In-water chemical sensing by fiber-optic evanescent waves spectroscopy using mid-infrared quantum cascade lasers

TL;DR

This paper demonstrates a fiber-optic evanescent wave spectroscopy system using mid-infrared quantum cascade lasers for real-time detection of chemicals in water, enhancing safety in drinking water systems.

Contribution

It introduces a novel in-water chemical sensing method utilizing quantum cascade lasers and silver halide fibers, with theoretical sensitivity analysis and experimental validation.

Findings

Effective real-time detection of ethanol in water

Theoretical sensitivity analysis of the sensing system

Successful spectroscopic detection demonstrated

Abstract

The ability of detecting harmful chemicals is an important safety requirement for drinking water systems. An apparatus for in-water chemical sensing based on the absorption of evanescent waves generated by a quantum cascade laser array propagating in a silver halide optical fiber immersed into water is demonstrated. We present a theoretical analysis of the sensitivity of the system and experimentally characterize its real-time response and spectroscopic detection for injection of a sample chemical (ethanol) in a tube containing water.