What is your academic background?
Christoph: I obtained my PhD from the University of Konstanz. The main topic was sum-frequency microscopy based on ultrafast high-repetition-rate laser systems. Now, I am a group leader at the German Aerospace Center in the Institute of Technical Physics where we develop compact systems for the detection of chemical, biological and explosive substances (CBE).
Anja: I am a chemist and have a PhD in physical chemistry from Kiel University where I mainly worked on ultrafast laser spectroscopy with photo-switchable molecules. Now, I am also a group leader at the DLR and work on the development of detection systems for CBE substances.
What are the core competencies of the DLR institutes?
Christoph: The DLR has four pillars: aerospace, astronautics, traffic and energy. Additionally, there are the areas of security and digitalization which span across all four pillars. Our groups belong to the security section.
Please tell us about your project related to the detection of explosives.
Anja: PHYLAX is a project which came out of discussions with the police and other end users who are keen to have a contactless detection system for explosives. The goal is to speed up security processes; for example, at airports. We came up with the idea of a laser-based system to detect traces of explosives on surfaces. In our project, we focus on the surfaces of shoes, but in principle, it works with every surface, like luggage, hands, or cars. For the detection, we examine the surface using UV Raman spectroscopy and mid-infrared (MIR) absorption spectroscopy simultaneously. Both data sets are evaluated to decide whether there are traces of explosives or not. The combination of these two techniques ensures that we can detect explosives in a variety of situations – even if one technique does not detect the traces, they will be detected by the other technique. We have also implemented a tracking system to make sure the system scans the shoe and not the floor.
How is the detection system implemented?
Christoph: The MIR absorption spectroscopy is a stand-off system (L. B. Dreier et. al. Sensors 22, 7839 (2022)) using a pulsed quantum cascade laser with a repetition rate of 1 MHz. We tune over a broad spectral range from about 6.5 µm to about 11.5 µm and measure the scattered light. For signal detection, we use the UHF-BOX Boxcar Averager and subtract the background signal from the laser signal.
For tracking, we use a 3D camera system to create an estimation of the person and find the position of the shoe. We then direct our laser beams with a scan mirror to the middle of the shoe and scan over the shoe area. The alignment is completely automatic.
What is especially promising about this approach in your view?
Anja: Our laser-based detection system is fast and can detect traces of explosives while you are doing other things like putting your luggage on the belt: you don’t need to stand still and wait for the scan to finish.
What are the next steps?
Anja: Currently, we have a research model demonstrating that the principle is working. In the next steps, we want to demonstrate the technique in a real environment. We have been in contact with end users during the entire project to get input and feedback and now we are at a point where we will work closer together to reach the prototype level.
You work on a variety of projects – can you also tell us about the VinoLAS project?
Christoph: In the VinoLAS project, we use fluorescence spectroscopy to detect pathogenic fungi on wine leaves. Similar to the PHYLAX project, we started by setting up a research model in the lab where we used the UHF-BOX Boxcar Averager to measure the excited fluorescence from nanosecond or picosecond laser pulses. More recently, we developed a compact measurement system and can now perform measurements directly in the vineyards.
Did the project include a wine tasting?
Christoph: (Laughs.) We drank grape juice after our successful measurement in the vineyard.
What are your plans for the next projects?
We are working on a new DLR internal project for gas-phase detection. The goal is to set up a drone-based system for detecting the leakage of gases. The entire optics will be on the drone, which means we need to design a very compact system.
What do you like to do in your free time?
Anja: I like climbing, reading, and just relaxing.
Christoph: I am training for a triathlon - but only for fun, not for Iron Man.
