Nanostructured Broad Band Infrared Absorber
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Nanostructured Broad Band Infrared Absorber Timothy D. Corrigan1, Dong Hun Park2, Dennis Drew3, and Ray Phaneuf2-4 1
Physical Sciences, Concord University, Athens, West Virginia Electrical Engineering, College Park, Maryland 3 Physics, University of Maryland, College Park, Maryland 4 Materials Science, University of Maryland, College Park, Maryland 2
Abstract We describe a near perfect broad band absorber based on a laterally nanostructured multilayer material. We present calculations of the structure that demonstrates over 99% absorption of the 500 K black body spectrum. We also show the ability to manufacture an anti-reflective layer using a nanostructured metamaterial which allows us to tailor the index of refraction using effective medium theory. The absorber can be adapted for use in any frequency range and any source type. These materials may have applications in energy harvesting and scattered light control. INTRODUCTION A blackbody absorber based on a multilayer Bragg reflector, with dielectric layers interspersed with very thin conducting layers is proposed. A key feature is that the thickness of the metal layers is small compared to the skin depth for the metal across the range of frequencies of interest, making the optical properties of each layer insensitive to frequency [1]. Figure 1 shows a schematic of the basic design. Many different materials could serve as the dielectric. However, barium fluoride (BaF2) is particularly attractive candidate for this application as the dielectric because the real component of the index of refraction is close to unity and the imaginary component is very low over a large range of frequency, making it functional for blackbody radiation collection over a wide range of frequencies. In addition, BaF2 is a robust material with a relatively high melting temperature (1368 oC). The metal to be used in the calculations below is Ni/Cr (nickelchrome). As a relatively high resistivity metal it yields a lower admittance than many other metals allowing for good impedance matching to ambient, as demonstrated by the calculated absorption summarized below. It also allows a carrier relaxation rate above 60 THz. Finally, Ni and Cr adhere well to a wide variety of substrates, and are frequently used in deposition of other metals, making this a good choice for fabrication considerations.
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Anti-reflective coating Thin metallic layers
Dielectric layers
Figure 1. Schematic of the multilayer Bragg reflector absorber. METHOD The absorption characteristics of the proposed structure are calculated using MATLAB® software. To obtain the s- and p- reflectance, we use rigorous expressions which account for multiple reflections inside the film as well as angle of incidence, as shown elsewhere [2,3]. Transmission calculations were performed in a similar matter, and then the absorption was calculated using A = 1 – T – R. For the material parameters we assumed the dielectric was BaF2 which has an index of refraction of 1.4 in the IR. The metal layer is an extremely thin film of NiCr (Rsquare~ 2
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