Properties of SPCE with Reverse Kretschmann Excitation

Properties of SPCE with Reverse Kretschmann Excitation 

B) of the sample. The intensity observed on the front (F) side of the sample was much lower and not sharply distributed at any particular angle. T o determine the relative intensities of the coupled and free-space emissions, we integrated the intensities observed at all angles on the front side (180° 90°) and the back side (0° 90°). The total back-to-front intensity ratio (Ib 

We considered the possibility that the strong emission near 47° was due to scattered light or a reflection. We proceeded to measwe the emission spectra of the directional SPCE at 47° 

The polarization of the directional emission proves that it is due to coupling with the surface plasmons and that the polarization of the SPCE is independent of the polarization of the normal incidence excitation. Similarly, SPCE is also p-polarized, suggesting that the emission dipoles perpendicular to the plane of incidence do not result in SPCE or at least display less efficient coupling. For accuracy we note that the relationship between fluorophore orientation and coupling to the metal surface has been studied theoretically (as summarized in [27]), but not experimentally. Additionally, we refer to the fluorophore as emitting into the substrate, but one can also consider the surface plasmons to be the source of emission into the substrate. 

In previous studies of the effects of silver particles on fluorophores we observed substantial decreases in lifetime as the intensities increased [6-8]. We interpreted this effect as an increase in the radiative decay rates near the metal particles [32-33]. In an analogous way we expected the radiative decay rate to be increased in the direction of the surface plasmon angle. Stated alternatively, we imagined that a large fraction of the emission appeared as SPCE because the rate of transfer to the surface plasmon was larger than the rate of spontaneous free-space emission. Hence, we expected the lifetime of SPCE to be shorter than the free space emission. 

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