Fluorescence spectrum and time-dependent population of a quantum three-level atom (Strontium) coupled with a silver nano sphere through a silver thin-film

• Several peaks are observed in the spectrum of a three-level atom near the nanostructures.
• The full system shows enhancement of the fluorescence compared to the film+atom structure.
• Population increase is observed by an increase of the film and nano sphere distance in the full system.
• Adding a nano sphere to the other side of the thin film decreases the decay rate and enhances the fluorescence.

The fluorescence spectrum of a Λ type three level atom (Strontium) coupled with a silver nanosphere through a silver thin film, has been determined. This work is based on the Green tensor method and the spectrum for the case of film–atom is compared with the nano structure of thin film–atom–nanosphere (full system). Indeed we see increasing the distance between film and nano sphere and hence by decreasing of the decay rate leads to an increasing of the fluorescence for the full system. Also the time-dependent population of the levels for this atom for recognized cases (film–atom and full system) has been determined. As a consequence we found that in the full system the fluctuation of the population is seen more than the film–atom structure. Also the peaks are larger than in the second case.