THE INTERACTION BETWEEN ELECTRIC DIPOLES AND WAVEGUIDING SURFACES AT OPTICAL FREQUENCIES (SURFACE PLASMONS, SILVER ISLANDS, WAVEGUIDES, ENHANCEMENT)

An electric dipole placed in close proximity to a surface exhibits optical properties that are very different from those of an isolated electric dipole. In the case of a conducting surface, classical theory predicts that the dipole will exhibit a resonance frequency shift, a change in its radiative decay rate, and coupling with a transverse magnetic surface wave at the metal-air interface (i.e. a surface plasmon). These effects have been observed, measured, and analyzed on a dipole/surface system which incorporates a high index dielectric layer between the dipole and the metal, thus forming a metal-clad waveguiding structure.;Fluorescence measurements with dye molecules deposited on the same waveguiding structure show that the radiative intensity can be enhanced by more than two orders of magnitude. This large increase in the radiative yield has been attributed to the occurrence of higher order waveguide modes which interact with the molecules, and the major features of the results agree well with a classical theory.;The results show that sub-wavelength size metal particles with macroscopic dipole moments, when used in this experimental geometry, will exhibit significant resonance frequency shifts. The interaction between these macroscopic dipoles and the propagating surface plasmon resonance also induces a shift in the dispersion relation (omega) (k) which displays the characteristic energy-momentum states of the surface resonance. Measurements of the radiative decay of surface plasmons through a prism show that this interaction leads to a strong coupling which enhances the transfer of energy into the waveguide.