Surface enhanced Raman scattering in the presence of multilayer dielectric structures
Spotlight summary: Since its discovery in 1974, surface enhanced Raman scattering (SERS) has become a promising spectroscopic technology for molecular identification due to its high sensitivity and molecular specificity, with applications spanning environmental control, food safety, medical, and security concerns. While SERS is generally considered as a process in which the Raman signal is significantly enhanced by the surface plasmon resonance of the metallic nanostructures, much less attention has been paid to fully dielectric structures by the SERS community. However, fully dielectric structures can also enhance Raman scattering by field enhancement provided by confined modes near the positions of adsorbed molecules. In fact, the great advantage of these structures is that they do not suffer from the high absorption losses present in the conventional metallic nanostructures.
In this paper, Delfan et al. introduce a systematic and semi-classical model that allows the study of SERS in an arbitrary multilayer planar structure. The authors provide analytical expressions of the Raman cross sections for scattering into both the cladding and substrate in terms of the Fresnel coefficients of the structure and predict large enhancement factors in fully dielectric structures. This is, to our knowledge, the first time such in-depth analysis has been carried out to target the SERS application of fully dielectric structures.
The sensing platform used in this study is the Kretschmann configuration. Compared to the previous work utilizing the Otto configuration, this configuration allows the detection of the Raman signal through a prism substrate, which not only reduces the interaction of the scattered field with the solution containing the analyte, but also leads to an additional enhancement for the radiation power if the scattered field can be coupled to guided modes of the planar structure.
Numerical calculations for three examples were provided by Delfan et al.: the Bloch surface wave structure, the waveguide structure, and the conventional surface plasmon structure. A maximum enhancement factor of about 10^6 was found for excitation of a Bloch surface wave structure at 532 nm, which is much larger than that in the Otto configuration and comparable to the typical value in metal nanostructures.
The results of this paper are quite valuable as they provide a fundamental model for fully dielectric-based SERS sensing strategies. For what regards the future work, it would be interesting to see experimental demonstrations of these structures as SERS substrates; a combination of this platform and conventional metal nanostructures will likely further enhance the sensitivity. The authors also predict that Bloch surface wave structures could be a promising platform for coherent anti-Stokes Raman scattering and multiplexed sensing. Therefore, this paper will be of great interest to researchers in both the plasmonics/SERS community and the dielectric/waveguide structures community.
--Xuan Yang and Claire Gu
Technical Division: Light–Matter Interactions
ToC Category: Optics at Surfaces
|OCIS Codes:||(240.6690) Optics at surfaces : Surface waves|
|(310.2785) Thin films : Guided wave applications|
|(280.4788) Remote sensing and sensors : Optical sensing and sensors|
|(240.6695) Optics at surfaces : Surface-enhanced Raman scattering|
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