New features of surface plasmon resonance detected by modulation of electromagnetic radiation polarization

摘要

Using a technique based on modulation of electromagnetic radiationudpolarization, we studied the features of surface plasmon resonance in gold nanofilmsuddeposited onto the surface of a totally reflecting prism (fused quartz). The angularudcharacteristics of the polarization difference of squares of the reflectance coefficientudmodules for s- and p-polarized radiation,ud∆ρ =|Rs|² − |Rp|² , were measured (at a wavelengthudλ = 0.63 µm) for metal films whose thickness varied from 0 up to 120 nm.udContrary to the results given by the traditional techniques, the characteristics of ∆ρ peakudunder the resonance condition. As a result, two nonresonance components were found inudthese characteristics. The values and shapes of their angular dependences are determinedudby the coefficients of internal reflection from the metal and insulator that depend on theudfilm thickness. Application of a model with exponential dependence of the refraction andudextinction coefficients on the metal film thickness led to agreement between the resultsudof calculation from the Fresnel formulas and those obtained experimentally. It was foundudthat characteristic parameter of the exponential corresponds to the metal film thicknessudvalue of 11±0.5 nm.