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针对传统腔衰荡光谱技术浓度获取率低, 提出基于双重锁定的连续波腔衰荡吸收光谱技术. 通过波长调制一次谐波信号将激光器的频率锁定到C2H2吸收线上, 同时使用PDH锁频技术将衰荡腔锁定到激光器上, 从而避免了测量过程中激光器的频率漂移和腔长的抖动, 使测量结果更加精确; 并且, 由于双重锁定, 单次衰荡事件的发生率, 也就是浓度信息的获取率只受衰荡时间以及重新锁定时间限制, 在本试验系统中采集速率可以达到30 kHz, 可以实现对气体浓度的快速测量. 为了提高信噪比, 采用Kalman滤波技术, 对浓度信息进行实时处理, 有效抑制了噪声, 根据阿伦方差分析, 探测灵敏度可以达到410-9 cm-1 (2 s平均).A continuous wave cavity ringdown spectroscopy based on a double-locking loop is proposed to improve the shortcoming of low acquisition rate of concentration in traditional scheme. A small portion of laser is separated to pass through a C2H2 reference cell, used to lock the laser frequency to the 1+3 band P(9)e absorption line of C2H2 at 6534.3634 cm-1 by the 1st harmonic demodulation of the frequency modulation spectroscopy. The remaining portion is incident on a high finesses cavity to observe the ringdown events. Meanwhile, the reflected light of cavity is used to extract the error signal to lock the laser based on the PDH frequency locking technique. As a consequence, the frequency drift of the laser and the jitter of the cavity length are improved, therefore a more relatively accuracy result is expected. The laser light is dual frequency modulated by a fiber coupled electro optic modulator (FEOM)in the above system. In order to optimize, to some extent, the asymmetry of the error signal caused by the residual amplitude modulation due to the inconsistency of the laser polarization direction with the extraordinary axis of the FEOM, the demodulation phase is adjusted carefully until the error signal is smoothed up and close to symmetry. Then, the effect of locking loop is examined. The frequency of laser, based on the measurement by a wavelength meter, is more stable and the relative frequency discrimination between the laser and the longitudinal mode of cavity is about 9.8 kHz. In addition, the PDH locking, ensuring the efficient coupling of the laser with the cavity, can gain a high acquisition rate of the concentration information. In order to obtain a complete ringdown event, the frequency of square wave to the fiber coupled acoustic optical modulator (FAOM) is limited to 30 kHz with the duty cycle of 85%, which is determined by the ringdown time and re-lock time. However, there exists a relatively large random noise in a series of ringdown time measurements of empty cavity, which is mainly caused by the errors of fitting and measurement. For the further improvement of the accuracy of experiment, an efficient digital filter, Kalman filter which can suppress the noise considerably at no expense of real-time capability, is used. The standard deviation of the ringdown time is reduced from 0.00333 to 0.00153. According to Allan variance analysis, the detection limit can reach 410-9 cm-1 for a 2 s integration time. Finally, the C2H2 gases with different concentrations from 100 ppb to 5 ppm are measured to demonstrate the linear response of this system.
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Keywords:
- cavity ringdown spectroscopy /
- double-locking loop /
- PDH frequency locking /
- Kalman filter
[1] Kiehl J T, Trenberth K E 1997 Surv. Geophys. 78 197
[2] Anne M A, Piliego C, Katsouras V, Blom P W M, de Leeuw D M 2014 Chem. Mater. 26 773
[3] Wang Y, Nikodem M, Zhang E, Cikach F, Barnes J, Comhair S, Dweik R A, Kao C, Wysocki G 2015 Sci. Rep. 5 9096
[4] Shao J, Gao X M, Yang Y, Huang W, Pei S X, Yuan Y Q, Zhou S K, Zhang W J 2006 Spectrosc. Spect. Anal. 26 213 (in Chinese) [邵杰, 高晓明, 杨顒, 黄伟, 裴世鑫, 袁怿谦, 周士康, 张为俊 2006 光谱学与光谱分析 26 213]
[5] Pei S X, Gao X M, Cui F P, Huang W, Yang Y, Shao J, Huang T, Zhao W X, Zhang W J 2005 Chin. J. Chem. Phys. 18 660 (in Chinese) [裴世鑫, 高晓明, 崔芬萍, 黄伟, 杨颙, 邵杰, 黄腾, 赵卫雄, 张为俊 2005 化学 18 660]
[6] Cao L, Wang C M, Chen Y Q, Yang X H 2006 Acta Phys. Sin. 55 6354 (in Chinese) [曹琳, 王春梅, 陈扬骎, 杨晓华 2006 55 6354]
[7] Wang C M, Li J, Gong T L, Chen Y Q, Yang X H 2007 Acta Opt. Sin. 27 2087 (in Chinese) [王春梅, 李炯, 龚天林, 陈扬骎, 杨晓华 2007 光学学报 27 2087]
[8] Wang D, Hu R Z, Xie P H, Qin M, Ling L Y, Duan J 2014 Spectrosc. Spect. Anal. 34 2845 (in Chinese) [王丹, 胡仁志, 谢品华, 秦敏, 凌六一, 段俊 2014 光谱学与光谱分析 34 2845]
[9] O'Keefeand A, Deacon D A G 1988 Rev. Sci. Instrum. 59 2544
[10] Romanini D, Kachanov A A, Sadeghi N, Stoeckel F 1997 Chem. Phys. Lett. 264 316
[11] Paldus B A, Harb C C, Spence T G, Wilke B, Xie J, Harris J S, Zare R N 1998 Appl. Phys. 83 3991
[12] Pan H, Cheng C F, Sun Y, Gao B, Liu A W, Hu S M 2011 Rev. Sci. Instrum. 82 103110
[13] Truong G W, Douglass S E, van Zee R D, Plusquellic D F, Hodges J T, Long D A 2013 Appl. Phys.B 7 532
[14] Cygan A, Lisak D, Maslowski P, Bielska K, Wojtewicz S, Domyslawska J, Trawinski R S, Ciurylo R, Abe H, Hodges J T 2011 Rev. Sci. Instrum. 82 063107
[15] Ma W G, Zhao G, Fu X F, Li Z X, Tan W, Dong L, Zhang L, Yin W B, Jia S T 2014 Chin. J. Lasers 41 0115002 (in Chinese) [马维光, 赵刚, 付小芳, 李志新, 谭巍, 董磊, 张雷, 尹王保, 贾锁堂 2014 中国激光 41 0115002]
[16] Leleux D P, Claps R, Chen W, Tittel F K, Harman T L 2002 Appl. Phys. B 74 85
[17] Claps R, Englich F V, Leleux D P, Richter D, Tittel F K, Curl R F 2001 Appl. Opt. 40 4387
[18] Riris H, Carlisle C B, Warren R E 1994 Appl. Opt. 33 5506
[19] Li Z, Ma W, Fu X, Tan W, Zhao G, Dong L, Zhang L, Yin W, Jia S 2013 Appl. Phys. Express 6 072402
[20] Li Z, Ma W, Fu X, Tan W, Zhao G, Dong L, Zhang L, Yin W, Jia S 2013 Opt. Express 21 17961
[21] Kosterev A A, Malinovsky A L, Tittel F K, Gmachl C, Capasso F, Sivco D L, Baillargeon J N, Hutchinson A L, Cho A Y 2011 Appl. Opt. 40 5522
[22] Chen W G, Wan F, Zou J X, Gu Z L, Zhou Q 2015 Chin. Phys. B 24 024206
[23] HITRAN 2008 Database (Version 12.0)
[24] Cheng B, Wang Z Y, Wu B, Xu A P, Wang Q Y, Xu Y F, Lin Q 2014 Chin. Phys. B 23 104222
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[1] Kiehl J T, Trenberth K E 1997 Surv. Geophys. 78 197
[2] Anne M A, Piliego C, Katsouras V, Blom P W M, de Leeuw D M 2014 Chem. Mater. 26 773
[3] Wang Y, Nikodem M, Zhang E, Cikach F, Barnes J, Comhair S, Dweik R A, Kao C, Wysocki G 2015 Sci. Rep. 5 9096
[4] Shao J, Gao X M, Yang Y, Huang W, Pei S X, Yuan Y Q, Zhou S K, Zhang W J 2006 Spectrosc. Spect. Anal. 26 213 (in Chinese) [邵杰, 高晓明, 杨顒, 黄伟, 裴世鑫, 袁怿谦, 周士康, 张为俊 2006 光谱学与光谱分析 26 213]
[5] Pei S X, Gao X M, Cui F P, Huang W, Yang Y, Shao J, Huang T, Zhao W X, Zhang W J 2005 Chin. J. Chem. Phys. 18 660 (in Chinese) [裴世鑫, 高晓明, 崔芬萍, 黄伟, 杨颙, 邵杰, 黄腾, 赵卫雄, 张为俊 2005 化学 18 660]
[6] Cao L, Wang C M, Chen Y Q, Yang X H 2006 Acta Phys. Sin. 55 6354 (in Chinese) [曹琳, 王春梅, 陈扬骎, 杨晓华 2006 55 6354]
[7] Wang C M, Li J, Gong T L, Chen Y Q, Yang X H 2007 Acta Opt. Sin. 27 2087 (in Chinese) [王春梅, 李炯, 龚天林, 陈扬骎, 杨晓华 2007 光学学报 27 2087]
[8] Wang D, Hu R Z, Xie P H, Qin M, Ling L Y, Duan J 2014 Spectrosc. Spect. Anal. 34 2845 (in Chinese) [王丹, 胡仁志, 谢品华, 秦敏, 凌六一, 段俊 2014 光谱学与光谱分析 34 2845]
[9] O'Keefeand A, Deacon D A G 1988 Rev. Sci. Instrum. 59 2544
[10] Romanini D, Kachanov A A, Sadeghi N, Stoeckel F 1997 Chem. Phys. Lett. 264 316
[11] Paldus B A, Harb C C, Spence T G, Wilke B, Xie J, Harris J S, Zare R N 1998 Appl. Phys. 83 3991
[12] Pan H, Cheng C F, Sun Y, Gao B, Liu A W, Hu S M 2011 Rev. Sci. Instrum. 82 103110
[13] Truong G W, Douglass S E, van Zee R D, Plusquellic D F, Hodges J T, Long D A 2013 Appl. Phys.B 7 532
[14] Cygan A, Lisak D, Maslowski P, Bielska K, Wojtewicz S, Domyslawska J, Trawinski R S, Ciurylo R, Abe H, Hodges J T 2011 Rev. Sci. Instrum. 82 063107
[15] Ma W G, Zhao G, Fu X F, Li Z X, Tan W, Dong L, Zhang L, Yin W B, Jia S T 2014 Chin. J. Lasers 41 0115002 (in Chinese) [马维光, 赵刚, 付小芳, 李志新, 谭巍, 董磊, 张雷, 尹王保, 贾锁堂 2014 中国激光 41 0115002]
[16] Leleux D P, Claps R, Chen W, Tittel F K, Harman T L 2002 Appl. Phys. B 74 85
[17] Claps R, Englich F V, Leleux D P, Richter D, Tittel F K, Curl R F 2001 Appl. Opt. 40 4387
[18] Riris H, Carlisle C B, Warren R E 1994 Appl. Opt. 33 5506
[19] Li Z, Ma W, Fu X, Tan W, Zhao G, Dong L, Zhang L, Yin W, Jia S 2013 Appl. Phys. Express 6 072402
[20] Li Z, Ma W, Fu X, Tan W, Zhao G, Dong L, Zhang L, Yin W, Jia S 2013 Opt. Express 21 17961
[21] Kosterev A A, Malinovsky A L, Tittel F K, Gmachl C, Capasso F, Sivco D L, Baillargeon J N, Hutchinson A L, Cho A Y 2011 Appl. Opt. 40 5522
[22] Chen W G, Wan F, Zou J X, Gu Z L, Zhou Q 2015 Chin. Phys. B 24 024206
[23] HITRAN 2008 Database (Version 12.0)
[24] Cheng B, Wang Z Y, Wu B, Xu A P, Wang Q Y, Xu Y F, Lin Q 2014 Chin. Phys. B 23 104222
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