Among the demonstrated metasurfaces, geometric metasurfaces (GMs), consisting of anisotropic meta-atoms with identical geometric parameters and spatially varying orientations, provide an orientation-controlled and dispersion-less phase control over the entire 2 π range for cross-circular polarization (CP) light 31. Applying the concept of PMs to these plasmonic devices and systems can further enhance their functionalities and performance, particularly in applications where plasmonics have unique advantages, such as superlens 24, quantum plasmonics 25, nonlinear optics 26, photovoltaics 27, nanolithography 28, sensing 29, life sciences, and medical applications 30 (see the more detailed discussion on the advantages of PMs in the Supplementary Information). Moreover, over the past two decades, the field of plasmonics has undergone significant advances and enabled a wide range of practical applications 21, 22, 23. Furthermore, PMs have an ultrathin thickness on the order of tens of nanometers, are easy to fabricate, support a field confinement beyond the diffraction limit, and have potential to respond on the timescale of a few femtoseconds 21 these properties are unparalleled in traditional optical elements and cannot be easily extended to dielectric metasurfaces. PMs promise a paradigm shift in optics by replacing traditional bulky optical elements, e.g., beam deflectors 3, 4, 5, 6, lenses 7, 8, 9, 10, waveplates 11, 12, vortex generators 13, 14, 15, 16, and holograms 17, 18, 19, 20 with ultrathin, lightweight, and easy-to-integrate two-dimensional optical interfaces. Plasmonic metasurfaces (PMs) are two-dimensional arrays of metallic nanoantennas (meta-atoms) with subwavelength thicknesses and spacings and a spatially varying phase response 1, 2. We highlight the technological relevance of our plasmonic metasurface by demonstrating a transmission-type beam deflector and hologram with record efficiencies. The proposed metasurface is broadband, versatile, easy to fabricate, and highly tolerant to fabrication errors. In addition, the design of the metasurface proposed in this study introduces an air gap between the antennas and the surrounding media that confines the field within the gap, which mitigates the crosstalk between meta-atoms and minimizes metallic absorption. The efficiency is augmented by breaking the scattering symmetry due to simultaneously approaching the generalized Kerker condition for two orthogonal polarizations. Here, we report a multipole-interference-based transmission-type geometric plasmonic metasurface with a polarization conversion efficiency that reaches 42.3% at 744 nm, over 400% increase over the state of the art. The state-of-the-art efficiency of geometric plasmonic metasurfaces at visible and near-infrared frequencies, for example, is ≤10%. However, the technological relevance of plasmonic metasurfaces operating in the transmission mode at optical frequencies is questionable due to their limited efficiency. In particular, plasmonic metasurfaces feature ultrathin thicknesses, ease of fabrication, field confinement beyond the diffraction limit, superior nonlinear properties, and ultrafast performances.
Metasurfaces are two-dimensional nanoantenna arrays that can control the propagation of light at will.
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