关键词: 光声光谱/
量子级联激光器/
一氧化二氮/
痕量气体探测
English Abstract
Detection of nitrous oxide by resonant photoacoustic spectroscopy based on mid infrared quantum cascade laser
Zhou Yu1,2,Cao Yuan1,2,
Zhu Gong-Dong1,
Liu Kun1,
Tan Tu1,
Wang Li-Jun3,
Gao Xiao-Ming1
1.Anhui Institute of Optics and Fine Mechanics, Hefei Institute of Physical Science, Chinese Academy of Sciences, Hefei 230031, China;
2.University of Science and Technology of China, Hefei 230026, China;
3.Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Fund Project:Project supported by the National Key Research and Development Program, China (Grant No. 2017YFC0209700) and the National Natural Science Foundation of China (Grant Nos. 41730103, 41475023, 41575030, 61734006).Received Date:20 December 2017
Accepted Date:08 January 2018
Published Online:20 April 2019
Abstract:Atmospheric greenhouse gases have great influence on the climate forcing, which is important to human being and also for natural systems. Nitrous oxide (N2O), such as carbon dioxide and methane, is an important greenhouse gas. It plays an important role in the atmospheric environment. Therefore, sensitive measurement of N2O concentration is of significance for studying the atmospheric environment. In this paper, a photoacoustic spectroscopy (PAS) system based on 7.6 m mid infrared quantum cascade laser combined with resonant PAS technique is established for the sensitive detection of N2O concentration. The PAS has been regarded as a highly sensitive and selective technique to measure trace gases. Compared with laser absorption spectroscopy, the PAS offers several intrinsic attractive features including ultra-compact size and no cross-response of light scattering. In addition, the signal of PAS is recorded with low-cost wavelength-independent acoustic transducer. The performance of the developed system is optimized and improved based on the traditional photoacoustic spectroscopic detection. Dual beam enhancement method is used to increase the effective optical power which effectively improves the detection sensitivity of the system. The N2O absorption line at 1307.66 cm-1 is chosen as the target line, and an operation pressure of 50 kPa is selected for reducing cross-talking from H2O absorption line. By detecting the photoacoustic signals of a certain concentration of N2O at different modulation frequencies and modulation amplitudes, the optimal modulation frequency and modulation amplitude of the system are determined to be 800 Hz and 90 mV, respectively. Different concentrations of N2O gas are detected under the optimized parameters, and calibration curve of the system, that is, the curve of photoacoustic signal versus concentration of N2O is obtained, which shows good linearity. The experimental results show that the minimum detection limit of the system is 150 ppb at a pressure of 50 kPa with an integration time of 30 ms. The system noise can be further reduced by increasing the averaging time. A minimum detection limit of 37 ppb is achieved by averaging signals 100 times, and the signal of N2O in the atmosphere is obtained.
Keywords: photoacoustic spectroscopy/
quantum cascade laser/
nitrous oxide/
trace gas detection
