Lichtmikroskopie mit Doughnut-Moden: ein Konzept zur Detektion, Charakterisierung und Manipulation einzelner Nanoobjekte

Relative spectral tuning of the vertical versus base modes in plasmonic nanocones

Gold nanocones acting as optical antennas offer an excellent geometry for focusing light near the cone tip, acting as nano-light sources with spot sizes on the order of the tip radius. However only the vertical plasmon mode oscillating in the axial direction can effectively excite the tip, whereas lateral modes oscillating along the cone base create mostly unwanted background in applications. The present work investigates the three-dimensional plasmonic mode structure of nanocones both experimentally and numerically. By tuning the nanocone aspect ratio, the modes can be spectrally tuned relative to each other, making them coincide for maximum excitation, or tuning the base mode away from the vertical mode for effective background suppression.

Au nanotip as luminescent near-field probe

We introduce a new optical near-field mapping method, namely utilizing the plasmon-mediated luminescence from the apex of a sharp gold nanotip. The tip acts as a quasi-point light source which does not suffer from bleaching and gives a spatial resolution of ≤25 nm. We demonstrate our method by imaging the near field of azimuthally and radially polarized plasmonic modes of nonluminescent aluminum oligomers.