P9 - Applying CEAS Method to Investigation of NO and N2O Absorption Lines in Infrared Spectra
- Event
- SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Nürnberg - Band
- Proceedings IRS² 2011
- Chapter
- IP - Poster Session
- Author(s)
- R. Mędrzycki, J. Mikołajczyk, J. Wojtas, Z. Bielecki, D. Szabra - Military University of Warsaw (Poland)
- Pages
- 134 - 138
- DOI
- 10.5162/irs11/ip9
- ISBN
- 978-3-9810993-9-3
- Price
- free
Abstract
The paper presents a project of the system designed to NO and N2O absorption coefficients measurements. In the system was applied one of the most sensitive optoelectronic gas detection technique - Cavity Enhanced Absorption Spectroscopy (CEAS). The absorption coefficient is determined by measurements of decay time of a laser pulse reflected inside an optical cavity. The measurement procedure consists of two steps. First, in case of lack of tested gas, decay time is determined. It gives value of measurement baseline. Next, decay time measurement is made again when the cavity is filled with tested gas.
The setup includes an optical cavity built with spherical mirrors of high reflectance. The optical signal is registered with a specially developed low noise photoreceiver. Optical radiation from the laser should be appropriate matched to the absorption spectrum of measured gas. Properly selected wavelength of laser radiation significantly determines sensitivity of the sensor. To analyze NO
and N2O absorption lines HITRAN database was used. It is noticed, that sensor optimal parameters (sensitivity and selectivity) can be achieved in spectral regions: 5.23 mm – 5.29 mm for NO and 4.46 mm – 4.54 mm for N2O. There will be applied two singlemode quantum cascade lasers (QCL), the spectra of which can be precisely tuned with temperature or current modulation. QCL emission lines are very narrow and also are characterized by both high power and good spectral stability. The radiation leaving the cavity will be registered with detection module consists of HgCdTe (MCT) detector and low noise transimpedance amplifier. Such system provide possible to measure NO and N2O concentration at several ppb and sub ppb level. It is very good sensitivity in comparison with other NO and N2O measurement methods like chemiluminescence (sub ppm level), SAW (ppb level) or gas chromatography (ppb level).