Effect of Dipole-Dipole Interactions on Stimulated Raman Scattering in Plasmonic Nanohybrids

We have developed a theory of the stimulated Raman scattering (SRS) for plasmonic nanohybrids. The nanohybrids are made of an ensemble of interacting metallic nanoshells (MNSs) and quantum dots. The surface plasmon polariton (SPP) field for the MNSs is calculated at the interface between the metallic core and the dielectric shell. An external laser field induces dipoles in MNSs, and dipoles interact with each other via dipole-dipole interactions (DDIs). It is found that the SRS depends on the third-order susceptibility of the plasmonic nanohybrid. The coupled-mode formulism based on Maxwell's equation and the quantum mechanical density matrix method are used to obtain an analytical expression of the Raman gain coefficient (RGC) and SRS intensity. These analytical expressions can be useful for experimental scientists and engineers who can use them to compare their experiments and make new types of plasmonic devices. Further, we found that there is an enhancement in the RGC and SRS intensity. The enhancement is due to the SPPs and DDIs. We have also investigated the effect of geometrical parameters such as the size of the nanoshell on the SRS intensity. Finally, the present theory is applied to explain the existing SRS experiments, and good agreement was found between theory and experiments. Our findings can be used to fabricate optical nano-amplifiers and nanosensors in the regime around the Raman Stokes field frequency.