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Research

Research Group Nanophotonics

Our research interests are devoted to the investigation of nanophotonic systems. In particular metallic nanostructures provide unique opportunities to manipulate and control light on a sub-wavelength scale. We pursue an active research program in the fields of plasmonics and photonic metamaterials in which we investigate the optical properties of individual metallic nanostructures and artificial optical media, respectively. Brief summaries of current research projects can be found below.


Small is beautiful

Our research group has extensive experience in the design and fabrication of high quality metallic nanostructures for optical applications. Electron beam lithography is our method of choice for production of planar nanostructures with feature sizes down to 50 nm. For the fabrication of 3D nanostructures, we operate a direct laser writing system.

 Fabrication

 

Optical antennas

An antenna is a device that converts the energy of a propagating wave to localized energy and vice versa. The technological progress of the last years in the field of nano-fabrication has paved the way to transfer this concept to the optical domain. Optical antennae fabricated for the near infrared and visible spectral range offer new and exciting possibilities to manipulate and control light, e.g., by focusing beyond the diffraction limit or by directing the emission of quantum emitters.

A key topic of our current research is the coupling of solid-state quantum emitters (semiconductor quantum dots or nanodiamonds with color centers) to metallic or dielectric optical antennas. The basic idea is here that we can use the optical antennas to tailor the electromagnetic environment of the emitters. For instance, we have recently demonstrated the directional emission of colloidal semiconductor quantum dots coupled to dielectric leaky-wave nanoantennas [M. Peter et al., Nano Lett. 17,  4178 (2017)] .

Dielectric optical antenna

 

Plasmonic quantum simulators

Discrete photonic systems such as coupled waveguide arrays can show interesting dynamics that resemble quantum mechanical condensed matter phenomena. The basis for this is the mathematical equivalence between the time dependent Schrödinger equation and the coupled mode equation used to describe the propagation of light in arrays of waveguides. This allows to map the time-dependent probability distribution of an electronic wave packet onto the spatial light intensity distribution in the waveguide array and hence to directly visualize the quantum mechanical evolution in a coherent, yet classical wave environment.

In our experiments, we employ arrays of evanescently coupled dielectric-loaded surface plasmon polariton waveguides (DLSPPWs) as one dimensional plasmonic quantum simulators. Each DLSPPWs consists of a Poly(methyl methacrylate) (PMMA) ridge on top of a thin gold film. The arrays are fabricated with a recently developed negative-tone gray-scale electron beam lithography process. The evolution of the surface plasmon polaritons is monitored by leakage radiation microscopy. 

Plasmonic Bloch Oscillations 

 

Near-field Microscopy: Getting a deeper insight 

Nanostructures offer many new and exciting optical properties which are not available in natural materials. The in-depth understanding of these properties requires the knowledge of the electromagnetic near-field distribution inside the nanostructures.

Electron energy-loss spectroscopy (EELS) in combination with scanning transmission electron microscopy (STEM) is a powerful tool for the spatio-spectral characterization of plasmonic modes on metallic nanostructures. In STEM-EELS, a focused electron beam is raster scanned over the sample and the energy loss of the electrons due to interaction with the sample is recorded for every position of the beam. These EELS-data can be used for spectral imaging of the near-field distribution of photonic metamaterials with nanometer spatial resolution.

This project is carried out in close collaboration with the Electron Microscopy and Analysis (EMA) group at the research center caesar in Bonn.

EELS

 

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