MIR sensors and measuring technology are particularly suited to detect chemical substances. Dr. Ostendorf, what are the main strengths when compared to other sensor technologies?

The medium infrared range of 4 – 12 μm is of particular interest to spectroscopy, as this is where the basic modes of the combined vibrational modes of many chemical substances are found. The resulting absorption bands are characteristic, just like a fingerprint, and thus allow for unequivocal identification of chemical compounds. Light with the right wavelength is particularly well absorbed in this range. Other optical measuring methods, such as those in the near-infrared wavelength around 1 μm, only measure the higher orders – echoes of a sort – of these basic oscillations, and these exhibit much less extensive absorption. For this reason, much higher sensitivity and selectivity can be achieved in the mid-infrared range.

You specialize in the development of semiconductor lasers for the infrared wavelength. What advantages do these lasers offer?

One main application of our MIR lasers is sensors and spectroscopy. In general, lasers offer a very high light density, which can also be easily focused or collimated onto a point or towards a certain area. The high spectral brightness, for example, allows uncooled detectors to be used in sensor systems with MIR lasers. A complex cooling system using liquid nitrogen, as usually found within this wavelength range, is not necessary. This means that systems of this kind can be made smaller and more compact. Furthermore, MIR lasers offer the option of investigating very absorbent substances within this spectral range, such as water, as a laser is capable of penetrating much thicker films of water than e.g. a conventional light source for infrared, or an LED. The property of bundling the laser light across a long distance opens up the option of measurements with stand-off capability. We were thus able to demonstrate the presence of the tiniest traces of explosives from a distance of more than 20 m.

Fraunhofer IAF already produces specifically adapted sensors and measurement setups. Which applications do you find particularly exciting and what do you expect the future to bring?

Together with Fraunhofer IPMS, we continued to shrink the laser source and considerably increased the speed at which the wavelength is tuned. We are now able to detect chemical substances with our MIR semiconductor lasers within a few milliseconds. This advance into real-time spectroscopy offers great potential. It allows analysis of large samples within a very short time, as required, for example, for 100 % inspection during pill manufacture in the pharmaceuticals industry. The miniaturization of the laser source offers great opportunities for realizing handheld and compact sensor devices.

Within the EU’s “MIRPHAB” pilot line, you are working with many institutes and companies from the MIR sector. What do you hope this collaboration will bring?

Nowadays, new technologies need to be developed along the complete value chain, up to and including demonstrators and prototypes. No single institute or company can master this challenge alone. MIRPHAB offers us a way of bundling our skills from all areas of MIR sensor systems and from all across Europe. That is the only way we can remain competitive in the long term.

Dr. Ostendorf, thank you very much for talking to us.

The Interview was conducted by Maximilian Kunze.

About Ralf Ostendorf:

After obtaining his doctorate in physics at the University of Münster in 2005, Ralf Ostendorf joined Fraunhofer IAF in Freiburg as a research associate and project manager. There, he first worked on the development of GaAs-based highbrightness diode lasers. In 2009, he moved to the area of quantum cascade lasers (QCLs) in the infrared wavelength range, concentrating on the development of wavelength-adjustable QCLs for infrared spectroscopy. He has managed several national and international projects covering this topic. Since the beginning of 2016, Dr. Ralf Ostendorf is responsible for the Semiconductor Lasers business unit at Fraunhofer IAF.