Azimuthal dependence of electromagnetically induced grating in a double V-type atomic system near a plasmonic nanostructure

We conduct theoretical and numerical studies of the performance of a 2D electromagnetically induced grating in a 4-level quantum system, which is situated near a plasmonic nanostucture. The plasmonic nanostructure is built by metal-coated dielectric nanospheres in a periodic 2D arrangement. The double V-type system is coupled by a weak probe laser, a spatially-dependent standing wave field and a Laguerre–Gaussian field. The plasmonic metamaterial causes quantum interference in the spontaneous emission from the two closely situated upper states, which makes the amplitude and phase modulations of the weak probe light dependent on the azimuthal angle and the orbital angular momentum of the vortex coupling beam. In the absence of the plasmonic nanostructure this behavior does not exist due to the lack of quantum interference. We demonstrate that by adjusting the parameters of the vortex beam, as well as the distance to the plasmonic nanostructure, the amplitude and phase modulations of the probe laser, and the Fraunhofer diffraction patterns of the grating can be controlled, directing the weak probe light energy to high-orders. The spatially dependent coupling light causes the Fraunhofer diffraction to have an asymmetric patterns when a negative or a positive value of the winding number is applied. Our work proposes a straightforward scheme for manipulation of the diffraction efficiency of the grating by utilizing both the winding number of the Laguerre–Gaussian beam, and the distance between the quantum system and the plasmonic nanostructure as control knobs.