Near-field probing of surface plasmon polariton formation in imprinted gold nanoisland arrays

Large-area imprinting stamps with nanometer-scale features are a rapidly developing area of research in plasmonics. In integrated photonic structures, surface plasmon (SPs) and surface plasmon polaritons (SPPs) are tuned by selecting both the appropriate wavelength and the angle of incidence of the excitation light. The resulting exponential fields can be studied by an optical technique such as scanning near-field optical microscopy (SNOM). Here, we report on the application of the aperture-type SNOM technique to characterize, at nanoscopic and microscopic scales, the formation of the SPPs and the beat pattern formed with the superposition of SPs and the effective component of the probing light formed in discrete metallic nanostructures of Au fabricated on imprinting stamps. We discuss a model to describe the beat pattern in terms of this superposition and demonstrate that the dominant SPs have a transverse nature. Our experiments are supported by modeling the optical response and near-field in gold nanostructures using the simulation tool Tidy3D. Our results provide a straightforward way to investigate and characterize SPPs at the nanostructure level.