The Electromagnetic Enhancement of SERS and the Modified Partition of Optical States in the Strong Matter-Coupling Regime.

Surface enhanced Raman Spectroscopy (SERS) is a powerful optical sensing technique that is based on enhanced Raman signals from molecules in proximity of rough metal surfaces. Experiments¹ have shown unexpected large enhancements in SERS, even up to 10¹⁴. Conventional electromagnetic theory accounts for enhancements only up to 10⁶, and the anomalous enhancements have been sometimes attributed to an unknown chemical origin². We highlight the need for a modification to the conventional partition of optical states in the case of an emitter strongly coupled to absorbing matter, and such high gains can be inferred as the result of tunneling out of photons from the strongly absorbing metal surface. This modification to the conventional partition of optical states into its radiative and non-radiative parts, is also imperative for emitters proximal to limiting small metal nanoparticles (< 10 nm in dimensions) which are fully absorbing and do not scatter light^3,4. This effect can be exploited further in light generation, optical sensing and radiative heat transfer.
¹Zeisel, D., et al., Chem. Phys. Letters, 283, 381-385(1998)
²Kneipp, K., J. Phys. Chem. C, 120, 21076(2016)
³Jain, K., & Venkatapathi, M. Phys. Rev. Applied, 11, 054002(2019)
⁴Dutta, R., et al., Phys. Rev. B, 100, 155413(2019)