Angular Goos-Hanchen Shift Sensor Using a Gold Film Enhanced by Surface Plasmon Resonance

We demonstrate the surface plasmon resonance (SPR)-enhanced angular Goos-Hanchen (GH) shift. Typical SPR-enhanced GH shift measurements make use of loosely collimated beams, which enhances only the spatial GH shift (Delta(GH)). Unlike this scheme, we focused the incident beam to a small beam waist to induce enhancement in the angular GH shift (Theta(GH)). Although this makes Delta(GH) negligible, the enhancement of Theta(GH) is much larger than the decrease in Delta(GH). In order to excite surface plasmons, we employ a Kretschmann configuration using a simple gold (Au) film on a substrate. We show that although the efficiency of surface plasmon excitation is decreased by the focused geometry, a significantly large Theta(GH) was induced. With the simultaneous measurement of reflectivity for SPR and the beam shift for the GH shift used in this work, we experimentally show the potential of measuring enhanced Theta(GH) toward sensing application when the Au film is exposed to local environmental changes even in the simplest thin film structure.

Automated summary

In this study, surface plasmon resonance (SPR) was used to enhance the angular Goos-Hanchen (GH) shift. By focusing the incident beam to a small beam waist, a significant increase in the angular GH shift was induced, while the spatial GH shift was negligible. Despite decreased efficiency in surface plasmon excitation due to the focused geometry, a large enhancement in the angular GH shift was demonstrated.