基于OF-CEAS的亚ppb量级氨气检测OA

To enhance the sensitivity and response speed of ammonia detection using laser absorption spec-troscopy,optical feedback cavity-enhanced absorption spectroscopy(OF-CEAS)was employed.The characteristic absorption line of ammonia near 6 612.7 cm⁻¹(1 512 nm)was selected as the target transi-tion.A V-shaped optical resonant cavity composed of three high-reflectivity mirrors was constructed,with a single-arm length of 20 cm.The ring-down time of the empty cavity was measured to be 48.12 μs,cor-responding to a finesse of approximately 100 000 and an equivalent absorption path length of 14.4 km.System stability was significantly improved through precise control of temperature and gas pressure.The optical setup was housed in a temperature-controlled chamber with a stability of±0.005 ℃.In addition,a self-developed high-precision pressure control system maintained the intracavity pressure at(30 000±1.5)Pa.Under these conditions,a detection limit as low as 12 parts per trillion(ppt)was achieved at an integration time of 168 s,corresponding to a minimum detectable absorption coefficient of 1.35×10⁻¹⁰ cm⁻¹.To mitigate response delays caused by adsorption of ammonia molecules on the inner surfaces of the gas cell and pipelines,a miniaturized cavity with a volume of 7.8 mL was implemented to reduce molecular residence.Furthermore,silane passivation coatings were applied to critical pipeline sec-tions and the inner cavity surface to suppress adsorption effects,resulting in a reduction of the average sys-tem response time to 196 s.