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12 February 2008 A quantum cascade laser based room temperature spectrometer for sensitive detection of ammonia and ethylene
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Abstract
We investigated the use of a pulsed, distributed feedback (DFB) quantum cascade (QC) laser centered at 970 cm-1 in combination with an astigmatic Herriot cell with 150 m path length for the detection of ammonia and ethylene. This spectrometer utilizes the intra-pulse method, where a linear frequency down-chirp, that is induced when a top-hat current pulse is applied to the laser, is used for sweeping across the absorption line. This provides a real time display of the spectral fingerprint of molecular gases, which can be a few wave numbers wide. A 200 ns long pulse was used for these measurements which resulted in a spectral window of ~1.74 cm-1. A room temperature mercury-cadmium-telluride detector was used, resulting in a completely cryogen free spectrometer. We demonstrated detection limits of ~3 ppb for ammonia and ~5 ppb for ethylene with less than 10 s averaging time.
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J. Manne, W. Jäger, and J. Tulip "A quantum cascade laser based room temperature spectrometer for sensitive detection of ammonia and ethylene", Proc. SPIE 6900, Quantum Sensing and Nanophotonic Devices V, 690014 (12 February 2008); https://doi.org/10.1117/12.785478
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