Multipolar emission in the vicinity of metallic nanostructures

Electromagnetic emission from finite-size multipoles very close to metal surfaces exhibiting plasmon resonances can have profound consequences on the characteristics of the emitted radiation in the far field in both its integrated intensity and its spatial distribution. The problem is relevant for many types of spectroscopies that use metals to enhance optical signals, but it also represents a complementary aspect to the recent interest in near-field imaging via surface plasmon resonances. The breakdown of selection rules for multipolar emission and the phenomenon of radiation funnelling in the far field are explicitly discussed. The relevance of these concepts for certain types of spectroscopy, like surface enhanced Raman scattering (SERS), is also highlighted.