Optical nanoantennae: Enhanced electromagnetic fields and enhanced fluorescence
Paired metallic nanoparticles can show a strong optical resonance that depends strongly upon particle geometry, the gap between adjacent particles, material parameters and electromagnetic polarization. These pairs, often called optical antennae, are able to locally produce enhanced electromagnetic fields along with increased light scattering. ^ Studying ordered particle pairs is fairly new to the community and the topic requires continued growth and development for advanced device applications. The presented research focuses around the development and characterization of nanoantenna arrays that operate in the visible and NIR portion of the spectrum. Our design takes advantage of the gap resonance between two quasi-elliptical gold particles with the gap parallel to the long axis. ^ Arrayed and individual optical antennae have been fabricated via electron beam lithography, metal deposition and subsequent processing. Characterization includes scanning electron microscopy, far-field broadband spectroscopy and near-field scanning optical microscopy. Strong optical resonances are seen for light polarized across the nanoantenna gap. Both near-field and far-field measurements show a high extinction for resonant wavelengths. Optical antennae have been coated with a dye embedded in a dielectric host. The dye’s emission excites the plasmon resonances in the antennae and significant fluorescence enhancement is seen throughout the emission spectra. The enhanced emission exhibits a reduced fluorescence lifetime and is highly polarized. Engineering these interactions between emitters and nanoantennae will prove useful for future device applications in both bio-sensing and nanoscale optoelectronic integration. ^
Vladimir Shalaev, Purdue University.
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