Enhanced molecular fluorescence mediated by long-range surface polaritons

Abstract

The energy transfer from a fluorescent molecule to surface polaritons supported by a thin metallic slab with flat surfaces is considered in the framework of classical electromagnetic theory. A detailed analysis of molecular power loss is presented for a free-standing slab as well as for the Sarid ATR configuration in which a prism is used to outcouple surface polaritons from the slab. On the basis of this theory, the intensity of the signal in the prism for fluorescence mediated by long-range surface polaritons in a 15 nm thick silver slab can be larger by a factor of ∼ 1130 at the emission wavelength λ = 514.5 nm in comparison with the intensity of the signal obtainable in the absence of the slab and the prism. Also, a rough estimate of possible enhancement in surface enhanced Raman scattering (SERS) is shown to give a corresponding factor of ∼ 9 × 10 5. In comparison with enhancements obtainable in the Kretschmann ATR configuration, where singleinterface surface polaritons are involved, these values are larger by factors of 5.4 (fluorescence) and roughly 29 (SERS).