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The Nerve gases are persistent gases that appear as very challenging menace in homeland security scenarios, due to the
low pressure vapor at ambient temperature, and the very low lethal concentrations. A novel approach to the detection and
identification of these very hazardous volatile compounds in large areas such as airports, underground stations, big
events arenas, aimed to a high selectivity (Low false alarm probability), has been explored under the SENSEFIB
Corporate Project of Finmeccanica S.p.A. The technical demonstrator under development within the Project is presented.
It is based on distributed line sensors performing infrared absorption measurements to reveal even trace amounts of
target compounds from the retrieval of their spectral fingerprint. The line sensor is essentially constituted by a widely
tunable external cavity quantum cascade laser (EC-QCL), coupled to IR thermoelectrically cooled MCT fast detectors by
means of a infrared hollow core fibers (HCF). The air is sampled through several micro-holes along the HCF, by means
of a micropump, while the infrared radiation travels inside the fiber from the source to the detector, that are optically
coupled with the opposite apertures of the HCF. The architecture of the sensor and its principle of operation, in order to
cover large areas with a few line sensors instead of with a grid of many point sensors, are illustrated. The sensor is
designed to use the HCF as an absorption cell, exploiting long path length and very small volume, (e.g fast response), at
the same time. Furthermore the distributed sensor allows to cover large areas and/or not easily accessible locations, like
air ducts, with a single line sensor by extending the HCF for several tens of meters. The main components implemented
in the sensor are described, in particular: the EC-QCL source to span the spectral range of wavelength between 9.15um
and 9.85um; and the hollow core fiber, exhibiting a suitably low optical loss in this spectral range (<1dB/m). Also, the
characteristics of detectors and associated electronics for signal processing and data acquisition are discussed. Main
results from preliminary measurements carried out are also presented.
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