Structured illumination microscopy using extraordinary transmission through sub-wavelength hole-arrays

Structured illumination microscopy, like confocal m icroscopy, is a common way to observe fluorescently stained samples with higher resolutio n than a wide-field microscope. There is only one scanning confocal spot; with multiple spot s faster acquisition is possible. Instead of using a Nipkow disc, however, we use transmission t hrough a metal hole-array. The microscope termed midfield (1) uses a near-field ph enomenon, extraordinary transmission (EOT) of light, for excitation and detects fluoresc ence in far-field. This EOT (2) is different from the prediction by Bethe (3). It has spectral selection in that, for s ome spectral peaks, more light passes through a hole th an impinges on it. There is no total diffraction; the angular spread is limited to a few degrees (4). Whe n the wavelength is shorter than the array period, th e transmission forms an interference pattern. The hig h intensity lobes are positioned above the centers of individual holes or between them. One lobe can be separately imaged from its neighbor because the distance between lobes in the focal plane, dependin g on the array period, is larger than the point sprea d function (PSF) of the imaging lens. This is illustr ated in Figures 1 and 2. It has already been shown with 3D surface plasmon assisted nanolithography (5) that this interference exists. We are currently measuring the predicted interference patterns in our microscope; this will be a direct proof of concept. We present the microscope principle, the expected optical properties, and our experimental results.