Wavefront Shaping for Optimal Extinction of Focused Light by Individual Nanoscatterers

Achieving complete optical extinction by small structures is key for applications such as photodetection and light harvesting, and constitutes a promising solution to the problem of efficient in-and-out coupling of light in nanophotonic devices. In this paper, we provide an innovative solution to this challenge by experimentally demonstrating optimal extinction by individual and arrayed scatterers separated from a planar reflecting surface, by shaping the wavefront of the input light. We fabricate and characterize planar particle arrays of sizes ranging from extended lattices to individual nanoparticles, separated from a planar, partially absorbing surface by a controlled distance. By optimizing the incident wavefront of a tightly focused light beam and the particle–surface separation, we achieve optimal coupling to a single nanoparticle-on-mirror structure. Comparison with theory shows that the optimum incident wavefronts correspond to the time-reversed emission profiles from the nanoscatterer in the presence of the planar reflector. Using these optimal illumination conditions, we demonstrate 70% extinction of a tightly focused beam by a single plasmonic nanoparticle, and up to 90% extinction in sub-wavelength 2 × 2 clusters of nanoparticles on a reflector. These results constitute a solid step toward a practical solution to the in-and-out light coupling problem in nanophotonics.

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