Pupil function engineering for surface plasmon microscopic interferometry

Abstract

Interferometric surface plasmon microscopy (SPM) measures plasmonic properties of nano-materials using the so-called V(z) curves. However, experimentally acquired V(z) curves suffer from extremely poor magnitude of interference signals, severe disturbing oscillations and background noises, which show difficulties in practical applications and could not be properly explained by the conventionally ray-model-based principle. The situation is more severe when operating confocal surface plasmon interferometry. This work revisits the conventional principle of interferometric SPM and investigates the fundamental reasons that cause the disagreements between expected V(z) effect and actually acquired V(z) curves. A modified ray model is presented to properly interpret the principle of confocal SPM. We demonstrate how the pupil function engineering can effectively suppress both the systematically disturbing oscillations and severe background noises. The experimental setup is established. Experimental verification and related analysis are also demonstrated.