Optically active surfaces that can provide strong localization of electromagnetic fields at predefined points are desired for applications that require high spatial resolution and high sensitivity. Here, we examine the geometric influences on, and polarization dependencies of, electromagnetic near fields on the surface of an array of tailor designed, mesoscalic, silver-coated structures with threefold symmetry characteristics. For spatially resolved mapping of the electromagnetic near fields and examining the influence of polarization, we use a photoelectron emission microscope. We find that the investigated structures not only provide an increase of the near-field intensity at their boundaries, but also that the symmetry centers of the structures focus energy in a polarization dependent manner. Changing the polarization of the incident light enables the localization of near-field intensities without displacing the excitation. Hence we show that breaking of symmetry can provide controllable centers of “hot spots” for the basis of an improved design to gain more efficient surface structures.
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