Off-Axis Cavity Enhanced Absorption Spectroscopy Detection Techniques for the Measurement of Carbon Dioxide

The spectrum of carbon monoxide was obtained around 1. 573 mu m using a tunable distributed feedback semiconductor laser with a high-finesse cavity at room temperature via off-axis cavity enhanced absorption (CEA) spectroscopic technique. The absorption line of carbon monoxide at 6 357. 311 6 cm(-1) was chosen for trace detection. Meanwhile, in order to get more accurate measurements, absorption path length of the cavity calibration methods was studied, and a simple and practical calibration method was given. The results show that, the equivalent absorption path length of high-precision optical resonator was similar to 1 195. 73 m. At last, we got the concentration of carbon monoxide in the real atmosphere to be similar to 388. 346 ppm (S/N approximate to 22), and the detection limit of carbon monoxide was 17. 65 ppm. By combination of wavelength modulation technology and OA-CEAS technology, a minimum detectable concentration of 0. 36 ppm (S/N approximate to 1 064) was achieved eventually.