Raman scattering with strongly coupled vibron-polaritons

TL;DR

This paper provides a theoretical analysis of how strong photon-vibron coupling in microcavities enhances Raman scattering in organic molecules, predicting signal division and amplitude enhancement in the ultra-strong coupling regime.

Contribution

It derives compact analytic formulas for Raman scattering under strong coupling for any number of molecules, including the ultra-strong regime, extending previous numerical studies.

Findings

Raman signal splits into upper and lower polariton modes.

Lower polariton Raman amplitude is enhanced due to mode softening.

Theoretical predictions applicable to large molecular ensembles.

Abstract

Strong coupling between cavity photons and molecular vibrations can lead to the formation of vibron-polaritons. In a recent experiment with PVAc molecules in a metal-metal microcavity [A.Shalabney et al., Ang.Chem.Int.Ed. 54 7971 (2015)], such a coupling was observed to enhance the Raman scattering probability by several orders of magnitude. Inspired by this, we theoretically analyze the effect of strong photon-vibron coupling on the Raman scattering amplitude of organic molecules. This problem has recently been addressed in [J.del Pino, J.Feist and F.J.Garcia-Vidal; J.Phys.Chem.C 119 29132 (2015)] using exact numerics for a small number of molecules. In this paper we derive compact analytic results for any number of molecules, also including the ultra-strong coupling regime. Our calculations predict a division of the Raman signal into upper and lower polariton modes,with some enhancement to the lower polariton Raman amplitude due to the mode softening under strong coupling.