Modifying free-space spontaneous emission near a plasmonic nanostructure

We study theoretically the effects of the presence of a plasmonic nanostructure on free-space spontaneous emission in a four-level quantum system, where one V-type transition is influenced by the interaction with surface plasmons and the other V-type transition occurs in free space. The plasmonic nanostructure that we consider is a two-dimensional array of metal-coated dielectric nanospheres. We show that the spectrum of spontaneous emission in the free-space modes is strongly influenced by the presence of the plasmonic nanostructure, and we explore the dependence of the spectrum on different initial conditions of the quantum system and on the distance from the nanostructure.