Phase resolved near-field mode imaging for the design of frequency-selective surfaces.

Frequency-selective surfaces (FSS) are a class of metasurfaces with engineered reflectance, absorbance, and transmittance behavior. We study an array of metallic crossed dipole FSS elements in the infrared using interferometric scattering-type scanning near-field optical microscopy (s-SNOM). We resolve the dependence of the near-field phase on the dimensions of the elements and compare with numerical models. The combined phase and amplitude information of the underlying near-field mode distribution compared to conventional far-field absorption spectroscopy greatly improves the targeted design of frequency-selective surfaces.