Fabrication, linear and nonlinear spectroscopy of optical nano-antennas and hybrid antenna-systems

Plasmonic nanostructures that act as optical nanoantennas for visible light offer interesting opportunities for locally concentrating and enhancing the electric near-field of an incident light wave, or of spectrally tuning the antenna characteristics via the size, shape and material.
These properties are increasingly employed for the development of high-resolution optical mi-croscopy and nanospectroscopy. Using various nanofabrication techniques, suitable antenna structures can be prepared for surface-enhanced Raman spectroscopy (SERS), optical near-field scanning probes, or nano-optical (bio-)sensors. By combining the antenna structures with a second component in hybrid configurations, such as quantum dots, fluorescent molecules, or organic thin-films, the antennas can be employed to modify the absorption and emission char-acteristics of these objects in the coupled system. Key challenges in this context are the opti-mization of the antenna properties in view of the envisaged application, as well as achieving selective coupling of the nano-emitters to the high near-field regions of individual antennas.
In this presentation the top-down nanofabrication of different optical antennas by various nano-lithographic techniques, combined with etch-mask transfer, will be demonstrated. Their linear and nonlinear optical properties are investigated. Conical nanoantennas offer narrow, high near-field intensity hotspots near their tip apexes. Different procedures for selectively coupling few or single nano-emitters to these tips will be shown. Applications of different hy-brid antenna configurations for absorption enhancement in organic thin films, emission en-hancement and lifetime reduction of single quantum dots coupled to nanocones, and biosens-ing through plasmon resonance shifts after integration in a microfluidic environment will be illustrated.