Shaping plasmonic light beams with near-field plasmonic holograms

摘要

Surface-plasmon waves have been utilized in many applications such as biological and chemical sensing and trapping, sub-wavelength optics, nonlinear optics, optical communication and more. Controlling the shape and trajectory of these waves is a key feature in enabling all of the above applications, and a challenging task. The fundamental challenges resides in the different wave properties of surface plasmon waves, with comparison to free-space waves: First, coupling a surface plasmon wave from a free-space wave requires a compensation for the missing momentum between the two wave-vectors. Second, owing to the limited propagation length of surface plasmons and the limited measurement range of their characterization tools, the resulting beams should be formed directly in the near-field. Third, unlike planar phase plates, surface plasmons are excited over a finite propagation distance and therefore their phase cannot be simply defined at a specific one-dimensional plane. Fourth, dynamic tools for controlling the wavefront of free-space beams, like spatial-light-modulators, do not exist for surface plasmons. Here we demonstrate, both numerically and experimentally, a robust holographic scheme that provides complete control over the amplitude and phase of surface-plasmons, thereby enabling the engineering of any desired plasmonic light beam. We show how all of the above challenges can be overcome by introducing a new class of binary plasmonic holograms, which are designed specifically for the near-filed. We demonstrate a large variety of plasmonic beams, such as "self-similar", "non-diffracting", "self-accelerating", "self-healing", paraxial and non-paraxial plasmonic beams, and also the dynamic generation of plasmonic bottle-beams for micromanipulation of particles.