Ultra-sensitive surface absorption spectroscopy using sub-wavelength diameter optical fibers

TL;DR

This paper demonstrates ultra-sensitive surface absorption spectroscopy using sub-wavelength optical fibers, enabling detection of surface particles with significantly enhanced sensitivity compared to traditional methods.

Contribution

The study introduces a novel fiber-based spectroscopy technique leveraging evanescent fields of sub-wavelength fibers for highly sensitive surface detection.

Findings

Detection of sub-monolayers of molecules at ambient conditions

Observation of molecular agglomeration dynamics over seconds to minutes

Absorption sensitivity orders of magnitude higher than conventional methods

Abstract

The guided modes of sub-wavelength diameter air-clad optical fibers exhibit a pronounced evanescent field. The absorption of particles on the fiber surface is therefore readily detected via the fiber transmission. We show that the resulting absorption for a given surface coverage can be orders of magnitude higher than for conventional surface spectroscopy. As a demonstration, we present measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules at ambient conditions, revealing the agglomeration dynamics on a second to minutes timescale.