We present an experimental and theoretical study of Babinet’s principle of complementarity in plasmonics. We have used spatially-resolved electron energy loss spectroscopy and cathodoluminescence to investigate electromagnetic response of elementary plasmonic antenna: gold discs and complementary disc-shaped apertures in a gold layer. We have also calculated their response to the plane wave illumination. While the qualitative validity of Babinet’s principle has been confirmed, quantitative differences have been found related to the energy and quality factor of the resonances and the magnitude of related near fields. In particular, apertures were found to exhibit stronger interaction with the electron beam than solid antennas, which makes them a remarkable alternative of the usual plasmonic-antennas design. We also examine the possibility of magnetic near field imaging based on the Babinet’s principle.

Optical metasurfaces have emerged as a new generation of building blocks for multi-functional optics. Design and realization of metasurface elements place ever-increasing demands on accurate assessment of phase alterations introduced by complex nanoantenna arrays, a process referred to as quantitative phase imaging. Despite considerable effort, the widefield (non-scanning) phase imaging that would approach resolution limits of optical microscopy and indicate the response of a single nanoantenna still remains a challenge. Here, we report on a new strategy in incoherent holographic imaging of metasurfaces, in which unprecedented spatial resolution and light sensitivity are achieved by taking full advantage of the polarization selective control of light through the geometric (Pancharatnam-Berry) phase. The measurement is carried out in an inherently stable common-path setup composed of a standard optical microscope and an add-on imaging module. Phase information is acquired from the mutual coherence function attainable in records created in broadband spatially incoherent light by the self-interference of scattered and leakage light coming from the metasurface. In calibration measurements, the phase was mapped with the precision and spatial background noise better than 0.01 rad and 0.05 rad, respectively. The imaging excels at the high spatial resolution that was demonstrated experimentally by the precise amplitude and phase restoration of vortex metalenses and a metasurface grating with 833 lines/mm. Thanks to superior light sensitivity of the method, we demonstrated, for the first time to our knowledge, the widefield measurement of the phase altered by a single nanoantenna, while maintaining the precision well below 0.15 rad.

Coherence-controlled holographic microscopy (CCHM) is a realtime, wide-field, and quantitative light-microscopy technique enabling 3D imaging of electromagnetic fields, providing complete information about both their intensity and phase. These attributes make CCHM a promising candidate for performance assessment of phase-altering metasurfaces, a new class of artificial materials that allow to manipulate the wavefront of passing light and thus provide unprecedented functionalities in optics and nanophotonics. In this paper, we report on our investigation of phase imaging of plasmonic metasurfaces using holographic microscopy. We demonstrate its ability to obtain phase information from the whole field of view in a single measurement on a prototypical sample consisting of silver nanodisc arrays. The experimental data were validated using FDTD simulations and a theoretical model that relates the obtained phase image to the optical response of metasurface building blocks. Finally, in order to reveal the full potential of CCHM, we employed it in the analysis of a simple metasurface represented by a plasmonic zone plate. By scanning the sample along the optical axis we were able to create a quantitative 3D phase map of fields transmitted through the zone plate. The presented results prove that CCHM is inherently suited to the task of metasurface characterization. Moreover, as the temporal resolution is limited only by the camera framerate, it can be even applied in analysis of actively tunable metasurfaces.