Mid-Infrared Standoff Detection of Explosives Using a Tunable EC-QCL

Abstract

There has been a fundamental change in security risk for society within the last years. Especially terror attacks like in Cucuta (2021), Kabul (2021) or Brüssel (2016) have shown how important it is to protect critical infrastructures such as airports. Fast and reliable detection of hazardous trace materials is one key for achieving improved safety standards in the future. In that context, remote detection of explosive materials is of great interest, as it allows for threat detection without putting people in harms way. Therefore, it is imperative to develop chemically selective and sensitive methods to detect such materials from a safe distance. For this reason, we are developing a new standoff mid infrared spectroscopy system at the DLR Institute of Technical Physics. The system based on a widely tunable (from 6.1 to 11 µm) quantum cascade laser is able to capture multiple vibrational spectroscopic signatures of the explosives and thus highly selective. The high repetition rate of the laser and a detection scheme with a large signal-to-noise ratio result in a system with a very high sensitivity which allows for the detection of traces of explosives on various background materials. A detection system for field employment does not only have to detect traces of explosives but also needs to automatically raise an alarm in the event of the detection of a hazardous material. Therefore, a model is developed to classify our data into several groups, i.e. explosives and non-explosives. Measurements of various explosive and non-explosive substances on different background materials have been performed at a distance of roughly one meter. To characterize the influence of the sample orientation on the signal strength and spectral shape, the samples have been detected at different angles as well. During the presentation, the developed system as well as performed measurements and first results of the model to classify the data will be presented.