Martin L. Kurth

Gap Surface Plasmon Waveguides with Enhanced Integration and Functionality

We propose and investigate theoretically and experimentally L-shaped gap surface plasmon waveguides (L-GSPWs) formed by a dielectric film (strip) partially enclosed between two metal films. The proposed L-GSPWs combine the benefits of strong plasmon localization in a nanogap, significant propagation distance, low cross-talk between two neighboring waveguides, high transmission through a sharp 90° bend, and simplicity of fabrication by means of the standard lithography combined with the thin film deposition.

Plasmon Nanofocusing with Negative Refraction in a High-Index Dielectric Wedge

Here, we describe a metal-insulator-insulator nanofocusing structure formed by a high-permittivity dielectric wedge on a metal substrate. The structure is shown to produce nanofocusing of surface plasmon polaritons (SPPs) in the direction opposite to the taper of the wedge, including a range of nanoplasmonic effects such as nanofocusing of SPPs with negative refraction, formation of plasmonic caustics within a nanoscale distance from the wedge tip, mutual transformation of SPP modes, and significant local field enhancements in the adiabatic and strongly nonadiabatic regimes. A combination of approximate analytical and rigorous numerical approaches is used to analyze the strength and position of caustics in the structure. In particular, it is demonstrated that strong SPP localization within spatial regions as small as a few tens of nanometers near the caustic is achievable in the considered structures. Contrary to other nanofocusing configurations, efficient nanofocusing is shown to occur in the strongly nonadiabatic regime with taper angles of the dielectric wedge as large as ∼40° and within uniquely short distances (as small as a few dozens of nanometers) from the tip of the wedge. Physical interpretations of the obtained results are also presented and discussed.

The plasmonic Raman sensor using periodic nanofocusing arrays

A novel plasmonic Raman sensor using periodic nano-hole and, potentially, nanofocusing arrays is investigated numerically and experimentally. The effect of structural parameters (such as periodicity of the structure, hole dimensions, etc.) is determined and investigated. The analysed structures are fabricated in thin gold films by means of focused ion beam lithography. Optical characteristics of the fabricated arrays are determined experimentally and compared with the theoretical predictions. Experimental field enhancements are determined and also compared with the theoretical predictions.

Fabrication of Holographic Gratings in Photosensitive Media With a Passively Stable Sagnac Optical Arrangement

A novel passive arrangement based on a Sagnac interferometer is described that produces interference patterns more stable than those produced by a conventional arrangement. An analysis of the structure is presented that shows it to be an order of magnitude more stable than an equivalent conventional approach. The excellent fringe stability allowed holographic gratings with small periods (~0.5 µm) to be written in photorefractive lithium niobate with low intensity writing fields (~mW cm−2), despite long grating fabrication times (~1000 s). This was possible because the optical arrangement compensated for phase shifts introduced by translational and rotational mirror motion caused by environmental perturbations.