Detection of low chemical concentrations by cavity ring-down in an evanescently coupled fused optical fibre taper

Farries, Mark C., Shaw, Andrew M., Fisk, Jonty and Garvey, Liam (2004) Detection of low chemical concentrations by cavity ring-down in an evanescently coupled fused optical fibre taper. In: European Symposium on Optics and Photonics for Defence and Security, 25-28 OCTOBER 2004, London, United Kingdom.

Full content URL: https://doi.org/10.1117/12.578549

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Item Type:Conference or Workshop contribution (Paper)
Item Status:Live Archive

Abstract

A novel sensor for detecting very low concentrations of chemicals in water and other liquids is presented. A cavity ring-down spectrometer has been developed that can measure chemicals in solution in a harsh environment. The high Q Fabry Perot cavity is fabricated in an optical fibre with high reflectivity mirrors on each end. The cavity contains a fused fibre taper, with very low intrinsic loss, for coupling light in the cavity evanescently into a smart surface layer that is bound on to the fibre surface. Small changes in the absorption are detected by changes in the ring-down time of the resonant cavity. The low loss cavity results in ring down times of 1μs for a 2 m cavity, which is equivalent to 100 passes through the smart surface. The ring down time provides a very accurate measure of absorbance because it is independent of source and detector drift and the fibre cavity is unaffected by changes in temperature, vibration or bending. Absorption changes of 5x10-5 dB can be detected with the current configuration and further improvements can be achieved by optimisation leading to detection of atto-molar chemical concentrations.

Keywords:cavity ring-down, e-CRDS, optical fibre, absorption, evanescent
Subjects:F Physical Sciences > F112 Colour Chemistry
F Physical Sciences > F110 Applied Chemistry
F Physical Sciences > F361 Laser Physics
F Physical Sciences > F100 Chemistry
F Physical Sciences > F180 Analytical Chemistry
Divisions:College of Science > School of Geography
ID Code:47607
Deposited On:04 Feb 2022 11:57

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