We resolve the resonant whispering gallery modes of plasmonic subwavelength ring cavities defined by circular grooves patterned into a gold surface. An interesting interplay is observed between subwavelength confinement and guiding along the groove. Full spatial and spectroscopic information is directly obtained using cathodoluminescence, including details of the nanoscale intensity distribution (spatial resolution 11 ± 8 nm). Excellent agreement between measurements and rigorous electromagnetic theory is obtained, thus allowing us to assess the symmetry, ordering, degree of confinement, and near-field enhancement of the modes with unprecedented detail.

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Persistent URL dx.doi.org/10.1021/nl9012826
Journal Nano Lett.
Vesseur, Ernst Jan R, García de Abajo, F.J, & Polman, A. (2009). Modal decomposition of surface-plasmon whispering gallery resonators. Nano Lett., 9, 3147–3150. doi:10.1021/nl9012826