基于量子级联激光器和长光程气室的甲烷传感器

根据中红外光谱吸收原理,利用甲烷(CH₄)气体分子在7.5 μm处的基频吸收特性,设计了一种基于量子级联激光器(QCL)和新型多反射长光程气体吸收气室(MPC)的甲烷气体传感器。该仪器使用了可进行热电冷却、工作在脉冲方式下、中心波长为7.5 μm的QCL,通过在室温条件下调节其注入电流(500 mA～1.6 A调节范围),其出射光波长可以扫过CH₄(1 332.8 cm-1)气体吸收线。同时使用了一种紧凑型MPC(40 cm长,800 mL采样容积),使得系统有效总光程达到16 m。此外,系统中使用了参考气室,并加入了空间滤波光学结构以满足MPC对入射光束的要求,配合差分吸收光谱检测原理,有效地改善了光束质量,降低了由光源波动引起的噪声,提高了仪器的检测灵敏度。通过对不同浓度的甲烷气体进行多次检测,该仪器的稳定性能良好,按信噪比为1计算,可实现对甲烷气体的检测下限为1 μmol·mol-1。     

采用4.8μm中红外量子级联激光器的痕量一氧化碳气体检测仪

一氧化碳是一种无色、无味、有毒、易燃的危险气体,且低浓度的该气体可以使人中毒、窒息、危及生命。因此研制一种能够检测一氧化碳气体浓度的检测仪意义重大,尤其在环境复杂(湿度和粉尘浓度都很大)的矿井下。本文所述的是一种紧凑型检测仪器,其能够灵敏、快速、连续地监测环境空气中痕量一氧化碳气体浓度。该仪器采用激发波长为4.8μm的中红外量子级联激光器(QCL)和红外碲镉汞探测器的最新半导体技术,结合中红外光程长度为76m的多次反射herriott吸收气室,可以在4s的采样时间内实现40nmol·mol-1气体检测灵敏度。同时,该仪器利用差分吸收光谱检测原理,设计了双光路双通道空间光学结构,消除了电调制光源所带来的不稳定性,有效地提高了仪器浓度检测下限。实验表明,该仪器通过所集成的气体浓度反演算法,能够在无需校准的情况下,可以用于环境监测中的实地痕量气体测量,并且操作人员可以通过替换在不同波长下运行的QCL来测量其他气体。     

采用7.5 μm中红外量子级联激光器的痕量甲烷气体检测仪

一种具有高稳定性和高敏感度的紧凑型仪器,能精确、实时、实地连续测量和显示环境空气中的痕量甲烷(CH₄)浓度。仪器采用了已集成热电制冷器激射波长为7.5μm的法布里-珀罗量子级联激光器(QCL)在室温脉冲工作模式下的最新技术,以覆盖CH₄位于ν₄附近基频特征吸收谱带。同时,采用高品质液氮制冷碲镉汞中红外探测器,配合全反射镀金椭球反射镜一同使用,在20 cm单路径开放式光路吸收气室环境下,确保被测甲烷气体浓度为200 μmol·mol-1的实验条件下保持稳定度高达5.2×10-3。此仪器所集成的软件算法通过时间鉴别电子技术实现对QCL控制,能够在无需校准的情况下,提供连续痕量甲烷气体检测。实验表明,仪器可以用于环境监测中的实地痕量气体测量,并且操作人员可以通过替换在不同波长下运行的QCL来测量其他气体。     

基于中红外光谱吸收技术的一氧化碳气体检测系统

基于中红外光谱吸收技术,利用一氧化碳(CO)气体分子在4.6 μm处的基频吸收带,采用新脉冲的红外光源和双通道的热释电探测器,研制了一种CO浓度检测系统。该系统主要由脉冲调制式宽带热光源、开放式椭球聚光镜/气室、双通道探测器、主控及信号处理模块构成。通过优化开放式椭球聚光镜/气室,气体吸收光程达到40 cm, 探测器输出电信号的幅度增加约为原来的2~3倍。因此,采用椭球聚光镜后,将在一定程度上提高系统的信噪比从而改善系统的性能指标。利用配备的CO气体样品,研究了该系统对CO气体的传感特性。实验结果显示,该系统的最小检测下限为10 ppm,在该浓度点的测量误差约为14%;在20~25 000 ppm范围内的测量误差小于7.8%;对0 ppm气体样品的连续50分钟测量结果的最大偏差约为3 ppm,标准差约为0.18 ppm。同基于量子级联激光器和分布反馈激光器的CO检测系统相比,该系统具有性价比高、光路结构简单等优势,从而在煤矿、环保等场合下的CO检测方面具有较好应用前景。     

基于TDLAS-WMS的中红外痕量CH_4检测仪

为了对痕量甲烷(CH4)进行非接触式检测,采用可调谐二极管激光吸收光谱(TDLAS)与波长调制光谱(WMS)的检测技术,利用CH4位于中红外波段1 332.8cm-1吸收谱线,设计并研制出痕量CH4检测仪。该仪器使用中心波长为7.5μm的中红外量子级联激光器(QCL),通过调谐系数-0.2cm-1·A-1,采用固定工作温度调节其注入电流(0.6~1.6 A)的方式使其发光光谱扫描CH4气体吸收谱线(1 332.8cm-1)。在光学结构方面,该仪器采用光程为76m的herriott长光程密闭气体吸收气室,配合差分检测光路,降低了由激光光源波动引起的噪声,确保对痕量CH4进行检测。实验中,实现了40×10-9最低检测下限,检测结果的相对误差为0.09%,稳定度优于2.8%,验证了该仪器的可行性。     

中红外痕量乙烷传感器设计与稳定性分析

根据乙烷气体分子在3.3 μm处的基频吸收特性,使用中心波长为3.337 μm室温连续带间级联激光器(ICL)和有效光程为54.6 m密集光斑多通气体吸收气室(600 mL)研制了基于波长调制光谱技术(WMS)的乙烷传感器。详细介绍了基于WMS和二次谐波(2f)探测技术的光谱吸收法气体检测原理,给出了目标乙烷气体吸收线的遴选细节。此项技术的使用减小了光功率漂移对系统的影响,使得系统最低检测下限(MDL)和稳定性能得到提升。结合原理框图,通过光学和电学两个模块分别详细介绍了乙烷传感系统设计方案,描述了自主研制的软、硬件单元和商用仪器的使用及其型号供他人参考,并给出传感器光学配置实物图。而且,为匹配激光波长调制与基于压力的吸收线宽,对气压和调制深度进行优化,研究了调制幅度对应2f信号峰值及调制幅度与调制深度的关系,最终确定最优气压和调制深度分别为100 Torr和0.074 cm-1,对应的调制信号幅度为~0.026 V。此外,基于优化后的气压和调制深度,使用136.8 nmol·mol-1 乙烷标准气体进行了系统灵敏度估算。详细介绍了ICL扫描调制信号、锁相放大及数据采集单元的参数设置,并给出示波器记录的扫描调制信号及2f信号波形图片。通过对比DAQ采集的2f信号和背景噪声信号,估算系统最低检测下限为33 nmol·mol-1。最后,使用9个不同浓度乙烷标准气体(20～400 nmol·mol-1)分别进行~5 min系统标定测试,并列出了拟合曲线和拟合相关度等信息。而且,使用浓度为48 nmol·mol-1乙烷气体样品开展连续2 h系统稳定性测试并进行Allan-Werle 方差分析。结果显示,该系统工作稳定,积分时间为4 s时,乙烷气体检测灵敏度为~0.81 nmol·mol-1。通过增加系统积分时间至63 s,系统灵敏度可被提高至~0.36 nmol·mol-1。     

基于中红外痕量甲烷检测的地震预警仪

随着地震断裂带气体观测技术的快速发展,为了对地震进行精确的预报,减少因地震给人民群众生命和财产带来的损失,根据甲烷气体的释放与地震前上地壳岩石的微裂隙有直接关系的这一微观变化,设计并研制中红外痕量甲烷气体检测仪。仪器采用激发波长为7.65 μm的量子级联激光器(QCL),结合双光路长度为76 m的多次反射herriott长光程气体吸收池,可以在4 s的采样时间内实现40 nmol·mol-1气体检测灵敏度。同时,采用半导体激光器频率调制直接光谱吸收技术,降低了该仪器噪声的主要来源1/f噪声,使气体检测下限达到5 nmol·mol-1 (40 s采用时间)。在野外实验中,利用可控震源车作为模拟地震源,将6个痕量甲烷检测仪以100 m为距离等间隔放置,对距震源中心不同距离下的地表面甲烷气体浓度进行动态测量。实验表明,该仪器可以监测地震前地下痕量甲烷气体的释放,为地震前兆预警提供新的途径。     

基于中红外QCL激光和新型多通池高灵敏度测量CO和N_2O的研究

利用量子级联激光器(QCL)结合新型小型化光学多通吸收池高灵敏度同时测量CO和N2O痕量气体。所用激光为工作在4.3 mm附近的宽调谐、无跳模外腔量子级联激光器,激光在较短的时间内(1 s)连续波长扫描,并覆盖N2O(2203.73333 cm-1)和CO(2203.161 cm-1)两种分子的吸收谱线,从而实现对N2O和CO的同时测量。利用物理基长为12 cm的新型小型化光学多通吸收池,探测光在吸收池内来回反射243次,有效光程达到29 m。利用波长调制吸收光谱和二次谐波探测技术实现了对N2O和CO的高灵敏度探测,测量系统的最低可探测浓度极限约为2.0×10-9(N2O)和1.7×10-9(CO)。     

中红外量子级联激光气体检测系统

为了满足基于室温连续量子级联激光器(QCL)的中红外气体检测系统的需求,研制了板级量子级联激光器的驱动电路以及谐波锁相放大电路。通过信号发生电路产生高精度的直流偏置信号、低频锯齿波扫描信号和高频正弦波调制信号,控制激光器的工作电流,进而扫描/调制激光器的输出波长;为了探测痕量气体吸收光谱的二次谐波信号,并获得较高的信噪比,研制了锁相放大电路,主要包括倍频电路、正交转换电路和数据转换电路;为了提高系统的稳定性和可靠性,研制了高稳定性的线性供电电路以及保护电路.采用中科院半导体所研制的波长为4.76μm的QCL作为光源,开展了电学系统的功能验证实验以及气体检测实验.实验结果表明:QCL驱动电路线性度为0.006 3%,长期电流稳定度为5.0×10~(-5),QCL光强稳定度为5.07×10~(-4);锁相放大器系统具有较高的稳定性和较低的误差,一次谐波的最大误差在2.4%以内,二次谐波的最大误差在5.5%以内.通过动态配气方式开展了低浓度一氧化碳(CO)气体检测实验,在0~100×10~(-6)范围内,二次谐波信号的幅值与CO气体浓度具有较高的线性度(拟合优度0.99),表明所研制的电学系统具有良好的稳定性和可靠性,为中红外CO气体的检测提供了安全可靠的保障.     

采用长光程差分吸收光谱技术(LP-DOAS)的中红外痕量一氧化碳检测仪

一氧化碳作为一种危险的开采排放气体,在复杂的井下环境中极易累积,对矿工生命安全造成严重威胁。介绍了一种紧凑型一氧化碳检测仪,该仪器采用激发波长为4.65μm的量子级联激光器作为光源,配合中红外碲镉汞光电探测器与光程长度12m的紧凑型多次反射气室,实现了对痕量一氧化碳气体的检测。自主设计的新型高速光电信号采集系统解决了应用商业示波器造成的信号链阻抗失配的问题。这一新系统的采样带宽为400MHz,采样频率1GSPS,垂直分辨率达到12bit,有效的提高了检测仪的灵敏度与集成度。该仪器采用长光程差分吸收光谱法,通过比较实测光谱与进行Voigt展宽的理论光谱之间的残差得出此检测仪的检测下限为108×10-9。检测仪的测量误差有非平稳,慢时变的特点。根据这一特点我们采用阿伦方差对气体检测仪检测灵敏度进行了估计,经过约40s方差曲线达到极小值,此时阿伦方差值为61×10-9。在2h的稳定性测试中,检测仪稳定度达到2.1×10-3,在长达12h的稳定性测试中,检测仪的稳定度依然可以达到1.7×10-2。此仪器具有较高的灵活性,通过更换不同激射波长的激光器可以实现对多种气体的痕量检测。     

Single-QCL-based absorption sensor for simultaneous trace-gas detection of CH4 and N2O

A quantum cascade laser (QCL)-based absorption sensor for the simultaneous dual-species monitoring of CH₄ and N₂O was developed using a novel compact multipass gas cell (MGC). This sensor uses a thermoelectrically cooled, continuous wave, distributed feedback QCL operating at ~7.8 µm. The QCL wavelength was scanned over two neighboring CH₄ (1275.04 cm^?1) and N₂O (1274.61 cm^?1) lines at a 1 Hz repetition rate. Wavelength modulation spectroscopy (f = 10 kHz) with second harmonic (2f) detection was performed to enhance the signal-to-noise ratio. An ultra-compact MGC (16.9 cm long and a 225 ml sampling volume) was utilized to achieve an effective optical path length of 57.6 m. With such a sensor configuration, a detection limit of 5.9 ppb for CH₄ and 2.6 ppb for N₂O was achieved, respectively, at 1-s averaging time.     

基于单个量子级联激光器的大气多组分测量方法

利用单个新型中红外量子级联激光器作为激光光源,结合长程光学吸收池技术开展了大气多组分同时测量方法的研究.通过结合基于自适应性Savitzky-Golay滤波的数据处理算法,有效地提高了系统检测灵敏度和光谱分辨率.研究结果表明,在1 s的时间分辨率和1 atm压力条件下,采用二次微分探测技术可实现CO,N_2O和H_2O测量精度分别为8.20 ppb,7.90 ppb和64.00 ppm(1 ppb=10~(-9),1 ppm=10~(-6));通过提高信号平均时间,在最佳的积分时间(85 s)时,系统可实现的最小检测限分别为1.25 ppb(CO),1.15 ppb(N_2O)和35.77 ppm(H_2O).整个系统具有结构紧凑,成本相对较低,通过选择其他波段的量子级联激光器的激光光源,即可实现对其他分子的实时分析.本系统可广泛应用于大气化学等领域的应用研究.     

A mid-infrared scanned-wavelength laser absorption sensor for carbon monoxide and temperature measurements from 900 to 4000 K

Mid-infrared laser absorption sensors based on quantum cascade laser (QCL) technology offer the potential for high-sensitivity, selective, and high-speed measurements of temperature and concentration for species of interest in high-temperature environments, such as those found in combustion devices. A new mid-infrared QCL absorption sensor for carbon monoxide and temperature measurements has been developed near the intensity peak of the CO fundamental band at 4.6 μm, providing orders-of-magnitude greater sensitivity than the overtone bands accessible with telecommunications lasers. The sensor is capable of probing the R(9), R(10), R(17), and R(18) transitions of the CO fundamental ro-vibrational band which are located at frequencies where H₂O and CO₂ spectral interference is minimal. Temperature measurements are made via scanned-wavelength two-line ratio techniques using either the R(9) and R(17) or the R(10) and R(18) line pairs. The high-speed (1–2 kHz) scanned-wavelength sensor is demonstrated in room-temperature gas cell measurements of CO and, to demonstrate the potential of the sensor for high-temperature thermometry, in shock-heated gases containing CO for a very wide range of temperature (950–3500 K) near 1 atm. To our knowledge, these measurements represent the first use of QCL-based absorption sensor for thermometry at elevated combustion-like temperatures. The high-temperature measurements of CO mole fraction and temperature agree with the post-reflected-shock conditions within ±1.5% and ±1.2% (1σ deviation), respectively.     

Spectroscopy system based on a single quantum cascade laser for simultaneous detection of CO and CO_2

A quantum cascade laser(QCL) based system for simultaneous detection of CO and CO_2 is developed.The QCL can scan over two neighboring CO(2055.40 cm~(-1)) and CO_2(2055.16 cm~(-1)) lines with a single current scan.The wavelength modulation spectroscopy( f = 20 k Hz) is utilized to enhance the signal-to-noise ratio.A white cell with an effective optical path length of 74 m is used.The calibration of the sensor is performed and minimum detection limits of 1.3 ppb(1 × 10~(-9))for CO and 0.44 ppm(1 × 10~(-6)) for CO_2 are achieved.     

基于中红外量子级联激光器和石英增强光声光谱的CO超高灵敏度检测研究

采用石英增强光声光谱(QEPAS)技术对CO痕量气体展开检测研究. 为了实现超高灵敏度探测, 采用输出波长为4.6 μm的新颖中红外高功率分布反馈量子级联激光器为光源, 实现了对CO气体基频吸收带的激发与测量. 在优化了调制深度、气体压强和提高了CO分子的振动-转动弛豫速率后, 获得了1.95 ppbv的优异探测极限. 在分析检测结果的过程中, 讨论了能级寿命对信号强度的影响, 并对QEPAS信号强度的表达式进行了修正.     

Real-time monitoring of nitric oxide in diesel exhaust gas by mid-infrared cavity ring-down spectroscopy

We report the accurate and precise measurement of nitric oxide (NO) in automotive exhaust gas by cavity ring-down spectroscopy (CRDS) using a thermoelectrically cooled, pulsed quantum cascade laser (QCL) as a light source. A mid-infrared QCL with a 5.26 μm wavelength was used to detect fundamental vibrational transitions of NO. An effective optical path length of 2.1 km was achieved in a 50 cm long cell using high-reflectivity mirrors. In combination with a particle filter and a membrane gas dryer, stable and sensitive measurement of NO in exhaust gas was achieved for more than 30 minutes with a time resolution of 1 s. The results of this work indicate that a laser based NO sensor can be used to measure NO in exhaust gas over a dynamic range of three orders of magnitude.     

Spectroscopic trace-gas sensor with rapidly scanned wavelengths of a pulsed quantum cascade laser for in situ NO monitoring of industrial exhaust systems

Development of a pulsed quantum cascade laser (QCL)-based spectroscopic trace-gas sensor for sub-part-per-million detection of nitric oxide (NO) and capable of monitoring other molecular species such as CO₂, H₂O, and NH₃ in industrial combustion exhaust systems is reported. Rapid frequency modulation is applied to the QCL to minimize the influence of fluctuating non-selective absorption. A novel method utilizes only a few laser pulses within a single wavelength scan to probe an absorption spectrum at precisely selected optical frequencies. A high-temperature gas cell was used for laboratory evaluation of the NO sensor performance. A noise-equivalent sensitivity (1) of 100 ppb × m/ at room temperature and 200 ppb × m/ at 630 K was achieved by measuring the NO R(6.5) absorption doublet at 1900.075 cm^–1.     

Sensitive detection of CO2 concentration and temperature for hot gases using quantum-cascade laser absorption spectroscopy near 4.2 μm

Mid-infrared quantum-cascade laser (QCL) absorption spectroscopy of CO₂ near 4.2 μm has been developed for measurement of temperature and concentration in hot gases. With stronger absorption line-strengths than transitions near 1.5, 2.0, and 2.7 μm used previously, the fundamental band (00⁰1–00⁰0) of CO₂ near 4.2 μm provides greatly enhanced sensitivity and accuracy to sense CO₂ in high-temperature gases. Line R(74) and line R(96) are chosen as optimum pair for sensitive temperature measurements due to their high-temperature sensitivity, equal signal-to-noise ratio (SNR), weak interference of H₂O transitions, as well as relatively strong line-strengths in high temperature and weak absorption in room temperature. The high-resolution absorption spectrum of the far wings of the R-branch (R56–R100) in the fundamental vibrational band of CO₂ is measured in a heated cell over the range 2,384–2,396 cm^?1 at different temperatures from 700 to 1,200 K. Taking three factors into consideration, including SNR, concentration detectability, and uncertainty sensitivity, the absorption line R(74) is selected to calculate CO₂ concentration. The tunable QCL absorption sensor is validated in mixtures of CO₂ and N₂ in a static cell for temperature range of 700–1,200 K, achieving an accuracy of ±6 K for temperature and ±5 % for concentration measurements.