Near Field Scanning Microscopy has great potential in the study and characterization of 3D and 2D plasmonic metamaterials and metasurfaces.   In this paper, a Nanonics MultiView 4000 Dual probe Near-field Scanning Optical Microscope was used to investigate two phenomena in plasmonic metasurfaces (subwavelength antenna like pattern in ultrathin silver film) showing:

  1. Extraordinary suppressed transmission ( EOST) in metasurfaces

  2. Bright (radiative) and dark (non-radiative) plasmonic modes propagation in metasurfaces

The Nanonics MultiView 4000 Scanning Probe Microscope is ideally suited for complete characterization of the dark mode propagation.  One NSOM probe injects the light to excite the dark (non-radiative) modes, while the second NSOM probe scans in the vicinity of the illumination probe, and detects the dark modes distribution.

The NSOM results obtained demonstrate that far-field radiation resonantly excites antenna-like (bright) modes that are localized on the metal ridges. The re-radiation of these modes into far-field interferes destructively with the transmitted wave, thus almost completely suppressing transmission.  In contrast, a second type of mode, (dark) bound mode Surface Plasmon Polarities (SPPs) launched from the NSOM tip, propagate well across the metasurface, preferentially perpendicular to the grating lines.

Idea in Brief: It was shown that dark modes cannot be excited in the far-field, and instead NSOM tips are the best source for excitation and probing of the non-radiative modes, which do not interact with the far-field.  




Published:  Advanced Optical Materials, 2014, S. Dobmann et al.

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