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Inter-slit Coupling in Gold Film Hole Arrays

Inter-slit interactions across one-dimensional arrays of sub-micro meter rectangular holes in gold films are explored. Using electron energy loss spectroscopy combined with scanning transmission electron microscopy, a series of cavity standing waves is resolved, indicating particularly high interslit interactions, about an order of magnitude larger than the intra-slit edge to edge coupling. Pronounced signal enhancements are thus induced, dominated by short-range interactions and high mode-localization, while yet, relatively long-range coherence is retained. The sub-nm electron beam, in spite of principal differences from broad-area probes, yields results similar to extraordinary optical transmission (EOT). Implications to EOT mechanisms, including its sub-wavelength, off-resonance limit, are pointed out.