Holger Fischer

Engineering the optical response of plasmonic nanoantennas

The optical properties of plasmonic dipole and bowtie nanoantennas are investigated in detail using the Greens tensor technique. The influence of the geometrical parameters (antenna length, gap dimension and bow angle) on the antenna field enhancement and spectral response is discussed. Dipole and bowtie antennas confine the field in a volume well below the diffraction limit, defined by the gap dimensions. The dipole antenna produces a stronger field enhancement than the bowtie antenna for all investigated antenna geometries. This enhancement can reach three orders of magnitude for the smallest examined gap. Whereas the dipole antenna is monomode in the considered spectral range, the bowtie antenna exhibits multiple resonances. Furthermore, the sensitivity of the antennas to index changes of the environment and of the substrate is investigated in detail for biosensing applications; the bowtie antennas show slightly higher sensitivity than the dipole antenna.

Retardation-induced plasmonic blinking in coupled nanoparticles

We study how retardation leads to interference effects in radiatively coupled plasmonic nanoparticles. We show that inclined illumination through a glass substrate on two plasmonic particles results in either an enhanced field or an attenuated field localized at the position of the first particle. Periodic intensity blinking of the first particle is observed as a function of the particle separation. This phenomenon is nonsymmetric, and almost no blinking is observed on the second particle. The effect is strongest when the illumination angle is chosen such that the optical retardation path in the substrate coincides with the particle distance. Implications of this plasmonic blinking for near-field measurements are discussed.

Characterization of the polarization sensitivity anisotropy of a near-field probe using phase measurements

Amplitude and phase measurements of the near‐field generated by isolated subwavelength apertures in a gold film are presented. The near‐field distribution of such a structure is complex and the measured signal strongly depends on the electric field components effectively detected by the experimental setup. By comparing this signal with 3D vectorial calculations we are able to determine which electric field components are effectively measured. The sensitivity of the phase distribution is key to this measurement. The proposed characterization technique should prove extremely useful to calibrate a Scanning near‐field optical microscopy (SNOM) beforehand in order to retrieve quantitative information on the polarization of the field distribution under study.

Tunable plasmonic nanostructures

We discuss different composite plasmonic nanostructures, which optical properties can be tuned by displacing some of their parts at the nanoscale. The actuation of these structures with MEMs will define new optical functionalities.