A standoff chemical detection system was developed to rapidly detect trace chemicals on surfaces. In only 0.1 s, the system can measure the long-wave infrared (LWIR) spectral reflectance from a surface over the wavelength range of 7.5 – 10.5 μm with a spectral resolution of 2 cm-1. Under these conditions, a signal-to-noise ratio (SNR) > 100 was demonstrated at standoff distances of 0.5 – 1.5 m. As a detection example, saccharin was detected on high-density polyethylene (HDPE) at a surface concentration of 30 μg/cm2. The high-speed acquisition capability was made possible by combining a thermoelectrically cooled single-pixel HgCdTe (MCT) detector, advanced acquisition electronics, and fast-tuning external-cavity quantum cascade lasers (EC-QCLs).
KEYWORDS: Contamination, Sensors, Long wavelength infrared, Quantum cascade lasers, Signal to noise ratio, Reflectivity, Image segmentation, Speckle, Chemical detection, Cameras
A hand-portable standoff trace chemical detection system was developed using a long-wave infrared (LWIR) microbolometer (MB) camera in combination with widely tunable external-cavity quantum cascade lasers. The system acquires hyperspectral images of the target surface’s reflectance in the LWIR portion of the “chemical fingerprint” band to allow for high-sensitivity detection and high-specificity identification of a wide range of surface chemicals. With a LiDAR-based autofocus, the system can measure targets at standoff distances as long as 15 m with clear chemical signatures in the resulting spectrum. Array scan measurements of powder and liquid chemicals at various standoff distances are presented and shown to enable the user to spatially locate trace contaminants on a variety of surfaces. Finally, the stability of the SNR is analyzed and shown to enable reference-free measurements, a significant step towards a versatile “point-and-click” LWIR-based standoff trace chemical detector.
A standoff trace chemical detection system to detect vehicle-borne threats was developed using a long-wave infrared (LWIR) microbolometer (MB) camera in combination with widely tunable external-cavity quantum cascade lasers. The system acquires hyperspectral images of the target surface’s reflectance in the LWIR portion of the “chemical fingerprint” band to allow for high-sensitivity detection and high-specificity identification of a wide range of surface chemicals. By using a MB camera, as opposed to more expensive alternatives, the system is targeted for applications that require small size and low cost. This talk describes the design and performance of the prototype.
Microcavity exciton-polaritons based on transition metal dichalcogenide monolayers (TMDs) are a promising platform for coherent valleytronics, exhibiting valley-dependent phenomena at room-temperature. Using polarization-dependent transient reflectance, we demonstrate the valley-exclusive nature of the optical Stark effect in WS2 exciton-polaritons. We observe a simultaneous shift of both polariton branches when pump and probe are co-polarized and no appreciable shift when they are cross-polarized, demonstrating a polarization-selective stark shift in exciton-polaritons. This work highlights how the unique features of TMD exciton-polaritons can give rise to new polaritonic phenomena.
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