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Surface plasmons, metamaterials
The interaction of light with periodic, metallic or dielectric structures has revealed a plethora of fascinating new phenomena and novel ways to tailor light. In the case of metamaterials the structure determines the optical properties with unique consequences like negative refraction and cloaking and a big potential for applications. To facilitate progress in the field, reliable and efficient simulation methods are required. We are currently developing a method based on multiple scattering theory. The method was used to analyze periodic arrays of metal/dielectric/metal nanosandwiches and we have retrieved the effective permittivity and permeability of the structure (Fig 1). Depending on the particular geometry, this system shows negative magnetic permeability as high as -2 at optical frequencies, which is a basic ingredient towards negative refractive index metamaterials. |
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Up: Metal/dielectric/metal nanosandwich arrays on a substrate. The lattice constant (a) ranges from 160 to 250nm and the diameter of the nanodisks is 100nm the heights of metal and dielectric nanodisks are 20 nm. Down: Effective electric permittivity ε and magnetic permeability μ of the structure for a=200nm. The colour plot shows the variation of μ with the lattice constant. Close packed nanosandwiches show high negative μ close to -2. |
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Efficient IR emitters
Patterned metallodielectric structures have interesting optical properties. We have fabricated arrays of holes on a thin (100 nm) film on a Si substrate and transferred the hole pattern using plasma etching into the Si. The final structure is shown in Fig 2 where the diameter of the holes is around 2.5 μm. This structure shows a narrow absorption band in the infrared (~5μm) at wavelengths close to the lattice constant. Strong narrow band absorption means efficient, narrow band IR emission which is shown for different temperatures. Such structures could find applications in thermophotovoltaics where heat is converted to electricity.
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| Last update 20 November 2009 |