Interaction of light with a nanoapertured metal film has been the subject of extensive study because it produces many interesting phenomena, such as "enhanced" transmission of light through a nanohole array or shaping the spatial or spectral profiles of the transmitted light. The richness of the phenomena stems from the complexity of the way that light interacts with the nanostructures formed in the metal film. Surface plasmons (SPs), collective oscillation of electrons carrying the electromagnetic energy in the form of photons trapped at a metal/dielectric interface, can effectively mediate the interactions between metal nanostructures. Unlike the dielectric case, a metal wedge structure can also efficiently interact with free-space radiation, diffracting an incident light and/or coupling the light into surface plasmons (vice versa, decoupling surface plasmons into free-space radiation). We show that the diffraction by a metal corner plays an essential role in exciting surface plasmons and shaping energy flow distributions (enhancement or depletion). The phase relationship of the boundary diffraction and planar incident waves is extracted from measurement and simulation results. A single nanoaperture formed in a metal film is a simple and yet one of the most fundamental structures that can be viewed as a basic building block of aperture-based nano-plasmonic structures. In this study we have investigated the characteristic evolution of optical wavefronts emanating from a nanoslit formed in a thin silver film. A planar wave, directly transmitted through the thin metal film, was used as a reference in forming an interference pattern with the slit-transmitted free-space radiation and surface plasmons, and a scanning probe technique was employed in imaging the interference pattern in the near- to far-field regimes. Both the amplitude and phase information of the slit-transmitted waves with respect to the direct film-transmitted wave were extracted from the experimental data, and the results are compared with the analytical and numerical simulation results. The near- to far-field imaging of optical wavefronts is expected to be important in designing advanced nano-optic and plasmonic structures where precise control of both phase and amplitude of an optical signal is essential. We have also investigated grating diffraction with order-selection capability. This method offers a promising approach to accessing angular ranges that have not been reachable in conventional optics and to overcoming the limits of conventional refractive optics.
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