Surface Plasmons as Interfacial Light

It should be pointed out that both, the reflectivity curve R(0), as well as, the angular distribution of the optical field intensity Is(9) are described by Fresnel s equations, i.e., can be calculated based on Maxwell s theory of such a layered architecture. Once R(6) is calculated by using the dielectric functions and the thicknesses of the involved materials (prism, metal layer, functional interfacial binding matrix, dielectric superstrate) the optical intensity and its angular dependence ls(0) can be calculated without any additional free parameter. It is important to keep in mind that for fluorescence spectroscopy with surface plasmon excitation it is the optical intensity Ij (and its angular dependence) that controls the excitation process of the fluorophores. 

The decay is much faster into the Au metal owing to the screening effect of the nearly free electron gas. Relevant for our spectroscopic purposes, however, is only the evanescent character of the surface mode, which leads to an extension of the optical field into the aqueous phase of about 150 nm (defined by the 1/e decay of the peak intensity). This means that only chromophores that are within this exponential decay of the excitation light will be reached for fluorescence excitation and emission. However, this field then will be much stronger than that of the in-coupling laser beam. 

As has been discussed in great detail, the grating effectively imposes a Brillouin Zone structure upon the surface plasmon dispersion, resulting in various dispersion 

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