Abstract
We propose and demonstrate a novel photonic-plasmonic antenna capable of confining electromagnetic radiation at several mid-infrared wavelengths to a single sub-wavelength spot. The structure relies on the coupling between the localized surface plasmon resonance of a bow-tie nanoantenna with the photonic modes of surrounding multi-periodic particle arrays. Far-field measurements of the transmission through the central bow-tie demonstrate the presence of Fano-like interference effects resulting from the interaction of the bow-tie antenna with the surrounding nanoparticle arrays. The near-field of the multi-wavelength antenna is imaged using an aperture-less near-field scanning optical microscope. This antenna is relevant for the development of near-field probes for nanoimaging, spectroscopy and biosensing.
Highlights
Infrared near-field imaging and spectroscopy are emerging as powerful tools for the understanding of the structure and chemistry of materials at the nanoscale
These applications typically rely on the use of scattering-type scanning near-field optical microscopy (s-SNOM) [4,5,6,7], where the diffraction limit is overcome by the use of a sharp atomic force microscope (AFM) tip acting as an antenna to concentrate the incident radiation to nanoscale volumes
Following a design strategy recently proposed for multi-wavelength plasmonic nanoantennas in the visible range [11], we present here a design based on embedding a single bow-tie nanoantenna in an array of scattering nanoparticles that funnel incident radiation into the central gap of the bow-tie
Summary
Infrared near-field imaging and spectroscopy are emerging as powerful tools for the understanding of the structure and chemistry of materials at the nanoscale. The ability to use a spectrally broad source in such systems allows for the use of Fourier-transform infrared (FTIR) spectroscopy techniques at the nanoscale for the chemical identification of unknown nanostructures These applications typically rely on the use of scattering-type scanning near-field optical microscopy (s-SNOM) [4,5,6,7], where the diffraction limit is overcome by the use of a sharp atomic force microscope (AFM) tip acting as an antenna to concentrate the incident radiation to nanoscale volumes. We demonstrate the possibility to achieve multi-frequency operation by using nested particle arrays with multiple periodicities Such multiple-wavelength single-focus structures implemented on the facet of a chalcogenide fiber [12] would enable the realization of a fiber-based multi-channel infrared scanning optical microscope by providing efficient focusing of the incident fiber-mode field into the nanoscale gap of the central bow-tie, while suppressing alignment sensitivity. Differently from antenna arrays with periodic or aperiodic geometries featuring a high-density of hot-spots embedded in a background of photonic-plasmonic modes [13,14,15,16,17,18], the proposed single hot-spot structure benefit from enhanced spatial resolution due to the large contrast between the field enhancement at the gap of a bow-tie antenna and at the edges of the metallic nanoparticles surrounding the isolated hot-spot
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