Inh.: Dr. Renate Gorre
D-78465 Konstanz / Germany
Fon: +49 (0)7533 97227
Fax: +49 (0)7533 97228
in Quantum Electronics
Henry Baltes, Peter Günter, Ursula Keller,
Fritz K. Kneubühl †, Walter Lukosz,
Hans Melchior, Markus W. Sigrist
Irio G. Calasso
Photoacoustic and Photothermal
Applied to Trace Gas
Detection and Molecular Dynamics.
1st edition 1999. VI, 110
pages, € 64,00.
This thesis deals with photoacoustic (PA) and photothermal (PT) studies on gas mixtures by using a continuously tunable high pressure CO2 laser and a microphone or a HeNe laser probe beam. A new theoretical approach allows a generally valid description of the gas density variation after laser pulse excitation. This model has been applied for the investigation of microphone characteristics suitable to increase the signal-to-noise ratio (SNR) in pulsed photoacoustics and for the analysis of measured PT beam deflection (PTBD) signals for the derivation of molecular relaxation rates and thermal conductivities of gases. In view of optimizing the performance for pulsed PA detection with microphones in a non-resonant cell, the dependence of the SNR on the microphone responsivity and bandwidth has been investigated for the first time both theoretically and experimentally. This permits to select the most appropriate microphone for maximum detection sensitivity. An example of a PA investigation is given for a mixture of six CO2 isotopes. This study allowed the quantitative analysis of the mixture and the determination of previously unknown absorption cross sections. Furthermore, vibrational-translational (V-T) relaxation rates are derived for various gases and gas mixtures from PTBD signal shapes. From the same signals, thermal conductivity data are deduced simultaneously.
Keywords: photoacoustic (PA) and photothermal (PT) studies, Laser Spectroscopy, Trace Gas Detection, Molecular Dynamics
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