Cavity ring-down spectroscopy for the isotope ratio measurement of methane in ambient air with DFB diode laser near 1.65 μm

摘要

. For performing concentration measurements the sample gas was admitted to vacuum chamber. To detect a trace gas concentration, it is necessary to increase light and gas interaction time as much as possible [2]. Therefore, we used 172 cm long chamber and were able to achieve a decay time of 460 μs and a path length of 138 km. Experiments were conducted at different pressures. The experimentally measured CH4 absorbance spectra plotted versus wavenumber show a very good agreement with calculations from HITRAN database [3]. The results are presented in Fig. 1.