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

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 microm, was chosen for detailed study. Direct imaging of the EOT efficiency simultaneously across the range 0 < kx < 0.001 nm(-1), 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 4-dimensional data set of transmission efficiency with respect to lambda, kx, and n. This technique is compatible with any of the subwavelength aperture array-based chemical sensing methods reported in the literature, however it offers faster transduction of the full spectrum of plasmonic resonant shifts.