Surface acoustic wave mediated coupling of free-space radiation into surface plasmon polaritons on plain metal films

We propose and demonstrate a surface acoustic wave-driven converter of light into surface plasmon polaritons. An otherwise unstructured thin metal film is deformed by traveling acoustic waves on a piezoelectric substrate underneath. This spatially periodic corrugation enables to bridge the momentum gap between free-space radiation and surface-bound modes. This principle is realized with plain gold films on a LiNbO3 wafer where surface acoustic waves induce surface ripples in the metal. For near-infrared light we observe efficiencies of order 10(-4) for exciting surface plasmon polaritons.