Abstract
Using infrared hyperspectral imaging, microscopy of small particles of the explosives compounds RDX, tetryl, and PETN with near diffraction-limited performance is demonstrated. The custom microscope apparatus includes an external cavity quantum cascade laser illuminator scanned over its tuning range of 9.13 to 10.53 μm in 4 s, coupled with a microbolometer focal plane array to record infrared transmission images. The hyperspectral microscopy technique is used to study the infrared absorption spectra of individual explosives particles, and demonstrate subnanogram detection limits.
Highlights
Hyperspectral imaging using broadly tunable external cavity quantum cascade lasers (ECQCLs) offers the potential for high-speed chemical imaging of gas, liquid, and solid compounds over a wide range of magnifications
We have previously demonstrated hyperspectral imaging using ECQCL illumination in both transmission and reflection geometries; the spatial resolution of these systems was limited as they were designed for imaging large fields-of-view.[1,2]
It is worth noting that the high spectral brightness of the ECQCL source allows transmission through thick particles with high absorption
Summary
Hyperspectral imaging using broadly tunable external cavity quantum cascade lasers (ECQCLs) offers the potential for high-speed chemical imaging of gas, liquid, and solid compounds over a wide range of magnifications. Operating in the mid-infrared (MIR) “fingerprint” spectral region of 3 to 25 μm, ECQCLs provide a high-brightness tunable laser source for infrared spectroscopy and imaging. Microscopic chemical imaging in the MIR spectral region is often performed using Fourier-transform infrared (FTIR) spectroscopy techniques.[4,5,6] the low spectral radiance of the broadband thermal illumination source places limitations on this technique. Many of the limitations can be overcome using synchrotron radiation sources to provide a higher spectral radiance,[7,8,9] but these systems can have a high cost and low availability
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