Theoretical modeling of a nanoplasmonic-whispering-gallery-mode hybrid microresonator for estimating enhancement of single-molecule Raman scattering and fluorescence

We propose a high-quality-factor nanoplasmonic-whispering-gallery-mode (WGM) hybrid microresonator (HMR) for the enhancement of a single-molecule Raman scattering signal. Using the reactive sensing principle, we have analytically developed a working formula for estimating the enhancement factor (eta) that depends on the quality factor of the WGM as well as on the power and wavelength of incident light. The simulations, carried out using developed theory, revealed that the enhancement due to the HMR is at least 1-3 orders higher relative to the conventional surface-enhanced Raman scattering technique. The HMR efficiency for obtaining a higher value of eta was found to depend on efficient evanescent coupling of laser light into the HMR. The proposed HMR was also found suitable in enhancing single-molecule fluorescence. Finally, suitable nanoplasmonic structures have been proposed for making efficient HMRs for studying single-molecule Raman scattering/fluorescence, and their local field strengths have been estimated using the finite element method. (C) 2019 Optical Society of America