Abstract: The greenhouse effect has a great impact on the earth's environment and climate, so accurate detection of greenhouse gases is of great significance. As one of the important greenhouse gases, nitrous oxide (N2O) has a much higher greenhouse effect potential than carbon dioxide (CO2). However, compared to the widely studied CO2 and methane (CH4), there is less research on N2O. In this paper, a system based on a domestically developed 7.6 μm mid infrared quantum cascade laser was established for atmospheric N2O detection. The system adopts wavelength modulation and the second harmonic detection technology, with the N2O absorption line at 1307.66 cm-1 as the target line. Firstly, the optimal modulation amplitude of the system was determined by detecting the second harmonic signal of a certain concentration of N2O at different modulation amplitudes. Then under the optimal experimental conditions, N2O gas with different concentrations was measured, and the signal-volume fraction calibration curve of the system was obtained. The results showed that the minimum detection limit of N2O volume fraction of the system was 1.34 × 10-9, indicating that the system can meet the needs of atmospheric N2O measurement. A 6-hour detection of N2O was further carried out, and the averaged volume fraction of N2O during detection was 325 × 10-9, which is equivalent to the well-known volume fraction of atmospheric N2O of 320 × 10-9.

Key words: quantum cascade laser, nitrous oxide, wavelength modulation absorption spectroscopy, trace gas detection