Duplicating Plasmonic Hotspots by Matched Nanoantenna Pairs for Remote Nanogap Enhanced Spectroscopy.

Plasmonic nanoantennas are capable of reversibly interconverting free-space radiation with localized modes at the nanoscale. However, optical access to a single nanoantenna, through a laser beam, is always accompanied by disruptive background perturbations and heating effects. Remote spectroscopy is one promising route to overcome these effects. Here, we demonstrate excitation-collection-separated enhanced spectroscopy using a matched nanoantenna pair. The receiving and transmitting antennas are geometrically separated but bridged by the propagating surface plasmon polaritons (SPPs) on the metal film. The receiving antenna, consisting of a silver nanowire on a mirror, ensures a high light-to-plasmon conversion efficiency. The transmitting antenna consists of a silver nanocube over a mirror and is impedance matched to free space photons and the propagating SPPs. As a proof-of-principle, we demonstrate remote surface-enhanced Raman scattering with a high signal-to-noise ratio. This matched nanoantenna pair may have applications for remote entanglement of quantum emitters, biochemistry detection, or optical interconnects.