Rapid and sensitive standoff measurement techniques are needed for detection of trace chemicals in outdoor plume releases. Here, we present results from 235 m standoff detection of transient plumes for 5 gas-phase chemicals: Freon 152a (1,1-difluoroethane), Freon 134a (1,1,1,2-tetrafluoroethane), methanol (CH3OH), nitrous oxide (N2O), and ammonia (NH3). A swept-ECQCL measures infrared absorption spectra over the range 8.37- 10.47 µm, from which chemical concentrations are determined via spectral fits. The fast 400 Hz scan rate of the swept-ECQCL enables measurement above the turbulence time-scales, reducing noise and allowing plume fluctuations to be measured. For high-speed plume detection, measurement precisions of 1-2 ppm*m are demonstrated with 2.5 ms time resolution, improving to 100-400 ppb*m with 100 ms averaging.
Revised: March 18, 2020 |
Published: March 2, 2020
Citation
Phillips M.C., B.E. Bernacki, S.S. Harilal, J. Yeak, and R. Jones. 2020.Standoff chemical plume detection in turbulent atmospheric conditions with swept-wavelength external cavity quantum cascade lasers.Optics Express 28, no. 5:7408-7424.PNNL-SA-149581.doi:10.1364/OE.385850