American Physical Society, Physical Review Letters, 21(109), 2012
DOI: 10.1103/physrevlett.109.217401
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We demonstrate experimentally that the energy from a highly localized free-electron-beam excitation can be converted via a planar plasmonic metamaterial to a low-divergence free-space light beam. This emission, which emanates from a collectively oscillating coupled metamolecule nanoantenna ensemble much larger in size than the initial excitation, is distinctly different from cathodoluminescence and bears some similarity with laser light. It offers a novel, flexible paradigm for the development of scalable, threshold-free light sources.