21 January 2012 Sub-ppb detection of nitrogen dioxide with an external cavity quantum cascade laser
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Proceedings Volume 8268, Quantum Sensing and Nanophotonic Devices IX; 82682H (2012); doi: 10.1117/12.908402
Event: SPIE OPTO, 2012, San Francisco, California, United States
Ultra-sensitive detection of nitrogen dioxide (NO2) in the ν3 fundamental band of NO2 using Faraday Rotation Spectroscopy (FRS) based optical sensor platform is reported. The FRS technique is well suited for selective trace gas measurements of paramagnetic species including the prominent air pollutants such as NO or NO2. In this paper a widely tunable external cavity quantum cascade laser (EC-QCL) is employed as an excitation source. The available EC-QCL mode-hop free tuning range between 1600 cm-1 and 1650 cm-1 allows to access the optimum for FRS technique 441<-440 Q-branch NO2 transition at 1613.2 cm-1 with an optical power of ~135 mW. In order to improve detection sensitivity and reduce size of the sensor platform, a custom made 22.47 cm long Herriott multipass gas cell (MPC) with a total effective optical path of 10.1 m was implemented. For a MPC configured NO2 FRS sensor operating in line-scanning mode a minimum detection limit of 1.6 ppbv (1σ) and 0.15 ppb (1σ) is achieved for a 1 sec and 100 sec averaging time, respectively. Preliminary results for long term measurements of atmospheric NO2 for the FRS sensor operating at an optimal pressure of 30 Torr and magnetic field of 200 Gaussrms were demonstrated.
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Rafal Lewicki, Kun Liu, Timothy Day, Frank K. Tittel, "Sub-ppb detection of nitrogen dioxide with an external cavity quantum cascade laser", Proc. SPIE 8268, Quantum Sensing and Nanophotonic Devices IX, 82682H (21 January 2012); doi: 10.1117/12.908402; https://doi.org/10.1117/12.908402




Signal detection


Quantum cascade lasers

Signal to noise ratio


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