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Emerald Group Publishing Limited
Copyright © 1998, MCB UP Limited
A minisensor that is over 50 times more sensitive than conventional absorption spectroscopy detectors has been developed by the Karlsruhe Research Centre (Karlsruhe, Germany). The device may be used for measuring the concentration of a specific product or contaminant in a fluid stream. Potential applications include high-performance liquid chromatography, or in-line monitoring of dyestuffs in textile and dye industry effluent streams.
Process liquid flows through a channel in the sensor, which is housed in a 2 x 2 x 2cm box. The liquid is irradiated by a pulsed neodymium-yttrium-aluminium-garnet or argon-ion laser and its light-absorbing molecules release heat, creating a refractive-index gradient in the solution that is known as a thermal lens(TL). A second, non-absorbable light beam (e.g. from a helium-neon laser) is directed through the TL. This changes the intensity of the beam, the change being proportional to the concentration of the component being measured.
So far, thermal lensing has not been suitable for routine analysis because of the need for critical laser alignment and the expertise required of the operator. However, the minisensor's compact size has virtually eliminated these problems. FZK is working with German companies and expects to have an industrial prototype in 1997.