k-space imaging of the eigenmodes of sharp gold tapers for scanning near-field optical microscopy

• Martin Esmann,
• Simon F. Becker,
• Bernard B. da Cunha,
• Jens H. Brauer,
• Ralf Vogelgesang,
• Petra Groß and
• Christoph Lienau

Beilstein J. Nanotechnol. 2013, 4, 603–610, doi:10.3762/bjnano.4.67

• 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

• frequency domain. Our approach has the potential to considerably improve the signal-to-background ratio in spectroscopic experiments at the nanoscale. Keywords: adiabatic nanofocusing; Fourier optics; metallic wire modes; plasmonics; scanning near-field optical microscopy (SNOM); Introduction Metallic

• opening angle [6]. This formation of a strongly confined lightspot is now termed “adiabatic nanofocusing” [6]. The expected nanometer-scale confinement offers the possibility to efficiently couple light into a single nanoobject, making such probes highly attractive for inherently background-free, new