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

Abstract

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