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Fast laser keeps an eye on complex chemical reactions

12 June 2015

Fraunhofer scientists have developed a novel infrared laser device that can monitor chemical reactions in real time, offering an alternative to offline sample analysis.

Fraunhofer's quantum cascade laser records 1,000 spectra/second (photo: Fraunhofer IAF)

To verify that a chemical reaction has proceeded as desired, samples are usually taken from the reaction vessel and examined in a laboratory, where chromatographic or spectroscopic analyses are applied. These are costly and tedious processes that only allow investigation based on random samples.

This might soon be simplified with the help of a novel infrared laser developed by researchers at the Fraunhofer Institutes for Applied Solid State Physics IAF in Freiburg and for Photonic Microsystems IPMS in Dresden.

"Our quantum cascade lasers facilitate a new kind of spectroscopy,"says Dr Ralf Ostendorf, project manager at Fraunhofer IAF. "The process of chemical reactions - for example, in the development of new pharmaceuticals - could soon be continuously monitored in real time, rather than analysing random samples, as done in current monitoring processes."

The laser directs infrared light into the reaction vessel where the substances it contains absorb a portion of the light; the rest is scattered back and analysed by a detector. Each substance absorbs the light at different specific wavelengths. The result is an absorption spectrum which allows to precisely identify each substance.

With this kind of spectrometer, it might soon be possible to determine with precision the concentration of the reactant materials in the reaction vessel as well as the quantities already transformed into the end product - and at any point of time during the reaction process.

however, in order to achieve this, the laser needs to meet several requirements: the emitted laser light should consist of one specific wavelength only and, moreover, has to be constantly adjustable over a vast spectral range. Thus, the laser light initially has a short wavelength which is gradually increased up to a designated value, before the procedure restarts from the beginning.

The detector then determines for each wavelength, how much light is scattered back by the respective sample. A further challenge concerns the process of switching the laser's emission wavelength, which has to be as fast as possible.

Hitherto, a laser would need a few seconds to tune through every wavelength and to determine the actual state of the chemical reaction being analysed. Researchers from Fraunhofer IPMS have been able to increase this speed by a factor of 1,000 by applying a micro-mechanical scanning mirror. Instead of one spectrum per second, they now succeed in recording 1,000 spectra per second.

The laser is just barely larger than a matchbox. It is not only suitable for the reaction vessels used in the pharmaceutical and chemical industry, but also small enough to be used in a hand-held device that would allow a police officer or customs officer to inspect suspicious substances both quickly and easily.

The researchers aim to produce a prototype of the laser by the end of 2015. However, you can see the concept at the 'Laser - World of Photonics' event, which takes place from June 22 to 25 in Munich.

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