双重频率锁定的腔衰荡吸收光谱技术及信号处理  

Research and data processing of double locked cavity ringdown absorption spectroscopy

作　　者：贾梦源 赵刚[1,2] 侯佳佳[1,2] 谭巍[1,2] 邱晓东[1,2] 马维光[1,2] 张雷[1,2] 董磊[1,2] 尹王保[1,2] 肖连团[1,2] 贾锁堂[1,2] 

机构地区：[1]山西大学激光光谱研究所,量子光学与光量子器件国家重点实验室,太原030006 [2]山西大学,极端光学协同创新中心,太原030006

出　　处：《物理学报》2016年第12期336-342,共7页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2012CB921603);教育部长江学者和创新团队发展计划(批准号:IRT13076);国家自然科学基金(批准号:11434007,61475093,61378047,61275213,61475093);国家科技支撑计划(批准号:2013BAC14B01);山西省青年科学基金(批准号:2013021004-1,2012021022-1);山西省回国留学人员科研资助项目(批准号:2013-011,2013-01);山西省高等学校创新人才支持计划资助的课题~~

摘　　要：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C_2H_2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 k Hz,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4×10^(-9)cm^(-1)(2 s平均).A continuous wave cavity ringdown spectroscopy based on a double-locking loop is proposed to improve the short-coming 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 ν1＋ν3 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 e-cient 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

关 键 词：腔衰荡光谱技术 双重锁定 PDH锁频 KALMAN滤波 

分 类 号：O433[机械工程—光学工程] TN911.7[理学—光学]