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Standoff detection from diffusely scattering surfaces using dual quantum cascade laser comb spectroscopy
Author(s): Joel M. Hensley; Justin M. Brown; Mark G. Allen; Markus Geiser; Pitt Allmendinger; Markus Mangold; Andreas Hugi; Pierre Juoy; Jérôme Faist
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Paper Abstract

Using dual optical frequency comb (OFC) spectroscopy in the longwave infrared (LWIR), we demonstrate standoff detection of trace amounts of target compounds on diffusely scattering surfaces. The OFC is based on quantum cascade lasers (QCL) that emit ~1 Watt of optical power under cw operation at room temperature over coherent comb bandwidths approaching 100 cm-1. We overlap two nearly identical 1250 cm-1 QCL OFC sources so that the two interfering optical combs create via heterodyne a single comb in the radio frequency (rf) that represents the entire optical spectrum in a single acquisition. In a laboratory scale demonstration we show detection of two spectrally distinct fluorinated silicone oils, poly(methyl-3,3,3-trifluoropropylsiloxane) and Krytox™, that act as LWIR simulants for security relevant compounds whose room temperature vapor pressure is too low to be detected in the gas phase. These target compounds are applied at mass loadings of 0.3 to 90 μg/cm2 to sanded aluminum surfaces. Only the diffusely scattered light is collected by a primary collection optic and focused onto a high speed (0.5 GHz bandwidth) thermoelectrically cooled mercury cadmium telluride (MCT) detector. At standoff distances of both 0.3 and 1 meter, we demonstrate 3 μg/cm2 and 1 μg/cm2 detection limits against poly(methyl-3,3,3-trifluoropropylsiloxane) and Krytox™, respectively.

Paper Details

Date Published: 8 May 2018
PDF: 8 pages
Proc. SPIE 10638, Ultrafast Bandgap Photonics III, 1063820 (8 May 2018); doi: 10.1117/12.2305190
Show Author Affiliations
Joel M. Hensley, Physical Sciences Inc. (United States)
Justin M. Brown, Physical Sciences Inc. (United States)
Mark G. Allen, Physical Sciences Inc. (United States)
Markus Geiser, IRsweep AG (Switzerland)
Pitt Allmendinger, IRsweep AG (Switzerland)
Markus Mangold, IRsweep AG (Switzerland)
Andreas Hugi, IRsweep AG (Switzerland)
Pierre Juoy, ETH Zurich (Switzerland)
Jérôme Faist, ETH Zurich (Switzerland)


Published in SPIE Proceedings Vol. 10638:
Ultrafast Bandgap Photonics III
Michael K. Rafailov, Editor(s)

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