (Ti), and finally another 80 nm Al2O3. The experimental results demonstrate over 90 percent absorption between 400 nm and 1640 nm wavelengths that is optimized for ultra-broadband absorption in MIMI structures. Moreover, the impedance matching method with free-space is used to shed light on the metallic layer selection process.
Highlights
One of the most prominent results that gained attention for Fabry-Perot cavity absorbers was reported by Kats et al in which nanometer thick anti-reflection coatings (ARC) resulted in absorption in a simple two-layer structure[12]
In the afore-mentioned studies of MIMI absorbers, it is taken for granted that the bottom metal layer only functions as a reflector and could be any reflecting metal and the absorption mainly takes place in the middle thin metal
There is a recent report in which multi thickness versions of MIMI absorbers are designed to obtain enhanced broadband absorption[20]
Summary
Sina Abedini Dereshgi[1,2], Amir Ghobadi 1,2, Hodjat Hajian[2], Bayram Butun 2 & Ekmel Ozbay[1,2,3,4]. We report ultra-broadband perfect absorbers for visible and near-infrared applications that are based on multilayers of metal-insulator (MI) stacks fabricated employing straightforward layer deposition techniques and are, lithography-free and large-scale compatible. One group of prominent absorbers are periodically stacked metal insulator Fabry-Perot structures with lossy thin metals that are lithography-free and applicable to large areas and require rather few different types of materials to be deposited. These structures exhibit extended bandwidth into mid-infrared (MIR) when the number of MI layers is increased. After securing the lossiest metal, we have adapted the impedance transfer method where the equivalent impedance is matched to that impedance of air to attain the ideal permittivity values of a bottom metal
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