Real-time stand-off spatial detection and identification of gases and vapor using external-cavity quantum cascade laser open-path spectrometer

An open-path spectrometer for fast spatial detection and identification of gaseous plumes in a realistic environmental conditions is presented. Gases are released in a 500 m3 hall; detection and identification is performed by spectroscopic means—measuring the light spectral absorption (at 8 to 10 μm) by shining an external-cavity quantum cascade laser beam through the inspected volume. Real-time identification is demonstrated for gas plumes of CH2FCF3 (R134a) and CHF3 at a distance of 30 m round trip with a minimum identification level of 0.2 ppm (response times of 2 to 10 s). The relatively wide spectral coverage allows a high probability of detection (PD) and low probability for a false alarm to be obtained in these realistic conditions. It is also demonstrated that the use of several lines-of-sight improves PD as gas spreading in the hall in these conditions is slow and unpredictable.