Enabling standoff detection of hazardous materials using a fiber optic coupled quantum cascade infrared laser system

The global defense community requires new approaches for standoff detection of chemical, biological, radiological, nuclear and explosive (CBRNE) threats. Such standoff detection methods must be capable of discriminating the target hazardous materials from the environmental background. Therefore these sensors must exhibit high selectivity. High selectivity detection of CBRNE threats can be accomplished using infrared (IR) spectroscopy, which produces a unique spectral “fingerprint” of the target chemical, enabling discrimination of the target chemical from other chemicals in the background. Standoff detection using IR spectroscopy however requires that enough of the incident source light may be collected at the detector; therefore a high-power source is needed. Commercially available quantum cascade laser (QCL) sources are capable of projecting high power, coherent laser light at targets down range from the source. In order to collect complete IR spectra throughout the entire fingerprint region, the output of multiple QCL modules are combined into a single exit aperture. This is typically achieved using mirrors and other optics which are susceptible to vibrational and temperature misalignments in field systems. In order to provide a more ruggedized solution to combining the beam output of multiple QCL modules, we developed a unique chalcogenide optical fiber beam combiner which combines the output of four commercial QCL modules. This allows for scanning across a spectral range from 6.01 – 11.20 μm encompassing parts of both the IR functional groups and fingerprint regions. We demonstrate the ability of this QCL system to generate high quality IR spectra of hazardous materials.