Wavevector-resolved monochromatic spectral imaging of extraordinary optical transmission through subwavelength aperture arrays

A technique for wavevector-resolved spectroscopic imaging of extraordinary optical transmission (EOT) is developed and tested. The approach allows a large fraction of the first Brillouin zone to be mapped at a single wavelength, thereby greatly increasing the efficiency of sensitivity mapping experiments. An axially opposed, matched pair of microscope objectives constitutes the core of the apparatus. The condensing lens defines a broad range of wavevectors incident upon the sample, while the second objective with a higher numerical aperture collects all of the light transmitted through the sample. In this way, information related to transmission efficiency over a broad range of in-plane wavevectors is preserved at different spatial coordinates in the final image. A periodically structured gold film, consisting of a square array of cylindrical pores, measuring 90 x 90 pores, 100 nm in diameter, with a lattice constant of 1.1 urn, was chosen for detailed study. Direct imaging of the EOT efficiency simultaneously across the range 0 < k < 0.001 nm, or 20% of the first Brillouin zone, was accomplished, although this was not the limit of the instrument. The experiment was repeated across 21 values of the wavelength and 7 values of the refractive index, to construct a 4dimensional data set of transmission efficiency with respect to λ, κ and n. This technique is compatible with any of the subwavelength aperture arraybased chemical sensing methods reported in the literature, however it offers faster transduction of the full spectrum of plasmonic resonant shifts. ©2009 Optical Society of America.