Cooperative plasmon-mediated effects and loss compensation by gain dyes near a metal nanoparticle

We present the first unified theory, to the best of our knowledge, of the response of a plasmonic nanosphere (NS) assisted by optical gain media, in the case of a NS coated with a layer of optically active dipolar dyes. We obtain the optical coherent response of the core-shell aggregate in terms of its equivalent polarizability composed of the direct response from the NS and the contribution arising from the cooperative coupling between dyes and surface plasmons of the NS. We identify a mechanism of superradiance-like plasmonic aggregate cooperative emission similar to the conventional Dicke effect with reduced intraband relaxation bandwidth due to the loss compensation in the system. The analysis of the aggregate resonances based on the system eigenvalues provides physical insight into the total loss compensation mechanism and resonance frequency shifts. (C) 2015 Optical Society of America