The interaction of a focused beam with a metasurface supporting dark modes is investigated. We show computationally and experimentally that the excitation of dark modes is accompanied by characteristic changes in the reflected Fourier spectrum. This spatial frequency filtering capability indicates an avenue for the all-optical, on-chip detection of phase gradients for biological and other imaging techniques.

The influence of the near-field probe-tip on a model sample consisting of one-dimensional apertures is investigated using scanning near-field optical microscopy (SNOM). We use finite-difference time-domain (FDTD) simulations combined with SNOM scans to show that the probe-tip has a rather profound effect on the shape of the measured transmission intensity profiles. By taking into account the near-field perturbations introduced by the probe, our newly developed FDTD model facilitates the quantitative analysis of SNOM data and provides new insights into near-surface, subwavelength optical interactions.

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