Resonance enhancement effects in Raman-enhancing pyramid-like V-shape groove microstructures

TL;DR

This paper demonstrates that pyramid-like V-shape groove microstructures can significantly enhance Raman signals through resonance effects caused by diffraction and near-field interference, independent of surface plasmons.

Contribution

The study provides a theoretical analysis showing resonance enhancement in simplified 2D geometries without plasmon effects, highlighting the role of diffraction and near-field interference.

Findings

Resonance effects cause significant local intensity increases.

Near-field diffraction patterns are key to the enhancement.

Raman signal can be amplified without plasmon involvement.

Abstract

Microscopic pyramidal pits in a reflective surface, a geometry similar to a retroreflector, are frequently used to enhance signal strength. The enhancement effect is generally attributed to surface plasmons, however, the sub-wavelength to near-wavelength dimensions of the pyramidal 3D geometry suggest contributions from diffraction and near-field effects. Our theoretical analysis of the light intensity distribution in the similar (but simpler) 2D geometry assuming a perfect conductor screen, that is, in the absence of any plasmon effects, shows that interference patterns forming within the cavity cause a significant resonant increase in local intensity. Such effect can be important for many applications, especially for the widely used Raman spectroscopy. Resonant enhancement without plasmons of the emitted Raman signal due to enhanced local field amplitude is also possible, which implies that the geometry practically implements a Raman laser. Comparison of diffraction patterns obtained with near-field and far-field approaches reveals that the near-field component is responsible for the observed dramatic intensity enhancement, and thus the Raman enhancement as well.