Fraunhofer scientists develop MEMS spectrometer to detect hazardous chemicals

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At this years Photonics West, the Fraunhofer Institute for Photonic Microsystems (IPMS) will unveil a device the size of a sugar cube that can detect hazardous gasses, liquids and solids. The mobile MEMS scanning grating spectrometer works in the infrared spectral region to identify different materials, which, in the near future, could prove beneficial for use in airports, industrial plants and other locations where leakages could impact the environment and the general public.

Industrial accidents and oils spills are just a couple of examples of how humans and the environment are at risk from leaks of hazardous substances. The assessment of and timely response to possible risks requires that the type and concentration of substances can be qualitatively and quantitatively determined as quickly as possible.

As part of the European joint venture research project, MIRIFISENS – Mid Infrared Innovative Lasers for Improved Sensor of Hazardous Substances − the Fraunhofer IPMS and 17 other project partners from nine countries have been developing a portable variable-frequency monochromatic light source for the medium infrared range. It forms the basis for the development of handy spectrometers that can detect the concentration of different hazardous materials quickly on location.

The system consists of a miniaturised quantum cascade laser (QCL), which covers a large range of wavelengths in the medium infrared range.

To tune the light of the QCL to the defined wavelengths, Fraunhofer scientists developed a highly reflective diffraction grating with a diameter of just five millimetres, which acts as the laser's variable frequency external resonator. It allows for the tuning of laser wavelengths with a frequency of 1,000Hz, with a variable frequency range of up to 20 per cent of the central wavelength.

In this way, the sample can be irradiated with different wavelengths in the time multiplex, and conclusions can be drawn with regard to the type and concentration of the hazardous materials using the spectral fingerprint.

‘Electrostatically-driven MEMS grating mirrors are much more compact than galvanometer scanners, make almost no sound and allow for very high scanning frequencies due to their low weight,’ explained Fraunhofer IPMS' project manager Dr Jan Grahmann. ‘In combination with miniaturised laser sources, they are ideal for integration into mobile handy sensor systems, simple measurements on location and for integration into industrial measurement technology at production and processing facilities.’

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Further information

Fraunhofer IPMS' MEMS Scanners