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拉曼光谱是一种无损、快速的物质成分分析和检测方法.由于拉曼信号强度微弱，使得拉曼光谱的检测应用受到极大的限制.针对增强拉曼散射信号强度、提高检测灵敏度这一问题，设计了一种用于自发拉曼散射信号增强的共焦腔样品池，开展了基于该共焦腔的空气拉曼散射信号增强研究.共焦腔的腔镜反射率为92%，这一设计在保证共焦腔通带宽度与激光器线宽匹配的同时能有效地降低共振调节难度.实验中采用0o探测构型收集拉曼信号，并由成像式拉曼光谱仪获取光谱信号.实验发现，在共振状态下，共焦腔的耦合效率达到87.5%，单向激光功率实现约11倍放大；与无共振腔相比，共焦腔对拉曼信号实现17倍放大，信噪比提高2倍.此外，空气中CO2的3检测限达到200 ppm量级.结果表明，该系统对自发拉曼散射信号增强效果显著，并且有较高的检测灵敏度.Raman spectroscopy is a powerful diagnostic method for gas analysis due to its advantages like non-invasiveness and fast speed. However, its applications are greatly restricted because of the weak signal level caused by small scattering cross section. In order to enhance the Raman signal level and improve the detection sensitivity, a sample cell of confocal cavity is designed and the enhanced Raman signal of ambient air based on this cavity is demonstrated experimentally. The confocal cavity is constructed with a pair of plano-concave reflectors with a curvature radius of 150 mm and reflectivity of 92%. This low reflectivity design not only allows for bandwidth matching with the line-width of excitation laser but also makes the resonant condition satisfied easily. The measured output power of the confocal cavity is over 42 mW in resonant condition, which gives a coupling efficiency of 87.5% when divided with the input power 48 mW. The high coupling efficiency enables the output power efficiently to reach 11 times that for the intra-cavity laser power in one direction. Raman scattering of ambient air is tested to verify the performance of the confocal cavity. In our experiments, the Raman signals are collected in a forward scattering configuration by an imaging Raman spectrometer which is connected to a CCD camera. Strong Raman signals of O2 and N2, even H2O are observed with 1 s exposure time in resonant condition, and rotational lines (O-branch and S-branch) of O2 and N2 are also clearly detected when exposure time is set to be 10 s. Compared with the results obtained without confocal cavity, the Raman signal level is enhanced 17 times and the signal-to-noise ratio is improved twice. In addition, a limit of detection (3) at a magnitude of 200 ppm for CO2 in ambient air is achieved for the resonant confocal cavity. These results indicate that the system can significantly enhance the spontaneous Raman scattering signal level and improve the detection sensitivity. Furthermore, the confocal cavity is applicable to the Raman analyses of other gas samples.
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Keywords:
- resonant confocal cavity /
- Raman scattering /
- gas analysis
[1] Zhang L, Zheng H Y, Wang Y P, Ding L, Fang L 2016 Acta Phys. Sin. 65 054206 (in Chinese)[张莉, 郑海洋, 王颖萍, 丁蕾, 方黎 2016 物理学报 65 054206]
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[3] Jochum T, Fischer J C, Trumbore S, Popp J, Frosch T 2015 Anal. Chem. 87 11137
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[5] Shreve A P, Cherepy N J, Mathies R A 1992 Appl. Spectrosc. 46 707
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[7] Son H 2013 Sensors and Actuators B:Chemical 176 64
[8] Yang X, Chang A S P, Chen B, Gu C, Bondet T C 2013 Sensors and Actuators B: Chemical 176 64
[9] Guo J J, Yang D W, Liu C H 2016 Spectrosc. Spect. Anal. 36 96 (in Chinese) [郭金家, 杨德旺, 刘春昊 2016 光谱学与光谱分析 36 96]
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[11] Rupp S, Off A, Seitz-Moskaliuk H, James M T, Telle H H 2015 Sensors 15 23110
[12] Utsav K, Silver J A, Hovde D C, Varghese P L 2011 Appl. Opt. 50 4805
[13] Hill R A, Hartley D L 1974 Appl. Opt. 13 186
[14] Li X Y, Xia Y X, Zhan L, Huang J M 2008 Opt. Lett. 33 2143
[15] Yang D W, Guo J J, Du Z F, Wang Z N, Zheng R E 2015 Spectrosc. Spect. Anal. 35 645 (in Chinese) [杨德旺, 郭金家, 杜增丰, 王振南, 郑荣儿 2015 光谱学与光谱分析 35 645]
[16] Li X Y, Xia Y X, Huang J M, Zhan L 2008 Chin. Phys. Lett. 25 3326
[17] King D A, Pittaro R J 1998 Opt. Lett. 23 774
[18] Thorstensen J, Haugholt K H, Ferber A, Bakke K A H, Tschudi J 2014 J. Europ. Opt. Soc. Rap. Public. 9 14054
[19] Salter R, Chu J, Hippler M 2012 Analyst 137 4669
[20] Karpf A, Rao G N 2015 Appl. Opt. 54 6085
[21] Zuo D L, Yu A L, Li Z, Wang X B, Xiong Y H 2015 Proc. of SPIE 9611 Imaging Spectrometry XX San Diego, California, United States, August 9, 2015 96110N-19
[22] Saleh B E A, Teich M C 2007 Fundamentals of Photonics (Second Edition) (Hoboken: Wiley-Interscience)pp394395
[23] Barnes J A, Gough T E, Stoer M 1999 Rev. Sci. Instrum. 70 3515
[24] Hanf S, Keiner R, Yan D, Popp J, Frosch T 2014 Anal. Chem. 86 5278
[25] Zhang S G, Hu S X, Lin J M, Shao S S, Cao K F, Huang J, Xu Z H 2014 Infrared Laser Eng. 43 1135 (in Chinese) [张世国, 胡顺星, 林金明, 邵石生, 曹开法, 黄见, 徐之海 2014 红外与激光工程 43 1135]
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[1] Zhang L, Zheng H Y, Wang Y P, Ding L, Fang L 2016 Acta Phys. Sin. 65 054206 (in Chinese)[张莉, 郑海洋, 王颖萍, 丁蕾, 方黎 2016 物理学报 65 054206]
[2] Buldakov M A, Korolkov V A, Matrosov I I, Petrov D V, Tikhomirov A A 2013 J. Opt. Technol. 80 426
[3] Jochum T, Fischer J C, Trumbore S, Popp J, Frosch T 2015 Anal. Chem. 87 11137
[4] Schlter S, Krischke F, Popovska-Leipertz N, Seeger T, Breuer G, Jeleazcov C, Schttler J, Leipertz A 2015 J. Raman Spectrosc. 46 708
[5] Shreve A P, Cherepy N J, Mathies R A 1992 Appl. Spectrosc. 46 707
[6] Troyanova-Wood M A, Petrov G I, Yakovlev V V 2013 J. Raman Spectrosc. 44 1789
[7] Son H 2013 Sensors and Actuators B:Chemical 176 64
[8] Yang X, Chang A S P, Chen B, Gu C, Bondet T C 2013 Sensors and Actuators B: Chemical 176 64
[9] Guo J J, Yang D W, Liu C H 2016 Spectrosc. Spect. Anal. 36 96 (in Chinese) [郭金家, 杨德旺, 刘春昊 2016 光谱学与光谱分析 36 96]
[10] Yu A L, Zuo D L, Li B, Gao J, Wang X B 2016 Appl. Opt. 55 3650
[11] Rupp S, Off A, Seitz-Moskaliuk H, James M T, Telle H H 2015 Sensors 15 23110
[12] Utsav K, Silver J A, Hovde D C, Varghese P L 2011 Appl. Opt. 50 4805
[13] Hill R A, Hartley D L 1974 Appl. Opt. 13 186
[14] Li X Y, Xia Y X, Zhan L, Huang J M 2008 Opt. Lett. 33 2143
[15] Yang D W, Guo J J, Du Z F, Wang Z N, Zheng R E 2015 Spectrosc. Spect. Anal. 35 645 (in Chinese) [杨德旺, 郭金家, 杜增丰, 王振南, 郑荣儿 2015 光谱学与光谱分析 35 645]
[16] Li X Y, Xia Y X, Huang J M, Zhan L 2008 Chin. Phys. Lett. 25 3326
[17] King D A, Pittaro R J 1998 Opt. Lett. 23 774
[18] Thorstensen J, Haugholt K H, Ferber A, Bakke K A H, Tschudi J 2014 J. Europ. Opt. Soc. Rap. Public. 9 14054
[19] Salter R, Chu J, Hippler M 2012 Analyst 137 4669
[20] Karpf A, Rao G N 2015 Appl. Opt. 54 6085
[21] Zuo D L, Yu A L, Li Z, Wang X B, Xiong Y H 2015 Proc. of SPIE 9611 Imaging Spectrometry XX San Diego, California, United States, August 9, 2015 96110N-19
[22] Saleh B E A, Teich M C 2007 Fundamentals of Photonics (Second Edition) (Hoboken: Wiley-Interscience)pp394395
[23] Barnes J A, Gough T E, Stoer M 1999 Rev. Sci. Instrum. 70 3515
[24] Hanf S, Keiner R, Yan D, Popp J, Frosch T 2014 Anal. Chem. 86 5278
[25] Zhang S G, Hu S X, Lin J M, Shao S S, Cao K F, Huang J, Xu Z H 2014 Infrared Laser Eng. 43 1135 (in Chinese) [张世国, 胡顺星, 林金明, 邵石生, 曹开法, 黄见, 徐之海 2014 红外与激光工程 43 1135]
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