Scouting for strong light–matter coupling signatures in Raman spectra

Abstract

Changes in the Raman spectra under vibrational strong coupling do not necessarily result from the coupling effect but rather they can be caused by the surface enhancement effect.

Chemistry under Vibrational Strong Coupling

“…52,120,121 It is important to note that the enhancement of modified Raman scattering under VSC reported in ref 52 most likely includes a contribution from a surface-enhanced Raman spectroscopy (SERS) effect, in agreement with a more recent study. 122 We have found that the Raman laser, even at low power, can lead to a modification of the top mirror surface, particularly in the case of polymer-based cavities, so great care must be taken when interpreting Raman spectra on such samples, as they most probably reflect different superimposed phenomena.…”

“…Hybrid polaritonic states, formed under ESC, have proven to show modified excited-state properties of the materials, such as distance-independent long-range energy transfer between the molecules due to their entangled and delocalized nature. , Similarly, VSC also alters light-induced/excited-state processes such as vibrational energy transfer . Pump–probe experiments on polaritonic states under VSC reveal the vibrational dynamics of the coupled system and raise further questions about the consequences of VSC on molecular properties. ,, Raman scattering has been reported to be enhanced under both ESC and VSC. ,, It is important to note that the enhancement of modified Raman scattering under VSC reported in ref most likely includes a contribution from a surface-enhanced Raman spectroscopy (SERS) effect, in agreement with a more recent study . We have found that the Raman laser, even at low power, can lead to a modification of the top mirror surface, particularly in the case of polymer-based cavities, so great care must be taken when interpreting Raman spectra on such samples, as they most probably reflect different superimposed phenomena.…”

Chasing Vibro-Polariton Fingerprints in Infrared and Raman Spectra Using Surface Lattice Resonances on Extended Metasurfaces

“… 37 , 42 However, other studies have not found clear signatures of strong coupling in the Raman signal despite showing strong coupling in the IR spectra. 38 In contrast, theoretical works suggest that the Rabi splitting of a strongly coupled system should be present in the Raman spectra, with the lower and upper polariton located at the same energies and with the same linewidth as in the IR spectra. 42 , 43 Motivated by these contradicting results, we have investigated the presence of polaritons in the Raman spectra of the strongly coupled molecules to SLRs.…”

“…The absence of polaritons in the Raman spectra and micro-Raman maps, even in regions with high SLR field enhancement, confirms previous results in Fabry–Perot cavities. 38 , 49 A possible explanation for this absence could be found in the less-than-ideal spatial overlap of the electromagnetic modes at optical and infrared wavelengths. 42 , 43 , 50 This is a consequence of the inhomogeneity of the field profile in our periodic array, as shown in Figure 2 c–e.…”

“… 37 However, other recent studies do not observe the presence of the polariton bands in Raman spectra and only show a small signal enhancement of the molecular Raman peaks. 38 These contradicting results motivate the investigation of VSC in open systems, such as metasurfaces or arrays of resonant scatterers, where Raman signals can be spatially resolved.…”