Phase and amplitude detection of surface plasmon polariton coupling: Theory and experiments.

摘要

This work details the theory and supporting experiments for determination of the sensitivity/signal-to-noise ratio of the surface plasmon resonance system to external perturbations. Plasmons are a photon-electron coupling in a coherent longitudinally polarized propagating wave. This work is specifically concerned with those waves that are bound to the interface between two different media. The field propagates in a direction parallel to the interface and is evanescent in directions perpendicular to the surface.;The plasmon excitation technique couples optical photons to the electron wave through an evanescent field. This method increases the momentum of the photon to the necessary level required by the allowed modes of propagation while maintaining the appropriate boundary conditions. A prism is used to create the evanescent field by positioning the incident laser beam at an angle greater than that required for total internal reflection. The degree of photon-electron coupling is determined by monitoring the changes of the reflected field.;A new class of sensors have recently been developed exploiting the surface plasmon resonance phenomenon. Typically, these sensors detect environmental perturbation of the complex dielectric constant of the boundary medium or changes in the dielectric constant of the plasmon supporting film itself. These dielectric constant changes result in deviations in the degree of photon-electron resonance coupling. In typical measurements, the deviations manifest themselves in the monitored amplitude of the reflected field as changes in amplitude, resonance minimum and width of the resonance curve at the half power point.;While the use of the plasmon resonance as a sensor has become increasingly common, the measurement techniques and systems presented in the literature have not addressed the issue of sensitivity. Most systems track the extremely insensitive point of the reflected field minimum to determine the sensed quantity. Additionally, the more sensitive phase measurement is exclusive to measurements that are inherently phase measurements.;In this work we present the theoretical and supporting experimental results for the measurement sensitivity of a surface plasmon resonance system in the evanescent field prism coupled configuration. Results are presented for both the phase and amplitude measurements with comparisons between the two types of measurements.