Abstract
The high fractional open area of metal thin film coatings, with two dimensional, hexagonally ordered, close packed arrays of holes, makes them of interest for the incorporation of plasmonic effects into a variety of optical devices. Gold films with hexagonal patterns of circular holes have been created on ZnSe infrared windows. The films have 2.50 μm diameter holes and a hexagonal lattice parameter of 3.06 μm which places the primary transmission resonances of the ZnSe/gold interface at ~1,400 cm−1 (7.14 μm) and that of the air/gold interface at ~3,800 cm−1 (2.63 μm). This geometry produces useful transmission across the whole traditional mid-infrared range. The dispersion of these resonances has been measured by changing the angle of incident light. The data is modeled with explicit momentum matching equations in two different, high symmetry geometries, allowing the effective index of refraction to vary with wavelength. The response of these resonances to the addition of an acetaldehyde coating is described.
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