Highly efficient broadband ultrafast plasmonics.

To date, considerable experimental and theoretical focus has been placed on the spatial control of Surface Plasmon Polaritons (SPPs) using nanostructured surfaces; however, research aimed toward accessing the ultrafast dynamics of SPPs remains vastly unexplored. Despite this, SPPs have the potential to exhibit some of the fastest possible optical processes, while maintaining the advantage of nanoscale spatial manipulation. Here, we present an experimental and computational investigation of a system that provides access to the efficient excitation of broadband, propagating SPP modes. To achieve this, a surface array of tailor designed, reduced symmetry nanostructures has been fabricated to enable the required control of the plasmon dispersion map to match sub 20 fs pulses in the near infra-red. Using a combination of optical spectroscopy and frequency resolved optical gating techniques, complimented by finite element computational analysis, the efficient excitation of propagating broadband plasmonic modes is demonstrated.