Quantum cascade laser tests water for impurities on-site

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Researchers at the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg have developed a spectrometer for testing drinking water for impurities based on a quantum cascade laser. The device allows water companies to identify impurities in the water on-site, at the waterworks, previously not possible with standard spectrometers.

A demonstrator has already successfully undergone initial practical testing at the Kleine Kinzig waterworks in the Black Forest. Tests were conducted on various concentrations of sweetener as a stimulant substance. Measurements were taken every three minutes over a period of six weeks, with the fully automated system collecting a total of 21,000 samples.

‘The equipment samples the water for dangerous substances at the waterworks itself in the course of routine operations, and allows for a rapid response,’ said Dr Frank Fuchs, coordinator for the IRLSENS project at Fraunhofer IAF. IRLSENS is funded by Germany’s Federal Ministry of Education and Research (BMBF).

The chemical constituents of the water sample are examined use molecular spectroscopy under infrared light. Each chemical compound has a unique spectrum, since individual molecules vibrate and absorb light at characteristic frequencies. Water itself is a very strong absorber of infrared light; since the light sources employed to date have delivered little power, until now examinations of this sort have only been possible in a laboratory setting.

‘The main sticking point is the intensity of the light. In order to be in a position to employ molecular spectroscopy at the waterworks itself, we needed to find a more powerful light source,’ explained Fuchs.

Fraunhofer IAF’s quantum cascade laser produces light that is up to 1,000 times more concentrated than the silicon carbide thermal emitters used in standard laboratory equipment. For molecular spectroscopy, analysts are interested in wavelengths between 7.3µm and 11µm.

The measurement system is only a little larger than a shoebox, works automatically, and requires hardly any maintenance.

Providing there is sufficient demand, project partner Bruker Optik, the company that built the demonstrator for the Kleine Kinzig waterworks, plans to develop the measurement system into a finished product.