Quasi-static analysis of controllable optical cross-sections of a layered nanoparticle with a sandwiched gain layer

We theoretically study the optical performance of a layered nanoparticle with a sandwiched gain shell. Based on quasi-static analysis and full-wave numerical simulations, we show that it is possible to achieve a very high scattering cross-section (over 4 orders) accompanied with a negative absorption cross-section by changing the amount of gain in the sandwiched shell layer. This suggests that the proposed configuration can either be used for designing a spaser or as a switchable nano scatterer whose scattering cross-section can be manipulated from an ultra-high value to an ultra-low one. To provide more insight into the operation of this proposed configuration, we also study the near field, which again confirms a clear controllability of field enhancement through the sandwiched gain layer.