Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass ce...Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv （parts-per-billion in volume）, respectively.展开更多
A real time α-β-γ filtering technique is applied to the monitoring of atmosphere CH4 based on a tunable diode laser spectrum system operating at 1.654μm. This technique is developed for improving the sensitivity a...A real time α-β-γ filtering technique is applied to the monitoring of atmosphere CH4 based on a tunable diode laser spectrum system operating at 1.654μm. This technique is developed for improving the sensitivity and precision of CH4 concentration measurement with slow concentration change. The effectiveness of this technique is evaluated by performing CH4 concentration measurement and using it to monitor the varying methane level in the atmosphere. It was proved that signal noise ratio enhancement factor is 4.25. The comparison between this filter and moving average is also included in this article. It indicates the advantage of the α-β-γ real time filter.展开更多
基金Project supported by the National Natural Science Foundation of China （Grant No 10274080） and the National High Technology Research and Development Program of China （Grant No 2003AA641010）.
文摘Tunable diode laser absorption spectroscopy （TDLAS） has been widely employed in atmospheric trace gases detection. The ratio of the second-harmonic signal to the intensity of laser beam incident to the multi-pass cell is proved to be proportional to the product of the path length and the gas concentration under any condition. A new calibration method based on this relation in TDLAS system for the measurement of trace gas concentration is proposed for the first time. The detection limit and the sensitivity of the system are below 110 and 31ppbv （parts-per-billion in volume）, respectively.
文摘基于仿真平台,搭建了TDLAS氢气检测系统,对4 712.905 cm^(-1)处的吸收光谱进行调制并利用锁相放大器提取出二次谐波信号。通过比较不同激光调制参量对二次谐波信号波形的影响进而选取最佳参数,调制幅度参量取值范围为0.1~0.35 V,观测二次谐波波形,结合波峰和波形对称性两个评估条件,确定最佳调制幅度为0.25 V。调制频率参量取值范围0.5~30 k Hz,结合二次谐波信号幅值和对噪声的抑制效果两个评估条件,选取调制频率为10 k Hz。结果表明,通过激光调制参量的优化选择可以获得更理想的二次谐波信号。该研究为开展氢气激光检测TDLAS系统调制参数的选取提供了理论依据,对改善实际应用中系统测量精度提供理论指导。
基金Project supported by the National Natural Science Foundation of China （Grant No 10274080） and the National High Technology Research and Development Program of China （Grant No 2003AA641010）.
文摘A real time α-β-γ filtering technique is applied to the monitoring of atmosphere CH4 based on a tunable diode laser spectrum system operating at 1.654μm. This technique is developed for improving the sensitivity and precision of CH4 concentration measurement with slow concentration change. The effectiveness of this technique is evaluated by performing CH4 concentration measurement and using it to monitor the varying methane level in the atmosphere. It was proved that signal noise ratio enhancement factor is 4.25. The comparison between this filter and moving average is also included in this article. It indicates the advantage of the α-β-γ real time filter.
