采用Ziegler-Nichols-PID算法的激光红外多通池压强控制系统研制

为了实现CO₂气体同位素的高性能检测,研制了高精度、高稳定性的激光红外多通池压强控制系统。硬件方面,采用压强传感器连接于多通池前、后端,检测多通池内部气压,主控制器通过PWM信号,调控多通池前、后端比例阀导通状态,从而实现压强的闭环控制。软件方面,采用Ziegier-Nichols工程整定方法,完成对 P 、 I 、 D 3个参数的确定。结果表明:多通池压强为60 Torr(1 Torr=133.322 Pa)时,控制精度为±0.04 Torr。试验中,利用研制的多通池压强控制系统对13CO₂、12CO₂气体分子在4.3 μm吸收光谱进行测量。随着气体压强从0.026~0.066 atm (1 atm= 101 325 Pa),13CO₂和12CO₂气体分子吸收光谱的峰值随着压强增大而增大,吸收光谱宽度也随着压强的增大而增大。同时,利用红外气体检测系统对CO₂同位素丰度进行长达2 h的测量。CO₂同位素丰度均值为?9.081‰,测量值在?8.351‰~?9.736‰之间波动,最大偏差值为0.73‰。可以证明:该系统为红外CO₂气体同位素的高性能检测提供可靠保障。     

用于二氧化碳浓度红外检测的温度补偿研究

二氧化碳(carbon dioxide,CO₂)浓度监测是实现碳达峰、碳中和的重要基础,非分散红外(non-dispersive infrared,NDIR)检测技术作为温室气体测量领域应用最为广泛的技术之一,如何有效抑制温度漂移、确保长期监测数据的稳定性和可靠性是研究重点。实验表明,光源光功率、气体吸收线强、滤光片中心波长等容易受到环境温度影响。文中提出一种红外气体检测的温度补偿方法,研制了用于大气二氧化碳浓度红外检测的分析仪。选取以4.26μm为中心波长的CO₂气体吸收线;利用高低温试验箱,对分析仪进行温度补偿实验研究;配置标准CO₂气体浓度,对分析仪进行浓度标定实验研究。测量结果表明,红外CO₂气体分析仪浓度测量稳定,温度补偿显著,具有快速响应、应用范围广等优点。该红外CO₂气体分析仪为陆地生态系统碳收支监测等领域提供可靠数据支撑。     

基于近红外吸收光谱技术的高精度CO2检测系统的研制

为了准确测量地震断裂带溢出的痕量CO₂气体浓度,文中采用可调谐半导体激光吸收光谱(TDLAS)技术,选取波数4 978.202 cm-1作为CO₂检测系统的吸收谱线,采用有效光程为40 m的多通池,以STM32作为主控和数据处理核心器件,研制了高精度CO₂检测系统。针对系统中的探测器噪声与光学干涉条纹噪声,利用卡尔曼-小波分析算法滤波提升系统性能。实验表明,与滤波前相比,系统在50 ppmv CO₂浓度下的二次谐波信噪比提升了2.06倍。在不同CO₂浓度下(50、300、1 000、4 000、8 000 ppmv),系统误差为2.57%～2.66%。系统测量4 000 ppmv浓度下的CO2时检测精密度达到20.9 ppmv。利用Allan方差分析得出,积分时间在约61 s时对应的最低探测下限(MDL)为5.2 ppmv,实现了对CO₂气体的高精度测量。结果表明,所设计的高精度CO₂系统可以在气体检测领域为预测地震前兆提供良好前景。     

傅里叶红外系统监测大气中温室气体的污染特征

研制了一套90 m的开放光路傅里叶变换红外光谱(OP-FTIR)温室气体分析测量设备，并利用该设备开展了CO₂、CH₄和CO质量浓度的高精度检测。OP-FTIR系统反演CO₂、CH₄和CO的光谱区域分别为2102～2250 cm^-1、2920～3140 cm^-1和2172～2210 cm^-1。以采集到的中红外吸收光谱为反演基准，开展了与Picarro温室气体分析仪的对比测试。选取测量期间10 d的数据，研究了温湿度、风向风速与环境大气中CO₂、CH₄和CO质量浓度的关联度，并详细分析了污染物的日变化特征。实验结果表明：研制的OP-FTIR光谱系统监测温室气体质量浓度具有较高的可靠性；温度、相对湿度、风速和风向对当地污染物质量浓度影响显著；CO₂、CH₄和CO质量浓度的时序变化具有明显的周期性变化趋势。将CO、CH₄质量浓度分别...     

用于红外气体检测的多通池温度、压强控制系统研制

为了实现CO₂气体同位素的高性能检测,研制了高精度、高稳定性的多通池温度、压强控制系统。采用柔性PCB作为加热片包覆圆柱形多通池。考虑到温度控制系统的加热速率,外层包覆保温棉作为隔热装置,使得整个温度控制系统能实现快速加热,且能够保持温度的长时间稳定。采用铂电阻PT1000温度传感器对多通池温度进行精确采集,主控制器通过PWM信号,调控柔性PCB加热膜的发热功率,从而实现温度的闭环控制。压强控制系统方面,采用压强传感器连接于多通池前、后端,检测多通池内部气压,主控制器通过PWM信号,调控多通池前、后端比例阀导通状态,从而实现压强的闭环控制。结果表明,温度控制范围为18.48~42 ℃,温度控制精度为±0.08 ℃。多通池压强为60 Torr(1 Torr ≈ 133.322 Pa)时,控制精度为±0.04 Torr。该系统为红外CO₂气体同位素的高性能检测提供可靠保障。     

基于深度学习的嵌入式CO2浓度反演算法实现

以CO₂为主的温室气体排放使得全球变暖，严重影响生态环境，2021年习近平主席在二十国集团领导人峰会上提出“中国将力争2030年前实现碳达峰、2060年前实现碳中和”,因此精确检测CO₂气体浓度具有重要研究意义。由于CO₂气体吸收谱线的展宽受到气体压力、温度等因素影响，导致TDLAS气体检测系统测量结果误差增大，因此本文结合HITRAN数据库仿真，提出了基于BP神经网络深度学习的CO₂浓度反演算法和嵌入式实现方法，实现了对气体浓度的补偿，为嵌入式浓度反演算法设计提供理论依据。该算法可以移植到STM32F407中，经过测试，气体浓度的检测误差小，有效提升了气体检测精度，此方法同样适用于TDLAS型的其他气体检测应用场景中。     

非色散红外CO2传感器温度补偿方法研究

针对非色散红外CO₂传感器受温度影响导致测量精度低的问题,设计了单光路双通道的非色散红外CO₂传感器,提出一种BP神经网络补偿气室温度的新方法。本文分析了温度对传感器的光源、探测器以及对气体吸收系数的影响,并将BP神经网络补偿气室温度方法与其他补偿方法进行了实验对比。实验结果表明,BP神经网络补偿气室温度方法优于其他补偿方法,在测量10%～20%浓度范围内的CO₂时,最大相对误差为2.98%,重复性实验显示RSD为1.22%,为非色散红外CO₂传感器补偿温度提供借鉴意义。     

光子晶体光纤CO2气体传感器的研究

为了能高灵敏度地检测CO₂气体的体积分数,基于红外光谱吸收原理,设计了一种以9m长的空芯光子晶体光纤作为传感单元的CO₂气体传感器。利用该传感器测量了不同体积分数的CO₂在同一吸收波长下的吸收光谱图。结果表明,气体的吸收光强和气体的体积分数之间呈线性变化,与比尔-朗伯定律一致;传感器的灵敏度可达4.389×10-5W。可通过加长光子晶体光纤的长度,来增加气体吸收的有效距离,使传感系统获得较高灵敏度。     

基于TDLAS的CO2高温高压谱线参数测量研究

气体谱线参数的准确性对于应用可调谐半导体激光吸收光谱技术(TDLAS)开展燃烧流场参数的精确测量十分重要。针对目前谱线数据库参数在高温高压环境的不确定性,以主要燃烧产物CO₂作为目标气体,开展了CO₂高温高压谱线参数测量研究。设计了耐高温高压气室,在三段管式炉上搭建了一套气体谱线参数高温高压校准装置,以分布反馈式(DFB)半导体激光器作为光源,对中心频率4 988.655 cm^-1的CO₂吸收光谱进行了测量,获得了373～673 K温度范围内,1～3 atm多个压强下的纯CO₂高温高压吸收光谱,经过Voigt线型拟合等数据处理,得到了线强、自展宽系数、温度指数等谱线参数,与HITRAN2016数据库对应的参数进行对比,线强相对误差在-8.6%～-2.4%,线强不确定度约为4.1%,自展宽系数相对误差在-8.8%～2.1%,所测数据对现有的谱线数据库起到了修正和补充。     

基于深度学习算法的原位激光CO2检测系统研制

随着全球变暖日益严重，精准检测CO₂浓度具有重要的研究意义。可调谐半导体激光吸收光谱技术(TDLAS)具有高灵敏度、高分辨率等特点，被广泛应用于气体检测领域。为进一步提升TDLAS气体检测技术的检测精度，本文提出一种基于深度学习的原位激光二氧化碳检测系统。该系统采用BP神经网络算法反演CO₂浓度，补偿了温度压强对气体浓度反演的影响，提升了检测精度；采用无线通信模块，通过MQTT协议将检测的CO₂数据上传至OneNET云平台，实现了CO₂浓度的原位检测。经测试，该系统可以快速、稳定的处理数据，并且适配于其他气体检测系统。     

New short-wavelength laser emissions from optically pumped 13CD3OD

We report the discovery of 15 new laser emissions from ¹³ CD₃OD when optically pumped with a CW CO₂ laser. The wavelengths of these lines, ranging from 57.5 to 135.2 μm, are reported along with their polarization relative to the CO₂ pump laser, operating pressure and relative intensity. A three-laser heterodyne system was then used to measure the frequencies of 12 optically pumped laser emissions from this methanol isotope. These emissions range from 65.7 to 151.8 μm and are reported with fractional uncertainties up to 2·10^-7     

Observation and characterization of new FIR laser lines from formicacid

We report the observation and characterization of seven new far-infrared (FIR) laser lines from H¹²COOH and H¹³COOH in the range 232.2 to 746.6 μm optically pumped by a wide-tunability waveguide CO₂ laser. Their absorption frequency is outside of the tuning range of a conventional CO₂ pump laser     

LD泵浦的1.3at.%Er3+: CaF2中红外高功率固体激光器（特邀）

3 μm波段激光是高精度外科手术的理想光源,也可作为长波中红外光参量振荡器的有效泵浦源。LD直接泵浦Er3+掺杂晶体是获得2.7~3 μm波段中红外激光的有效技术途径,具有成本低、结构紧凑简单等优点。由于Er3+ 2.8 μm激光下能级阻塞问题,一般需要高浓度掺杂,但高浓度掺杂易引起强烈的光吸收,增强了激光晶体的热效应,从而阻碍了激光功率的提升。低声子能量的氟化钙晶体特有的萤石型结构使得三价稀土离子极易形成“团簇”,将低浓度Er3+掺杂到氟化钙晶体中即可获得高效率的中红外激光增益介质。笔者课题组使用温度梯度法成功生长了低浓度掺杂1.3at.%Er3+: CaF₂激光晶体,利用LD直接泵浦获得了2.2 W的中红外激光输出,这是目前利用LD端面泵浦同类晶体中的最高中红外激光输出功率。同时,文中还对上转换泵浦方式下该晶体的2.8 μm激光特性进行了研究。实验结果表明,低浓度掺杂的1.3at.%Er3+: CaF₂晶体是一类具有产业化前景的中红外激光材料,有望推动长波中红外激光器向着结构紧凑、成本低的方向发展。     

Characterization of new FIR laser lines from CD3-rockingand asymmetric CD3 deformation modes of 13CD3OD

In this paper, we report new optically pumped far-infrared (FIR) laser lines from the in-plane CD₃-rocking and asymmetric CD ₃ deformation absorption vibrational bands of ¹³CD ₃OD. A waveguide CO₂ laser of wide tunability (290 MHz) was used as the pump source, and a Fabry-Perot open cavity as the FIR laser resonator. Optoacoustic absorption spectrum was used as a guide to search for new FIR laser lines. We could observe 13 new laser lines in the range 103-491 μm. The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred lamb-dip technique was used to measure the frequency absorption transition for both new and previously reported laser lines     

First demonstration of room temperature intersubband-interbanddouble-resonance spectroscopy of GaAs/AlGaAs quantum wells

Intersubband-interband double-resonance experiments in undoped GaAs/Al_0.33Ga_0.67As multiple quantum well (MQW) structures at room temperature are discussed. The well width is 78 Å. A Ti:sapphire laser is used to pump the interband transitions, while the first intersubband transition is probed with a CO₂ laser. The intersubband absorption is found to peak at 10.6 μm, and a 10-meV linewidth is measured. The absorption signal is also recorded at a fixed CO₂ tuning while varying the pump laser wavelength from 700 to 850 nm. A high-resolution spectrum is obtained, reflecting the steplike density of states with sharp peaks at the exciton resonances     

New FIR laser lines from fully deuterated dichloromethane:completion of perpendicular/parallel emission pairs

We report 16 new far-infrared (FIR) laser emissions of CD₂ Cl₂. These lines are obtained by optically pumping the active molecule by means of a large-tunability waveguide CO₂ laser. Our tunability of 290 MHz around each CO₂ laser emission allows for the excitation of large-offset absorption transitions of CD₂Cl₂, not reachable by conventional CO₂ Lasers. While the overwhelming majority of the known FIR laser emissions of CD₂Cl₂ are polarized parallel to the polarization of the pump CO₂ line, 13 of the 16 new lines reported in this paper are polarized perpendicularly to the corresponding CO₂ pump line. The presence of both perpendicular and parallel lines is extremely important for the assignment of laser transitions     

Accurate gas diagnostics for sealed-off CO2 lasers usingnear-infrared DFB semiconductor lasers

The selective spectroscopic detection of CO₂ and H₂O in the gas mixture of a 400-W sealed-off CO₂ slab laser is reported. The detection is based on the acquisition of absorption Voigt profiles of two vibrational overtone transitions of CO ₂ and H₂O, obtained using two InGaAsP distributed feedback (DFB) semiconductor lasers. This spectroscopic method enables a direct absolute measurement of the temporal evolution for the concentrations inside the laser active volume. Monitoring takes place during laser operation without gas extraction. The experiments carried out on CO₂ and H₂O abundances confirm the paramount importance of wall desorbance phenomena in all-metal radio frequency (RF) excited lasers     

Small-frequency-difference stabilization of laser diodes using12C2H2 and 13C2H2 absorption lines for transmitter and local oscillator ofoptical heterodyne systems

Small-frequency-difference stabilization of distributed Bragg reflector (DBR) laser diodes has been demonstrated for the first time by using vibrational-rotational absorption of ¹²C₂H ₂ and ¹³C₂H₂ molecules. Frequency stabilization of two DBR laser diodes has been carried out at a wavelength of about 1.536 μm. The frequency difference between the two stabilized lasers was evaluated to be 9 GHz by the beat spectrum measurement. The experimental results suggest that such a pair of frequency-stabilized laser diodes with a small frequency difference could be used as the transmitter and local oscillator of optical heterodyne systems