Gain-driven singular resonances in active core-shell and nano-shell plasmonic particles

Within the frame of a simple, long-wavelength, quasi-static description, we present theoretical characterization optical response metal nanoparticles doped with active gain elements in core-shell (metallic core within an dielectric shell) and nano-shell (active metallic configurations. The common feature these structures is that, adding to system produces increase quality plasmon resonance, which becomes sharper until singular point, after which, switches from absorptive emissive (nanolaser). We use this aforementioned simple model develop general method allowing us calculate both expected frequency level needed realize it discuss spectral deformation occurring before point. Finally, propose way if behavior reachable using realistic amounts gain.