Nanoscale Plasmonic Slot Waveguides for Enhanced Raman Spectroscopy

TL;DR

This paper presents a theoretical study of nanoscale plasmonic slot waveguides that significantly enhance Raman spectroscopy signals by leveraging electric field enhancements and optimized waveguide designs, enabling more sensitive detection in smaller volumes.

Contribution

The paper introduces an analytical methodology for calculating Raman enhancement in waveguide sensors and compares various plasmonic slot waveguide designs for optimal performance.

Findings

Raman enhancement factors are up to 5.3 times higher than optofluidic fibers.

Integrated plasmonic waveguides reduce device size and analyte volume by over three orders of magnitude.

Optimal waveguide designs maximize Raman signal enhancement.

Abstract

We theoretically investigate several types of plasmonic slot waveguides for enhancing the measured signal in Raman spectroscopy, which is a consequence of electric field and Purcell factor enhancements, as well as an increase in light-matter interaction volume and the Raman signal collection efficiency. An intuitive methodology is presented for calculating the accumulated Raman enhancement factor of an ensemble of molecules in waveguide sensing, which exploits an analytical photon Green function expansion in terms of the waveguide normal modes, and we combine this with a quantum optics formalism of the molecule-waveguide interaction to model Raman scattering. We subsequently show how integrated plasmonic slot waveguides can attain significantly higher Raman enhancement factors: $\sim$5.3$\times$ compared to optofluidic fibers and $\sim$3.7$\times$ compared to planar integrated dielectric waveguides, with a device size and thus analyte volume of at least three-orders of magnitude less. We also provide a comprehensive comparison between the different types of plasmonic slot waveguides based on the important figures-of-merit, and determine the optimal approaches to maximize Raman enhancement.