Abstract
A trace chemical detector is described that combines external-cavity quantum cascade lasers and a mercury cadmium telluride camera to capture hyperspectral images of the diffuse reflectance from a target surface in the long-wave infrared. The system is able to generate individual hypercubes in <0.1 s. When raster scanning the laser beam over the target surface, areal coverage rates of >60 cm2 / s have been achieved. Results are presented for standoff distances ranging from 0.1 to 25 m. Hyperspectral images generated by the system are analyzed for spectral features that indicate the presence of trace surface contaminants. This approach has been found to be highly capable of detecting trace chemical residues on a wide variety of surfaces, and we present a collection of detection results to demonstrate the capabilities of this technology. Examples include the detection of 10 μg of saccharin powder on a wide range of substrates, 0.2 μg of an explosive residue on a computer keyboard, residual pharmaceuticals within a plastic baggie, and a contaminated fingerprint on cell phone case.
Highlights
Hyperspectral images generated by the system are analyzed for spectral features that indicate the presence of trace surface contaminants. This approach has been found to be highly capable of detecting trace chemical residues on a wide variety of surfaces, and we present a collection of detection results to demonstrate the capabilities of this technology
Laser-based long-wave infrared (LWIR) hyperspectral imaging is shown to be a powerful method for the standoff detection, identification, and mapping of trace chemicals on surfaces
It is our opinion that LWIR reflectance spectroscopy is uniquely suited to combining high-sensitivity chemical detection with the ability to rapidly scan surfaces with high areal coverage rate (ACR) while remaining eye safe
Summary
Standoff detection of trace chemicals on surfaces is of great importance for a variety of commercial, law enforcement, intelligence, and military applications, such as explosives detection, drug detection, forensic analysis, contamination avoidance, border protection, cleaning validation, and process monitoring.[1,2] Sensitive techniques, such as mass spectrometry and ion-mobility spectrometry, exist for trace chemical sensing, but these require a physical transfer of the chemicals into the instrument.[3,4] there are many situations in which physical sampling is not feasible and it is highly desirable to perform noncontact and nondestructive testing at appreciable standoff distances (>1 m).[5]. This means that relatively low power LWIR lasers can be used to achieve high-sensitivity detection. It is our opinion that LWIR reflectance spectroscopy is uniquely suited to combining high sensitivity chemical detection with the ability to rapidly scan surfaces with a high areal coverage rate (ACR) while remaining eye safe. The LWIR is the probably the most important band for standoff detection because of (i) the high degree of atmospheric transparency, and (ii) the existence of rich spectra for the largest fraction of chemicals of interest
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