Focusing surface plasmon polaritons through a disordered nanohole structure

Control of near-field waves is the key to going beyond the diffraction limit. Here we present the focusing of plasmonic waves, a type of near-field waves, by the wavefront shaping of far-field waves. We coupled far-field illumination to a disordered nanoholes on a thin gold film to generate speckled plasmonic waves. By controlling the phase pattern of the incident waves at the excitation wavelength of 637 nm, we demonstrated the focusing of surface plasmon polaritons (SPPs) down to 170 nm at arbitrary positions. Our study shows the possibility of using disordered nanoholes as a plasmonic lens with high flexibility in the far-field control.