Fiber optic based chemical sensor system for in-situ process           measurements using the photothermal effect

Karl-Heinz Walker; Heinz Sontag

doi:10.1117/12.47140

1 September 1991 Fiber optic based chemical sensor system for in-situ process measurements using the photothermal effect

Karl-Heinz Walker, Heinz Sontag

Author Affiliations +

Proceedings Volume 1510, Chemical and Medical Sensors; (1991) https://doi.org/10.1117/12.47140
Event: ECO4 (The Hague '91), 1991, The Hague, Netherlands

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.

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Karl-Heinz Walker and Heinz Sontag "Fiber optic based chemical sensor system for in-situ process measurements using the photothermal effect", Proc. SPIE 1510, Chemical and Medical Sensors, (1 September 1991); https://doi.org/10.1117/12.47140

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KEYWORDS

Sensors

Fiber optics sensors

Laser beam diagnostics

Signal detection

Fiber optics

Modulation

Photothermal effect

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