Theoretical Analysis of the Residual Amplitude Modulation of Frequency Modulation Strong Absorption Spectroscopy
ZHANG Hu1, ZHANG Yong-zhi2, YIN Zhao-xia3, WANG Xiao-bo2, MA Wei-guang2*
1. School of Computer and Information Technology of Shanxi University, Taiyuan 030006, China 2. Laser Spectroscopy Laboratory of Shanxi University, Taiyuan 030006, China 3. The Affiliated High School of Shanxi University, Taiyuan 030006, China
Abstract：The application of frequency modulation(FM) spectroscopy technology in the trace gas detection is greatly restricted by the residual amplitude modulation(RAM) which induced by the birefringence of the electro-optic modulator(EOM) and the misaligned linear polarization direction of laser to the EOM. Based on the interaction between the laser field and crystal, a lineshape expression of the FM spectroscopy with RAM is obtained. The angle between the polarization direction of input light and the principle axis of EOM, θ，the phase difference between the two principle axes of electro-optic crystal, Δ, and the modulation index FM, β, are the major factors to influence the lineshape. The larger θ and larger Δ are, the stronger distortion of the lineshape is. Meanwhile a DC offset exists in the FM dispersion spectroscopy which is influenced by θ and Δ. Finally a servo control of θ and Δ is suggested to reduce the RAM. These phenomenon and the analysis of the lineshape provide a necessary technical support for the fiber components based FM spectroscopy.
[1] ZHU Liang, YAN Long, ZOU Bing, et al(朱 亮，严 龙，邹 兵，等). Instrument Technique and Sensor(仪表技术与传感器), 2011，3: 31. [2] ZHANG Xiao-xing, YAO Yao, TANG Ju, et al(张晓星，姚 尧，唐 炬，等). High Voltage Engineering(高电压技术), 2008，34(4): 664. [3] SONG Xiao-hui, HAI Zhong-tian(宋晓辉，海中天). Measurement Technique(计量技术), 2007，29: 76. [4] DU Bin-xian, CHEN Jin-run, YIN Jun(杜彬贤，陈今润，尹 军). Chemical Engineering & Equipment(化学工程与装备), 2010，2: 64. [5] ZHANG Jing-chao, LIU Jin, WANG Yu-tian, et al(张景超，刘 瑾，王玉田，等). Journal of Optoelectronics Laser(光电子激光), 2004，15(4): 428. [6] Nagali V, Chou S I, Baer D S, et al. Appl. Opt., 1996，35(21): 4026. [7] Kluczynski P, Gustafsson J, Lindberg A M, et al. Spectrochim. Acta, Part B, 2001, 56(8): 1277. [8] Bjorklund G C, Levenson M D, Lenth W, et al. Appl. Phys. B, 1983，32(3): 145. [9] Paldus B A, Kachanov A A. Can. J. Phys., 2005，83: 975. [10] Hamilton D J, Nix M G D, Baran S G, et al. Appl. Phys. B, 2010, 100(2): 233. [11] Ye J, Ma L S, Hall J L. Opt. Lett., 1996, 21(13): 1000. [12] Foltynowicz Aleksandra, Ma Weiguang, Axner Ove. Optics Express, 2008, 16(19): 14689. [13] Bell C L, Hancock G, Peverall R, et al. Optics Express, 2009, 17(12): 9834. [14] Ma Weiguang, Foltynowicz Aleksandra, Axner Ove. Opt. Soc. Am. B, 2008, 25(7)：1144. [15] http://dip.sun.ac.za/~weideman/research/mfiles/cef.m [16] HITRAN 2004 Database (Version 12.0). [17] Wong N C, Hall J L. J. Opt. Soc. Am. B, 1985, 2：1527.
