Control of the absorption of a four-level quantum system near a plasmonic nanostructure

We study the optical response of a four-level double-V-type quantum system which interacts simultaneously with probe and pump laser fields and is located near a two-dimensional array of metal-coated dielectric nanospheres. By considering different coupling configurations for the pump/probe laser fields and analyzing the resulting probe absorption spectrum we reveal a variety of phenomena, such as huge enhancement of the absorption at the central line, gain without inversion, and a phase-dependent absorption spectrum. We also show that the enhancement of probe absorption or the gain can be controlled by varying the distance of the quantum system from the plasmonic nanostructure, the intensity of the pump field(s), and, when applicable, their relative phase. Our results can find applications in on-chip nanoscale photonic devices.