[Measurement of oxygen concentration using multimode diode laser absorption spectroscopy].

Tunable diode laser absorption spectroscopy (TDLAS) is a widely used technique for high sensitivity, good selectivity and fast response. It is widely used in environment monitoring, industrial process control and biomedical sensing. In order to overcome the drawbacks of TDLAS including high cost, poor stability and center wavelength shift problem. A multi-mode diode laser system based on correlation spectroscopy and wavelength modulation spectroscopy (TMDL-COSPEC-WMS) was used to measure O2 concentration near 760nm at the 1%~30% range of near room temperature. During the experiment, the light is splitter into two beams, respectively through the sample and measuring cell, two receiving optical signal collection containing gas concentration information sent back stage treatment, invert the oxygen concentration through correlation and ratio between measured signal and reference signal, the correlation spectroscopy harmonic detection technique is used to improve the stability of the system and the signal to noise ratio. The result showed that, there was a good linear relationship between the measured oxygen concentration and the actual concentration value. A detection limit of 280 pmm. m in the 1 atmospheric which approved of the same sample. A continuous measurement for oxygen with the standard deviation of 0. 056% in ambient air during approximately 30 minutes confirms the stability and the capability of the system. The design of the system includes soft and hardware can meet the needs of oxygen online monitoring. The experimental device is simple and easy to use, easy to complex environment application.

[Measurements of CO2 concentration at high temperature and pressure environments using tunable diode laser absorption spectroscopy].

The present research was planned to develop a method for species concentration measurements under high temperature and pressure environments. The characteristics of CO2 spectrum at high temperature and pressure were studied at first. Based on the research above, tunable diode-laser absorption of CO2 near 2.0 microm incorporating fixed-wavelength modulation spectroscopy with second-harmonic detection was used to provide a method for sensitive and accurate measurements of gas temperature and CO2 concentration at high temperature and pressure. Measurements were performed in a well-controlled high temperature and pressure static cell. The results show that the average error of the CO2 concentration measurements at 5 atm, 500 K and 10 atm, 1000 K is 4. 49%. All measurements show the accuracy and potential utility of the method for high temperature and pressure diagnostics.

[Study on CO2 measurement using tunable multi-mode diode laser absorption spectroscopy].

Tunable diode laser absorption spectroscopy (TDLAS) technology is a kind of fast time response, large-range, continuous on-line monitoring gas detection technique. It is the mainstream technology of gas detection. In this paper the multimode laser diode was used as light source. Multi-mode laser combined with correlation spectroscopy can improve the test reliability and stability. It can also conquer the problem of the central wavelength change of the single mode diode laser due to thermal or mechanical fluctuations in durable working process. A FP laser was used as the light source in this research. A multi-mode diode laser system based on correlation spectroscopy and wavelength modulation spectroscopy (TMDL-COSPEC-WMS) was used to measure carbon dioxide in ambient air around 1 570 nm. The carbon dioxide concentrations were derived from the relationship between the normalized WMS-2f signal peak heights of the measurement and reference signals which selected based on high signal to noise ratio and correlation coefficient. All measurements were performed with controlled carbon dioxide and nitrogen mixtures in which carbon dioxide concentrations range from 0. 6% to 30%. The calculation results showed that there was a high linear relationship between the measured and actual carbon dioxide concentration, the linearity was 0. 998 7 and the fitted slope was 1. 061+/-0. 016 8 respectively over the tested range. A detection limit of 335 ppm m was achieved. The standard deviation of 0. 036 7% was achieved using 20 successive measurements with each measurement time taking approximately 10 s during 20 minutes, which demonstrated good stability of the system. Good agreements between the measurements of the system and actual values confirm the accuracy and potential utility of the system for carbon dioxide detection.