Multi-component and multi-point trace gas sensing in the wavelength modulation spectroscopy is demonstrated based on the frequency-division multiplexing and time-division multiplexing technology.A reference photodetec...Multi-component and multi-point trace gas sensing in the wavelength modulation spectroscopy is demonstrated based on the frequency-division multiplexing and time-division multiplexing technology.A reference photodetector is connected in series with a reference gas cell with the constant concentration to measure the second-harmonics peak of the components for wavelength stabilization in real time.The central wavelengths of the distributed feedback lasers are locked to the target gas absorption centers by the reference second-harmonics signal using a digital proportional-integral-derivative controller.The distributed feedback lasers with different wavelengths and modulation frequencies are injected into the gas cell to achieve multi-components gas measurement by the frequency-division multiplexing technology.In addition,multi-point trace gas sensing is achieved by the time-division multiplexing technology using a photoswitch and a relay unit.We use this scheme to detect methane(CH4)at 1650.9 nm and water vapor(H2O)at 1368.597 nm as a proof of principle with the gas cell path length of 10 cm.The minimum detection limits achieved for H2O and CH4 are 1.13 ppm and 11.85 ppm respectively,with three-point gas cell measurement;thus 10.5-fold and 10.1-fold improvements are achieved in comparison with the traditional wavelength modulation spectroscopy.Meanwhile,their excellent R-square values reach 0.9983 and 0.99564 for the concentration ranges of 500 ppm to 2000 ppm and 800 ppm to 2700 ppm,respectively.展开更多
A simple and effective wavelength calibration scheme is proposed in a quartz enhanced photoacoustic spectroscopy （QEPAS） system for trace gas detection. A reference gas cell is connected an InGaAs photodetector for ...A simple and effective wavelength calibration scheme is proposed in a quartz enhanced photoacoustic spectroscopy （QEPAS） system for trace gas detection. A reference gas cell is connected an InGaAs photodetector for detecting the absorption intensity peak caused by the gas to calibrate the gas absorption center using distributed feedback laser diode （DFB-LD） with sawtooth wave driver current. The gas absorption wavelength calibration and gas sensing operations are conducted at a special internal to eliminate the wavelength shift of DFB-LD caused by the ambient fluctuations. Compared with the conventional wavelength modulation spectroscopy （WMS）, this method uses a lower lock-in amplifier bandwidth and averaging algorithm to improve signal noise ratio （SNR）. Water vapor is chosen as a sample gas to evaluate its performance. In the experiments, the impact of sawtooth wave frequency and lock-in amplifier bandwidth on the harmonic signal is analyzed, and the wavelength-calibration technique-based system achieves a minimum detection limit （MDL） of 790ppbv and SNR with 13.4 improvement factor compared with the conventional WMS system.展开更多
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 61405105 ＆ 61475085）, the Shandong Provincial Natural Science Foundation, China （Grant No. ZR2014FQ015）, Science and Technology Development Project of Shandong Province （Grant No. 2014GGX101007）, and the Fundamental Research Funds of Shandong University （Grant Nos. 2014HW016 ＆ 2014YQ011）.
基金This work was supported by the Research Fund for the Doctoral Program of Liao Cheng University(Grant No.318051543)and the National Natural Science Foundation of China(Grant No.61475085).
文摘Multi-component and multi-point trace gas sensing in the wavelength modulation spectroscopy is demonstrated based on the frequency-division multiplexing and time-division multiplexing technology.A reference photodetector is connected in series with a reference gas cell with the constant concentration to measure the second-harmonics peak of the components for wavelength stabilization in real time.The central wavelengths of the distributed feedback lasers are locked to the target gas absorption centers by the reference second-harmonics signal using a digital proportional-integral-derivative controller.The distributed feedback lasers with different wavelengths and modulation frequencies are injected into the gas cell to achieve multi-components gas measurement by the frequency-division multiplexing technology.In addition,multi-point trace gas sensing is achieved by the time-division multiplexing technology using a photoswitch and a relay unit.We use this scheme to detect methane(CH4)at 1650.9 nm and water vapor(H2O)at 1368.597 nm as a proof of principle with the gas cell path length of 10 cm.The minimum detection limits achieved for H2O and CH4 are 1.13 ppm and 11.85 ppm respectively,with three-point gas cell measurement;thus 10.5-fold and 10.1-fold improvements are achieved in comparison with the traditional wavelength modulation spectroscopy.Meanwhile,their excellent R-square values reach 0.9983 and 0.99564 for the concentration ranges of 500 ppm to 2000 ppm and 800 ppm to 2700 ppm,respectively.
基金This work was supported by Research Fund for the Doctoral Program of Liaocheng University （Grant No. 318051543） and the National Natural Science Foundation of China （Grant No. 61475085）.
文摘A simple and effective wavelength calibration scheme is proposed in a quartz enhanced photoacoustic spectroscopy （QEPAS） system for trace gas detection. A reference gas cell is connected an InGaAs photodetector for detecting the absorption intensity peak caused by the gas to calibrate the gas absorption center using distributed feedback laser diode （DFB-LD） with sawtooth wave driver current. The gas absorption wavelength calibration and gas sensing operations are conducted at a special internal to eliminate the wavelength shift of DFB-LD caused by the ambient fluctuations. Compared with the conventional wavelength modulation spectroscopy （WMS）, this method uses a lower lock-in amplifier bandwidth and averaging algorithm to improve signal noise ratio （SNR）. Water vapor is chosen as a sample gas to evaluate its performance. In the experiments, the impact of sawtooth wave frequency and lock-in amplifier bandwidth on the harmonic signal is analyzed, and the wavelength-calibration technique-based system achieves a minimum detection limit （MDL） of 790ppbv and SNR with 13.4 improvement factor compared with the conventional WMS system.
