Differential spectroscopic imaging of particulate explosives residue

Abstract

ABSTRACT We present experimental results showing transmission and reflection imaging of approximately 100 µg quantities of particulate explosives residue using a commercial uncooled microbolometer infrared camera and CO 2 laser differential wavelength illumination. Fine particulates may be generated during bomb-making activities and these particulates can tenaciously adhere to packing material, as well as to the clothing or skin of the bomb maker and could be detectable during transportation. A rapid screening method that detects this residue can serve as a first-line screening method in conjunction with more sensitive, but invasive, approaches. Explosives exhibit absorption features in the mid-infrared molecular fingerprint region that spans 3 to 15 µm, which can be probed with many high-brightness sources such as fixed wavelength and tunable quantum cascade lasers, CO 2 , CO, and OPO lasers. Commercial uncooled microbolometer cameras typically have detection sensitivity from 7.5 to 13 µm, spanning an absorption region for explosives detection with adequate signal-to-noise ratio. By illuminating a target on and off its absorption wavelengths, ratio images of suspected residue can be obtained without any sample preparation or cooperation and contact with the target. Our proof-of-principle experiment employed tunable CO