A multilayer surface plasmon resonance system was designed for high-precision chemical sensor applications. In this sensor, the angular distribution of reflectance from a thin metal film—which is in contact with a sample—is measured. An absorption peak is observed whose angular distribution of reflectance, owing to the excitation of surface plasmon resonance, is measured. The refractive index of the sample is determined from this peak angle. The resolution limit for refractive-index measurements is determined by the absorption peak width. We describe a multilayer system in which an additional layer is added to the conventional Kretschmann geometry; as a result, peak widths are significantly reduced. The angular distribution of reflectance is calculated using Fresnel's formulas and multiple-reflectance theory in order to understand the effect of thickness and refractive index of the additional layer. By optimizing the thickness of the layer, peak widths are reduced to approximately one third of that obtained using the Kretschmann geometry. Experimental results demonstrate the feasibility of this approach.
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