Signatures of Vibrational Strong Coupling in Raman Scattering

We have analyzed theoretically how the emergence of collective strong coupling between vibrational excitations and confined cavity modes affects Raman scattering processes. This work was motivated by recent experiments (Shalabney et al. Angew. Chem., Int. Ed. 2015, 54, 7971) that reported enhancements of up to 3 orders of magnitude in the Raman signal. By using different models within linear response theory, we show that the total Raman cross section is maintained constant when the system evolves from the weak-coupling limit to the strong-coupling regime. A redistribution of the Raman signal among the two polaritons is the main fingerprint of vibrational strong coupling in the Raman spectrum.