Surface Plasmon Polariton Nano-Optics

The ongoing miniaturization in todays cutting edge technology has triggered the emergence of nanotechnology. Within this field intense research effort in, e.g., material science, chemistry, electronics or microscopy is conducted, often combined to interdisciplinary research. When it comes to optics, however, we find the nanoscale to be out of reach for conventional optics: diffraction limits the spatial resolution to a value given by about half the light wavelength. To overcome this limitation is of great interest for both basic research and technological applications. The investigation of the wealth of optical phenomena by the broad range of readily available radiation sources and detection devices would clearly profit from an extension of the spatial resolution beyond the diffraction limit. Furthermore such an extension would open up the way to a further miniaturization of integrated optical devices. Since the beginning of the 1990`s new routes towards the control of light wave propagation at the micro and nano-scale are explored. Relying on dielectric structures, photonic band gap materials and high dielectric contrast materials have been explored. For the latter a strong light field confinement permits to reduce the cross section of the waveguides and to decrease radiative losses in bends. Recent results have demonstrated that visible light from an evanescent local source can be efficiently propagated through a waveguide only 200 nm wide. Besides dielectric materials, metals have been investigated for their potential in downsizing optics beyond the diffraction limit. Recently surface plasmon polaritons (SPPs) excited in metal nanostructures were identified as promising candidates to serve that need. SPPs are resonant electromagnetic surface modes constituted by a light field coupled to a collective oscillation of conduction electrons at the interface of a metal and a dielectric. The corresponding electromagnetic fields are strongly localized at the interface. If the interface is formed by a nanostructure, it is the spatial dimension of the nanostructure rather than the light wavelength that determines the spatial extension of the SPP field, thus rendering optics beyond the diffraction limit possible. The practical aim of this project is the experimental realization and optimization of mirrors, beamsplitters and interferometers for propagating SPPs. Together with the local launch of a directed SPP via a metal nanostructure, these two elements will allow the realization of a SPP interferometer. Furthermore, the feasibility of a SPP based spectral filter will be investigated. Additionally, the task of project is a detail understanding of how the nanoparticles and -structures that make these SPP optical elements interact with the propagating plasmons, i.e., what is the role of their geometries, resonance frequencies and so on.