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Proceedings Paper

Fiber optic based chemical sensor system for in-situ process measurements using the photothermal effect
Author(s): Karl-Heinz Walker; Heinz Sontag
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Paper Abstract

A fiber optic sensor system based on the photothermal effect has been developed and applied to very low concentration measurements in solutions. The sensor head comprises three closely spaced optical fibers for excitation, probe, and reflected probe light. A combination of reflective and refractive miniature optics is used to focus the respective beams into the probe volume. If an absorbing substance is present, the absorbed light power from the modulated excitation beam generates a refractive index gradient in the probe volume, which can be observed via deflection measurements of the non-absorbing cw probe beam. The reflective probe beam signal detected after phase synchronous demodulation is proportional to the substance concentration. Using a monochromatic lightsource with variable wavelength it is possible to discriminate different substances. With this system, we have analyzed Cu-II concentrations in galvanic solutions from 1000 ppm down to concentrations below 1 ppm, thus reaching the sensitivity for waste-water control. Applications for this chemical sensor system are in-line environmental and pollution control of water due to its very high sensitivity. The large dynamic range also makes it suitable for various in-line process control tasks.

Paper Details

Date Published: 1 September 1991
PDF: 6 pages
Proc. SPIE 1510, Chemical and Medical Sensors, (1 September 1991); doi: 10.1117/12.47140
Show Author Affiliations
Karl-Heinz Walker, Dornier GmbH (Germany)
Heinz Sontag, Dornier GmbH (Germany)

Published in SPIE Proceedings Vol. 1510:
Chemical and Medical Sensors
Otto S. Wolfbeis, Editor(s)

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