摘要
量子级联激光器(QCL)具有出射功率高、覆盖范围宽等优点,在中红外探测领域发挥重要作用。由于激光器对外界环境变化的敏感性导致激光波长波动,在400 s的观测时间内频率漂移峰峰值高达180 MHz,在一定程度上限制了QCL激光器的性能,影响分子光谱探测的准确度。频率锁定技术作为改善激光器运行状态最有效的方法在中红外区域得到广泛应用。该研究发展了一种基于气体分子吸收的QCL激光频率锁定技术,以5.3μm QCL激光器为例,采用调制激光波长的方法将激光频率锁定于一氧化氮(NO)分子1875.8128 cm^(-1)处的吸收峰上。介绍了误差信号的产生原理,分析了使用三次谐波信号作为误差信号用于频率锁定的优越性。使用长30 cm的单通道NO吸收池得到了高信噪比(SNR)的NO吸收信号,标定了三次谐波幅值电压与激光频率的转换系数。并对锁定过程进行详细的介绍,探究了反馈控制回路中比例、积分、微分参数设置在激光锁频过程的重要性,给定了详细的锁定参数。主动干扰激光器锁定,从扰动开始至恢复稳定的时间好于40 ms,证明了该锁定系统可以抵抗外界干扰迅速响应并保持稳定。使用误差信号的波动结合电压-频率转换系数分析了频率锁定系统的稳定性,在10 ms的积分时间下频率漂移好于673 kHz,Allan方差分析结果显示,当积分时间延长至100 s时,相对频率漂移为4.5 kHz(对应稳定度为8×10^(-11)),有效提高了激光频率的长期稳定性。这种使用直接调制激光器而不需要使用外部调制器件的方法,简化了系统复杂度的同时也提升光学探测系统的探测性能。
Quantum cascade laser(QCL)plays an important role in mid-infrared detection because of the high output power and wide coverage range.However,due to the fluctuation of laser wavelength caused by the sensitivity of the laser to changes in the external environment,the peak-to-peak frequency drift is as high as 180 MHz within the observed time of 400 s,which affects the performance of the QCL to some extent and reduces the accuracy of molecular spectral detection.Frequency locking has been widely applied to the mid-infrared areas.In this paper,a QCL frequency locking system based on gas absorption was developed.Taking 5.3μm QCL as an example,the laser frequency is locked to the absorption peak of nitric oxide(NO)molecule at 1875.8128 cm^(-1) by modulating laser wavelength.The principle of error signal generation was introduced,and the advantages of using the third harmonics as an error signal for frequency locking were analyzed.The NO absorption signal with a high signal-to-noise ratio(SNR)was obtained using a NO absorption cell with a length of 30 cm.The conversion coefficient between the third harmonic voltage and the laser frequency was calibrated.The locking process was introduced in detail and explored the significance of proportional,integral,differential parameters of the feedback loop during the locking process,and the locking parameters had been given in detail.Disturbing the locking system,with the recovery time better than 40 ms demonstrate that the locking system can respond quickly and remain stable against external disturbances.In addition,the stability of the frequency locking system was also verified by the fluctuation of the error signal with the voltage-frequency conversion coefficient.A frequency drift better than 673 kHz(1σ,10 ms integration time)was achieved.The Allan variance analysis results show that when the integrated time is extended to 100 s,the frequency drift is lower than 4.5 kHz(corresponding to stability of 8×10^(-11)),effectively improving the laser frequency s long-term stability.This method of directly modulating laser frequency without an external modulator simplified the system and improved the stability of the optical detection system.
作者
王春晖
杨娜娜
方波
韦娜娜
赵卫雄
张为俊
WANG Chun-hui;YANG Na-na;FANG Bo;WEI Na-na;ZHAO Wei-xiong;ZHANG Wei-jun(School of Environmental Science and Optoelectronics Technology,University of Science and Technology of China,Hefei 230026,China;Anhui Institute of Optics and Fine Mechanics,Hefei Institutes of Physical Science,Chinese Academy of Sciences,Hefei 230031,China;Science Island Branch of Graduate School,University of Science and Technology of China,Hefei 230026,China)
出处
《光谱学与光谱分析》
SCIE
EI
CAS
CSCD
北大核心
2023年第8期2363-2368,共6页
Spectroscopy and Spectral Analysis
基金
国家自然科学基金项目(42022051,41627810)
中国科学院青年创新促进会(Y202089)
中国科学院合肥物质科学研究院院长基金项目(YZJJ202101,BJPY2019B02)资助。
关键词
量子级联激光器
中红外
频率锁定
比例、积分、微分控制
波长调制技术
Quantum cascade laser
Mid-infrared
Frequency locking
Proportional integral derivative control
Wavelength modulation
