The Focusing and Talbot Effect of Periodic Arrays of Metallic Nanoapertures in High-Index Medium

Three finite-sized two-dimensional (2D) periodic arrays of metallic nanoapertures with the shape of nanowave, nanohole, and nanodot have been developed. Using water as an output medium, although the operating wavelengths are larger than the array period, both the focusing and far-field plasmon Talbot effect are experimentally observed, showing a good agreement with the 2D finite-difference time-domain (FDTD) simulation results. The focusing performance in both cases, with the output medium of air and of water, is compared. A detailed investigation of the plasmon Talbot revivals reveals that they are composed of subwavelength hotspots with the size of ∼0.5λ distributed in the same array period as the original device. Three-dimensional FDTD simulations prove that the existence of surface plasmons (SPs) exhibits an enhanced optical transmission at some SP resonant wavelengths dependent on the output medium. Additionally, it is demonstrated that the Talbot revivals provide a high-resolution mean to distinguish the slight geometric nonuniformity in periodic nanostructures.