Theoretical investigation on the strong coupling between a molecule and a metallic nanosphere clad with a gain medium

Strong coupling between a molecule and a metallic nanosphere clad by a layer of gain medium, which provides compensation for losses in the metal, is investigated theoretically. We self-consistently solve the classical model of a molecule which is described as a damped oscillating dipole, driven by the field reflected back from the metallic surface. It is found that in a broad range of gain level, the frequencies of this coupled system exhibit a splitting substantially larger than the associated damping rate, a signature of strong coupling. As the gain–dissipation balance is optimized, strong coupling occurs even if the molecule is separated from the nanoparticle by a distance as large as several tens of nanometers. Thus through the aid of a gain medium, experimental observation of strong coupling can be easily achieved. (paper)