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Research On Tunable Diode Laser Absorption Spectroscopy Application To Gas Analysis

Posted on:2008-01-22Degree:MasterType:Thesis
Country:ChinaCandidate:X YinFull Text:PDF
GTID:2178360245992744Subject:Measurement technology and equipment
Abstract/Summary:PDF Full Text Request
Tunable diode laser absorption spectroscopy (TDLAS) is a new method to detect trace-gas qualitatively or quantificationally based on the scan characteristic of the diode laser used to obtain the characteristic absorption spectroscopy. It needs to be combined with a long absorption path in the ambient trace-gas measurements.TDLAS has significant advantages not only in the sensitivity but also in rapidity of response.It has been widely used in many atmospheric trace-gases detection, ground trace-gas detection and gas leakage detection.In this paper the fundamental principle of the TDLAS is studyed, the related spectroscopy techniques are described, such as absorption spectroscopy, wave and frequency modulation absorption spectroscopy, etc.Based on the characteristic of different types of the laser diode, considering the HITRAN database of carbon dioxide, the distributed feedback (DFB) laser diode is selected. The experiential equations of scan character tuned by current and temperature are explained and validated by testing the static characteristics of the DFB. The tuning range and ability are obtained. Comparing the two kinds of tune character, considering the characteristic of on-line gas analysis technique, the way of tuning in current is chosen.One set of experiment device has been designed and installed for the purpose of research and application of TDLAS technology combined with a long absorption path. Here carbon dioxide with different concentration has been taken as the research object. The spectrum database of carbon dioxide has been analyzed; the characteristic peaks of the spectrum have been calculated and validated by the HITRAN database; the multi-harmonic waves have been achieved and analyzed, and the second-harmonic signal is chosen, its relationship with concentration is gained, an asymmetry to its spectrum is discussed, and methods are proposed to improve it.A lot of works have to be done to meet the demand of the low concentration and high precision in gas detecting. The system improvement scheme and the next step of the experiment are introduced in the end.
Keywords/Search Tags:Tunable diode laser absorption spectroscopy, tune character, carbon dioxide, characteristic peaks, the second-harmonic signal
PDF Full Text Request
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