[Zurück]

C. Reidl-Leuthner, B. Lendl:
"Determination of NO & NO2 Emissions Using an Open-Path / QCL Setup";
Poster: International Quantum Cascade Lasers School & Workshop 2012, Baden bei Wien; 02.09.2012 - 06.09.2012; in: "International Quantum Cascade Lasers School & Workshop 2012 - Workbook", (2012), ISBN: 978-3-901578-24-3; S. 171.

Open-path measurements using conventional mid-infrared (MIR) sources have been used for decades in environmental and process monitoring [1]. The advantage of these measurements is the quantification of contaminants in the line-of-sight of the instrument without the need of sample preparation or direct access to the surveyed area. The introduction of QCLs with their sharp emission bands and high spectral power density has the potential to improve selectivity and sensitivity with which analytes are detected. In addition, these short pulsed QCLs can facilitate a reduction in the measuring time and can be used in open-path measurements up to a few kilometers [2].

Initially the QCLs were characterized via step scan measurements using a Bruker 80V FTIR spectrometer. During a single pulse the complete spectral information of the pulse was obtained. These QCLs were then introduced into the open-path system in Figure 1. Two QCLs operating at approx. 1901cm-1 and 1632cm-1 were used for the determination of NO and NO2 respectively. The absorption of light by these analytes along the open-path measurement is determined as the laser beams are reflected by a retro-reflector and focused on a thermoelectrically cooled MCT detector. For calibration purposes it is possible to place a reference cell containing NO and NO2 in the path using standard addition.



Using the spectral information, changing the temperature of the QCL during the 300ns pulse it is possible to scan the over one or two rotational bands of the analyte (Figure 2). This allows the determination of the concentration during one pulse, as the blank can be measured with the intensity of the peak before and after the absorption band. Alternatively it is also possible to determine the concentration using the known ratio of two ro-vibrational states.

[1] G. Russwurm and J. Childers, "Handbook of vibrational spectroscopy", edited by J. Chalmers and P. Griffiths. John Wiley & Sons, Chichester, 1779-1802 (2002)

[2] M. Taslakov, V. Simeonov, M. Froidevaux and H. Van Den Bergh, "Open-path ozone detection by quantum cascade laser", App. Phys. B82, 501-506 (2006)

QCL, Open-Path, Emisssion Monitoring, NO, NO2