Photoelectron imaging of modal interference in plasmonic whispering gallery cavities
We use three-photon photoemission electron microscopy (PEEM) to investigate the interference of coherently excited dipolar and quadrupolar resonant modes of plasmonic whispering gallery resonators formed by circular grooves patterned into a flat Au surface. Optical scattering and cathodoluminescence spectroscopy are used to characterize the cavity resonance spectra for a wide range of cavity radii and groove depths. Using PEEM, we directly resolve the interference between the modal field distribution of dipolar and quadrupolar modes that are coherently excited at λ = 795 nm under oblique incidence. Characteristic asymmetries in the photoelectron images for both TM and TE excitation are a direct consequence of the coherent excitation of the resonant modes.
Melchior, P, Kilbane, D, Vesseur, Ernst Jan R, Polman, A, & Aeschlimann, M. (2015). Photoelectron imaging of modal interference in plasmonic whispering gallery cavities. Opt. Express, 23(25), 31619–31626. doi:10.1364/OE.23.031619