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Interaction of near-field microscopy probes with surface plasmon polaritons

In this work, we use a collection-type scanning near-field optical microscope to study the intensity distribution along the direction perpendicular to the interface, considering the interaction of the probe with the evanescent field of surface plasmon polaritons. A decrease of the signal is observed as the probe comes near to contact, as opposed to the expected single exponential increase. This effect is explained with a relatively simple semi-analytical model that takes into account the shape of the tip and the geometrical cutoff of the plasmonic mode. The proposed model confirm the presence of the intensity dip near the surface, as a result of the perturbation of the field caused by the probe.