Broadband Focusing Flat Mirrors Based on Plasmonic Gradient Metasurfaces

• Published in: Nano letters Vol. 13; no. 2; pp. 829 - 834
• Main Authors: Pors, Anders, Nielsen, Michael G, Eriksen, René Lynge, Bozhevolnyi, Sergey I
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 13.02.2013
• Subjects: Beams (radiation); Broadband; Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Deposition; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Flats; Focusing; Gold; Materials science; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Physics; Plasmonics; Surface and interface electron states; Tuning; Metasurfaces; metamaterials; plasmonics; Fresnel mirror; gap surface plasmons; Thin films; Gold; Silicon oxides; Focusing; Thick films; Plasmons; Mirrors; Nanostructured materials
• ISSN: 1530-6984; 1530-6992; 1530-6992
• DOI: 10.1021/nl304761m

We demonstrate that metal–insulator–metal configurations, with the top metal layer consisting of a periodic arrangement of differently sized nanobricks, can be designed to function as broadband focusing flat mirrors. Using 50-nm-high gold nanobricks arranged in a 240-nm-period lattice on the top of a 50-nm-thick layer of silicon dioxide deposited on a continuous 100-nm-thick gold film, we realize a 17.3 × 17.3 μm2 flat mirror that efficiently reflects (experiment: 14–27%; theory: 50–78%) and focuses a linearly polarized (along the direction of nanobrick size variation) incident beam in the plane of its polarization with the focal length, which changes from ∼15 to 11 μm when tuning the light wavelength from 750 to 950 nm, respectively. Our approach can easily be extended to realize the radiation focusing in two dimensions as well as other optical functionalities by suitably controlling the phase distribution of reflected light.