Compact IR spectrometer with outstanding capabilities

Small IR spectrometer

ETH researchers have developed a compact infrared spectrometer. It’s small enough to fit on a computer chip but can still open up interesting possibilities – in space and in everyday life.

Nowadays, a mobile phone can do almost anything: take photos or video, send messages, determine its present location, and of course transmit telephone conversations. With these versatile devices, it might even be possible to ascertain a beer’s alcohol content or how ripe a piece of fruit is.

At first glance, the idea of using mobile phones for chemical analyses seems a daring one. After all, the infrared spectrometers used for such analyses today generally weigh several kilograms and are difficult to integrate into a handheld device. Now researchers at ETH Zurich have taken an important step towards turning this vision into reality. David Pohl and Marc Reig Escalé, in the group headed by Rachel Grange, Professor of Optical Nanomaterials in the Department of Physics, collaborated with other colleagues to develop a chip about 2 square centimeters in size. With it, they can analyse infrared light in the same way as they would with a conventional spectrometer.

Waveguides instead of mirrors

A conventional spectrometer splits the incident light into two paths before reflecting it off two mirrors. The reflected light beams are recombined and measured with a photodetector. Moving one of the mirrors creates an interference pattern, which can be used to determine the proportion of different wavelengths in the incoming signal. Because chemical substances create characteristic gaps in the infrared spectrum, scientists can use the resulting patterns to identify what substances occur in the test sample and in what concentration.

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Credit: “Smaller than a coin”, Felix Wursten, ETH Zurich