The study of the concentration of carbon monoxide measured based on 1.58um tunable semiconductor laser

By use of 1.58 um tunable semiconductor laser, in which its wavelength is nicely a window of communication in long wavelength band of the fiber, the measurement optical paths can well be integrated in fiber system with fiber and passive component in the fiber communication and is put to industry field. Moreover, the 1.58 um spectrum line is an absorption peak of carbon monoxide and around the spectrum line, the background gas in atmosphere has a good transmission window. It is very well to measure carbon monoxide concentration. Through measuring peaks of the second harmonic and fourth harmonic of absorption spectrum lines of carbon monoxide with TDLAS absorption spectroscopy technique, the carbon monoxide concentration can accurately be calculated by composition algebra of the second and the fourth harmonic intensities. One of the advantages of the concentration measured by the high order harmonic intensity is that it can overcome the disturbance of the low order harmonics, especially, the disturbance of laser modulation current and one harmonic. The another is that the concentration measurement has nothing to do with the laser modulation ratio and laser parameters so that it overcomes the affect of changes of the modulation intensity and laser current in measurement process and the concentration express only have relations with characteristic parameters of temperature and pressure in the measurement gas chamber and measurement intensities of the second and the fourth harmonics. Moreover, the relative measurement error of carbon monoxide concentration has nothing to do with the frequency change caused by the current of laser diode modulation. The results showed that the relative intensities of the second harmonic and fourth harmonics of the specific absorption spectra line are used to calculate gas concentrations is e