Multiplexed dual-core QCL-based sensor for real-time standoff-spectroscopy in crime scene investigations

Conventional crime scene investigation is slow as traces are collected at the scene and are only subsequently analyzed in the lab. Rapid and contactless detection and examination of various trace materials at the scene without alteration is highly desirable as it avoids degradation of traces, significantly speeds up the investigations, and reduces the time to capture the perpetrator. Furthermore, contactless identification is crucial in guaranteeing the health and safety of crime scene investigators for chemical or explosive threats. Here we present a quantum-cascade laser-based backscattering infrared sensor that allows instantaneous detection and identification of a wide range of forensic relevant samples, from explosives to drugs, and precursors to bodily fluids. The system is based on external-cavity tunable quantum cascade lasers (EC-QCL) using resonant MOEMS (micro-opto-electromechanical system scanners) diffraction gratings, offering kilohertz spectral scan speeds. Two such MOEMS EC-QCL modules are multiplexed in the system and spectrally combined into a single laser beam. The (scalable) approach almost doubles the spectral coverage and increases the selectivity without sacrificing spectral scan speed. We report here on the system design and show first results.