title: k-space imaging of the eigenmodes of sharp gold tapers for scanning near-field optical microscopy.
abstract: We investigate the radiation patterns of sharp conical gold tapers, which were designed as adiabatic nanofocusing probes for scanning near-field optical microscopy (SNOM). Field calculations show that only the lowest order eigenmode of such a taper can reach the very apex and thus induce the generation of strongly enhanced near-field signals. Higher-order modes are coupled into the far field at finite distances from the apex. Here, we demonstrate experimentally how to distinguish and separate between the lowest and higher-order eigenmodes of such a metallic taper by filtering in the spatial frequency domain. Our approach has the potential to considerably improve the signal-to-background ratio in spectroscopic experiments at the nanoscale.
authors.affiliation: Institut für Physik, Carl von Ossietzky Universität, 26129 Oldenburg, Germany ; Center of Interface Science, Carl von Ossietzky Universität, 26129 Oldenburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Esmann
authors.forename: Simon F
authors.initials: SF
authors.lastname: Becker
authors.forename: Bernard B
authors.initials: BB
authors.lastname: da Cunha
authors.forename: Jens H
authors.initials: JH
authors.lastname: Brauer
authors.forename: Ralf
authors.initials: R
authors.lastname: Vogelgesang
authors.forename: Petra
authors.initials: P
authors.lastname: Groß
authors.forename: Christoph
authors.initials: C
authors.lastname: Lienau
keywords: Fourier optics; adiabatic nanofocusing; metallic wire modes; plasmonics; scanning near-field optical microscopy (SNOM)