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. © 2013 Esmann et al; licensee Beilstein-Institut.
Esmann, M., Becker, S. F., Cunha, B. B. da, Brauer, J. H., Vogelgesang, R., Groß, P., & Lienau, C. (2013). k-space imaging of the eigenmodes of sharp gold tapers for scanning near-field optical microscopy. Beilstein Journal of Nanotechnology, 4(1), 603–610. https://doi.org/10.3762/bjnano.4.67