Near-field observation of guided-mode resonances on a metasurface via dielectric nanosphere excitation

We study laser-induced guided-mode resonances on an ultrathin anisotropic metallic metasurface using direct near-field mapping. Coupling of the incident light to the guided-mode resonances is provided by a resonant laser-printed silicon nanosphere placed on the metasurface using nanomanipulation under electron-beam supervision. To visualize the propagation of the guided modes, we employ scattering-type scanning near-field optical microscopy in the near-infrared region (850 nm). The guided-mode resonances excited by the nanosphere demonstrate vanishing anisotropy due to weak confinement at the metasurface/air interface. We also extract the wavenumber of the observed modes through Fourier transformation of the measured near-field maps and find it to be in good agreement with numerical calculations.