Dispersed and encapsulated gain medium in plasmonic nanoparticles: a multipronged approach to mitigate optical losses.

The performance of all metamaterial-based applications is significantly limited by the inherent and strong energy dissipation present in metals, especially in the visible range. In fact, these materials suffer from rather strong damping of the plasmon fields which can become obstructive for most optical and photonic applications. Therefore, eliminating losses in optical metamaterials is critical for enabling their numerous potential applications. We experimentally demonstrate that the incorporation of gain material (fluorophores) in the high-local-field areas of a metamaterial subunits (gold core/silica shell nanoparticles) makes it possible to induce resonant energy transfer processes from gain units to plasmonic nanoparticles. A comparison between gain-assisted (nanoparticle-dye dispersion) and gain-functionalized (dye encapsulated into the shell) systems is reported. Fluorescence quenching and time-resolved spectroscopy along with modification of Rayleigh scattering and transmission of a probe beam as a function of impinging energy are key evidence of the strong coupling occurring between NPs and gain medium. The multipronged approach used to compensate losses in these metal-based subunits permits one to obtain important advances in materials science and paves the way toward further promising scientific research aimed to enable the wide range of electromagnetic properties of optical metamaterials.