Causality of surface plasmon polariton emission processes

Fundamental physical quantum phenomena, such as surface plasmon polaritons (SPP's), require specific conditions as described in their dispersion relation for excitation by photons. These conditions exactly define the k vector of the incident photons as well as the elastically reemitted, outbound photons that follow from the decay of the plasmon. Our conclusion demonstrates that these requisites are indeed fulfilled even on the introduction of an inelastic, wavelength-shifting process like fluorescence emission to the system. Such a process is established by placing fluorescent molecules into the strong evanescent field of the SPP. The analysis of the outbound photons shows an angular behavior, which can only be explained if the fluorescent photons also satisfy SPP conditions. This behavior enables the development of a model for the chronology and causality of surface plasmon polariton deexcitation mechanisms.