Giant absorption of light by molecular vibrations on a chip

TL;DR

This paper demonstrates a significant enhancement in molecular vibrational absorption on a chip, driven by a transition from ballistic to diffusive light propagation, with potential implications for molecular sensing.

Contribution

It provides the first experimental evidence of giant absorption enhancement due to diffusive light propagation in a waveguide, highlighting the role of surface modification and molecular nano-layers.

Findings

Absorption enhancement factor of 300 in N-Methylaniline.

Absorption enhancement factor of 80 in Aniline.

Transition from ballistic to diffusive light propagation increases absorption.

Abstract

Vibrational overtone spectroscopy of molecules is a powerful tool for drawing information on molecular structure and dynamics. It relies on absorption of near infrared radiation (NIR) by molecular vibrations. Here we show the experimental evidence of giant enhancement of the absorption of light in solutions of organic molecules due to the switch from ballistic to diffusive propagation of light through a channel silicate glass waveguide. We also experimentally address a dynamics of absorption as a function of time of adsorption of the organic molecules on a waveguide. The observed enhancement in diffusion regime is by a factor of 300 in N-Methylaniline and by factor of 80 in Aniline compared to the expected values in the ballistic propagation of light in a waveguide. Our results underscore the importance of a guide surface modification and the disordered6 molecular nano-layer in enhancement of absorption by amines on engineered integrated system.