Direct optical measurement of light coupling into planar waveguide by plasmonic nanoparticles

TL;DR

This study introduces a direct optical method to measure how plasmonic nanoparticles couple light into planar waveguides, revealing the influence of interference, resonances, and illumination direction on coupling efficiency.

Contribution

It provides a novel direct optical measurement technique for light coupling into waveguides by plasmonic nanoparticles, complementing traditional efficiency-based assessments.

Findings

Coupling efficiency is affected by thin-film interference.

Localized surface plasmon resonances influence coupling.

Illumination direction impacts the coupling process.

Abstract

Coupling of light into a thin layer of high refractive index material by plasmonic nanoparticles has been widely studied for application in photovoltaic devices, such as thin-film solar cells. In numerous studies this coupling has been investigated through measurement of e.g. quantum efficiency or photocurrent enhancement. Here we present a direct optical measurement of light coupling into a waveguide by plasmonic nanoparticles. We investigate the coupling efficiency into the guided modes within the waveguide by illuminating the surface of a sample, consisting of a glass slide coated with a high refractive index planar waveguide and plasmonic nanoparticles, while directly measuring the intensity of the light emitted out of the waveguide edge. These experiments were complemented by transmittance and reflectance measurements. We show that the light coupling is strongly affected by thin-film interference, localized surface plasmon resonances of the nanoparticles and the illumination direction (front or rear).