Optomechanical effects in nanocavity-enhanced resonant Raman scattering of a single molecule

In this paper, we address the optomechanical effects in surface-enhanced resonant Raman scattering (SERRS) from a single molecule in a nanoparticle on mirror (NPoM) nanocavity by developing a quantum master-equation theory, which combines macroscopic quantum electrodynamics and electron-vibration interaction within the framework of open quantum system theory. We supplement the theory with electromagnetic simulations and time-dependent density functional theory calculations in order to study the SERRS of a methylene blue molecule in a realistic NPoM nanocavity. The simulations allow us not only to identify the conditions to achieve conventional optomechanical effects, such as vibrational pumping, nonlinear scaling of Stokes and anti-Stokes scattering, but also to discovery distinct behaviors, such as the saturation of exciton population, the emergence of Mollow triplet side bands, and higher-order Raman scattering. All in all, our study might guide further investigations of optomechanical effects in resonant Raman scattering.