摘要
针对激光传输实验中传输内通道空间狭小、CO_(2)浓度低的特点,结合波长调制TDLAS技术,设计了基于现场可编程逻辑门阵列(FPGA)的数字锁相放大器,实现锁相放大和数据采集功能一体化,并将其成功应用于低浓度CO_(2)检测中。为解决低浓度CO_(2)吸收微弱、噪声强等问题,设计了高精度ADC模块,电压分辨率可达0.3 mV;基于DDS原理内部产生正余弦参考信号,保证谐波信号单一性,且实现参考信号频率可调节,覆盖范围1~40 kHz;改进了CIC滤波器,并通过降采样级联FIR滤波器的方式,以较少的硬件资源消耗实现窄带低通滤波,积分时间200μs~20 ms可调;基于CORDIC算法实现平方和开根运算,相较于JPL算法精度更高。为系统更加小型化,基于Qt实现上位机并结合串口通信,使锁相放大器兼具数据采集处理功能。常温常压光程30 m条件下,测量了CO_(2)在2μm波段的吸收光谱,获得波长调制吸收光谱信噪比为102.6,相较于直接吸收信噪比8.8,提高约11.7倍;设计并开展低浓度CO_(2)标定实验,获取二次谐波信号幅值和CO_(2)浓度之间的线性关系,相关度为0.996;在纯氮气条件下,利用Allan方差评估了系统性能,平均时间为2 s时,系统检测下限1.30 ppm(1 ppm=10−6),平均时间为180 s时,系统检测下限0.19 ppm;分析了系统响应时间,可在0.5 s内获取气体浓度。实验结果表明,设计的数字锁相放大器具有测量灵敏度高、参数可调节、能够实时处理和小型化的特点,可满足传输内通道中低浓度CO_(2)的检测需求。
Objective The effect of thermal blooming in the laser propagation experiment is an important factor affecting the propagation evaluation.The thermal blooming is due to the absorption of gas,which causes the local air to be heated,causing the air to form a density gradient,resulting in refraction and scattering during laser transmission,thus causing the distortion of the laser spot and affecting the experimental results.In the inner channel of the laser propagation,because the laser energy density is high and the air velocity is slow,the thermal blooming is more obvious.Even the trace greenhouse gases will affect the laser propagation.CO_(2)is the greenhouse gases of highest concentration and the most difficult to completely remove in the inner channel of laser propagation.Therefore,high-precision detection of CO_(2)in the propagation channel is of great significance for propagation evaluation.The inner channel of the laser propagation is characterized by small space and low CO_(2)concentration,so a miniaturized and highly sensitive detection system is required.Wavelength Modulation-Tunable Diode Laser Absorption Spectroscopy(WM-TDLAS)technology as an effective detection method is widely used in the detection of trace gas.However,WM-TDLAS system has complex structure and large volume.Therefore,the lock-in amplifier as the core device of WM-TDLAS system is studied in this paper to meet the requirements of high-precision detection of CO_(2)and make the WM-TDLAS system more miniaturized.Methods The principle of wavelength modulation detection and lock-in amplifier deeply is analyzed,and the key technologies of digital lock-in amplifier are optimized.The reference signal is generated internally based on DDS principle,and the frequency of sine and cosine reference signal is designed to be adjustable which can expand the scope of application(Fig.2).Combined with the characteristics of wavelength modulation,the integral length of CIC filter is improved based on the number of periodic data points of the modulated signal,a
作者
张雷雷
曹振松
钟磬
黄印博
袁子豪
黄俊
齐刚
潘文雪
卢兴吉
Zhang Leilei;Cao Zhensong;Zhong Qing;Huang Yinbo;Yuan Zihao;Huang Jun;Qi Gang;Pan Wenxue;Lu Xingji(Key Laboratory of Atmospheric Optics,Anhui Institute of Optics and Fine Mechanics,HFIPS,Chinese Academy of Sciences,Hefei 230031,China;Science Island Branch of Graduate School,University of Science and Technology of China,Hefei 230026,China;Advanced Laser Technology Laboratory of Anhui Province,Hefei 230037,China;Military Representative Office in Mianyang of Space System Department,Mianyang 621000,China)
出处
《红外与激光工程》
EI
CSCD
北大核心
2023年第10期127-138,共12页
Infrared and Laser Engineering
基金
国家自然科学基金项目(42027804)
先进激光技术安徽省实验室青年基金项目(AHL2021QN01)。
