Radiative pumping vs vibrational relaxation of molecular polaritons: a bosonic mapping approach

TL;DR

This paper introduces a bosonic formalism to analyze molecular polaritons, deriving rates for radiative pumping and vibrational relaxation, revealing finite N effects and a new polariton-assisted Raman scattering process.

Contribution

The formalism accommodates arbitrary molecules and vibronic structures, providing a rigorous derivation of relaxation rates and identifying a novel Raman scattering mechanism.

Findings

Radiative pumping rate divided into transmitted and re-absorbed components.

Vibrational relaxation includes a finite N correction and a second-order Raman process.

Enhanced Raman scattering occurs when fluorescence and polariton frequencies match.

Abstract

We present a formalism to study molecular polaritons based on the bosonization of molecular vibronic states. This formalism accommodates an arbitrary number of molecules $N$, excitations and internal vibronic structures, making it ideal for investigating molecular polariton processes accounting for finite $N$ effects. We employ this formalism to rigorously derive radiative pumping and vibrational relaxation rates. We show that radiative pumping is the emission from incoherent excitons and divide its rate into transmitted and re-absorbed components. On the other hand, the vibrational relaxation rate in the weak linear vibronic coupling regime is composed of a $\mathcal{O}(1/N)$ contribution already accounted for by radiative pumping, and a $\mathcal{O}(1/N^2)$ contribution from a second-order process in the \textit{single}-molecule light-matter coupling that we call polariton-assisted Raman scattering. This scattering is enhanced when the difference between fluorescence and lower polariton frequencies matches a Raman-active excitation.