Measuring accurate optical constants of uranium minerals for use in optical modeling of infrared spectra

Myers, Tanya L.; DeVetter, Brent M.; Saunders, Danielle L.; Lonergan, Charmayne; Yokosuk, Michael O.; Bernacki, Bruce E.; Bautista, Anjelica; Johnson, Timothy J.

doi:10.1117/12.2588321

Cited by 1 publication

(1 citation statement)

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“…Populating such databases is time-and labor-intensive, particularly if one takes into account the fact that different forms of the same material can result in significantly different signatures. 8,9 In its many forms (grazing, hemispherical, attenuated total reflectance [ATR]), infrared (IR) reflectance spectroscopy has become a truly powerful method to identify chemicals. However, these significant effects of the physical form of the sample and its environment on the resulting spectra can confound identification algorithms, and require more reference spectra; this is especially true for condensed-phase deposits and stains.…”

Section: Introductionmentioning

confidence: 99%

Using synthetic infrared spectra derived from n/k optical constants for standoff detection of chemical deposits

Lonergan

Erickson

Kelly-Gorham

et al. 2023

Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XXIV

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We report results from a recent field experiment to test the validity of using physics-based synthetic infrared spectra to serve as endmembers in a spectral database targeted at chemical deposits. Specifically, the optical constants n and k, (the real and imaginary part of the refractive index) were used to first model infrared reflectance spectra for different thicknesses of chemical layers (e.g. acetaminophen, methylphosphonic acid -MPA, etc.) on various conducting and insulating substrates such as aluminum, wood, and glass. In the experimental portion of the research, thin films of the solid and liquid analytes were deposited onto such substrates to form micron-thick layers of the analytes at different thicknesses: Standoff data from an imaging instrument were then recorded and analyzed to not only identify the different analytes, but also quantify the layer/deposit thickness. To gauge success, the detection results using the synthetic data were compared to the results from laboratory hemispherical reflectance (HRF) spectra that were collected for the same sample planchets measured in the field via standoff methods. Preliminary results indicate good agreement between the synthetic reference data as compared to the lab-measured HRF data in terms of their ability to quantitatively reduce longwave infrared data. Specifically, modeled IR spectra for acetaminophen on an aluminum planchet at various thicknesses (1, 2, 5, 10, 15, and 20 μm) were synthesized and compared with standoff field reflectance data as well as HRF laboratory reflectance spectra for two samples: a 5.2 μm-and 12.8 μm-thick layer of acetaminophen on aluminum. Using a first-order approximation, analysis of the field data estimates the thicknesses of the samples to be 2 and 10 μm for the two samples, respectively, while the HRF laboratory data yields thickness estimates of between 5-10 μm and 10 μm, respectively. Both yield reasonable estimates, with the uncertainty most likely due to factors yet to be accounted for in the synthetic spectra such as light scattering.

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Section: Introductionmentioning

confidence: 99%