Extraordinarily transparent compact metallic metamaterials
Abstract
7 pags., 6 figs., -- Open Access funded by Creative Commons Atribution Licence 4.0 ; The design of achromatic optical components requires materials with high transparency and low dispersion. We show that although metals are highly opaque, densely packed arrays of metallic nanoparticles can be more transparent to infrared radiation than dielectrics such as germanium, even when the arrays are over 75% metal by volume. Such arrays form effective dielectrics that are virtually dispersion-free over ultra-broadband ranges of wavelengths from microns up to millimeters or more. Furthermore, the local refractive indices may be tuned by altering the size, shape, and spacing of the nanoparticles, allowing the design of gradient-index lenses that guide and focus light on the microscale. The electric field is also strongly concentrated in the gaps between the metallic nanoparticles, and the simultaneous focusing and squeezing of the electric field produces strong 'doubly-enhanced' hotspots which could boost measurements made using infrared spectroscopy and other non-linear processes over a broad range of frequencies. ; S.J.P. would like to acknowledge his studentship from the Centre for Doctoral Training on Theory and Simulation of Materials at Imperial College London funded by EPSRC Grant No. EP/L015579/1. R.A.A.-P., N.P.-P., L.G., and M.A.C.-D. thank the MINECO-Spain (CTM2014-58481R, CTM2017-84050R, CTQ2017-88648R, RYC-2015-19107 and RYC2016-20331), Xunta de Galicia (Centro Singular de Investigacion de Galicia, Acc. 2016-19 and EM2014/035), Generalitat de Cataluña (2017SGR883), URV (2017PFR-URV_B2-02), URV and Banco Santander (2017EXIT-08) and European Union (ERDF). X.X. acknowledges the Lee Family Scholarship. S.A.M. and R.V.C. acknowledge the EPSRC Mathematical Fundamentals of Metamaterials programme grant (EP/L024926/1) and the US Air Force Office of Scientific Research/EOARD (FA9550-17-1-0300). S.A.M. additionally acknowledges the Lee-Lucas Chair in Physics and DFG Cluster of Excellence Nanoinitiative Munich, and the Bavarian "Solar Technologies Go Hybrid" (SolTech) programme. R.V.C. thanks the Leverhulme Trust for their support. V.G. acknowledges the Consejo Superior de Investigaciones Cientficas (INTRAMURALES 201750I039).
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