Influence of oxygen on the resonant photoacoustic signal from methane excited at the ν3 mode

This paper shows that, when samples of methane in dry air are irradiated with an OPO tuned at the ν 3 mode at 3019 cm −1 , the photoacoustic signal is lower than in mixtures in pure nitrogen. In order to explain this change, we developed a rate-equation-based model which describes the methane excita...

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Bibliographic Details
Published in:Applied physics. B, Lasers and optics Lasers and optics, 2011, Vol.104 (4), p.983-987
Main Authors: Barreiro, N., Vallespi, A., Santiago, G., Slezak, V., Peuriot, A.
Format: Article
Language:English
Subjects:
Engineering
Lasers
Optical Devices
Optics
Photonics
Physical Chemistry
Physics
Physics and Astronomy
Quantum Optics
Online Access:Get full text
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Summary:This paper shows that, when samples of methane in dry air are irradiated with an OPO tuned at the ν 3 mode at 3019 cm −1 , the photoacoustic signal is lower than in mixtures in pure nitrogen. In order to explain this change, we developed a rate-equation-based model which describes the methane excitation and relaxation to heat by collisions with the buffer. In particular, we reduced the problem to a system of six energy levels taking into account the fast energy exchange between methane and oxygen resonant states and the slow relaxation rate of oxygen. Thus, the photoacoustic signal is calculated for methane–nitrogen and methane–air systems and a very good agreement is found with the experimental results.
ISSN:0946-2171
1432-0649
DOI:10.1007/s00340-011-4546-8