Standoff detection from diffusely scattering surfaces using dual quantum cascade laser comb spectroscopy

Joel M. Hensley; Justin M. Brown; Mark G. Allen; Markus Geiser; Pitt Allmendinger; Markus Mangold; Andreas Hugi; Pierre Juoy; Jérôme Faist

doi:10.1117/12.2305190

8 May 2018 Standoff detection from diffusely scattering surfaces using dual quantum cascade laser comb spectroscopy

Joel M. Hensley, Justin M. Brown, Mark G. Allen, Markus Geiser, Pitt Allmendinger, Markus Mangold, Andreas Hugi, Pierre Juoy, Jérôme Faist

Author Affiliations +

Proceedings Volume 10638, Ultrafast Bandgap Photonics III; 1063820 (2018) https://doi.org/10.1117/12.2305190
Event: SPIE Defense + Security, 2018, Orlando, FL, United States

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/cm²to 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.

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Joel M. Hensley, Justin M. Brown, Mark G. Allen, Markus Geiser, Pitt Allmendinger, Markus Mangold, Andreas Hugi, Pierre Juoy, and Jérôme Faist "Standoff detection from diffusely scattering surfaces using dual quantum cascade laser comb spectroscopy", Proc. SPIE 10638, Ultrafast Bandgap Photonics III, 1063820 (8 May 2018); https://doi.org/10.1117/12.2305190

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