利用可调谐激光吸收光谱技术对光路上气体温度分布的测量

利用可调谐激光吸收光谱技术(TDLAS),扫描多条吸收谱线以实现气体温度分布的测量。文章给出了温度分布测量的原理和方程离散化的方法,在气体浓度和压力均匀时,利用带约束最小二乘法计算得到温度分布。根据HITRAN中6 330 cm-1附近的4条CO谱线的参数,建立了温度在300和600 K时,路径长度均为55 cm的两段温度分布模型,模拟了测量误差与温度区间长度约束条件的影响。结果表明随着测量误差的增大和约束条件的减弱,计算结果误差相应增大。在5％的测量误差下,计算结果的最大误差为11％,平均误差为2.2％。以管式炉中的高温段和室温下的低温段作为两段温度分布模型进行试验。利用6 330 cm-1处的垂直腔面发射激光二极管(VCSEL)扫描得到的4条CO谱线,通过背景信号的三次多项式拟合得到基线,求出温度分布计算所需的光谱吸收率积分值。在四种情况下, 计算温度分布结果与模型误差分别为7.3％,6.5％,4.7％和2.7％。     

TDLAS气体浓度反演的状态空间方法

 针对基于可调谐激光二极管吸收光谱技术（TDLAS）的气体浓度测量系统,建立了气体状态空间模型,并将卡尔曼滤波算法应用于TDLAS浓度反演中。实验表明卡尔曼滤波可以很好地消除测量噪声和模型误差对实验结果的影响,与最小二乘拟合的方法相比,在相同信噪比下反演精度可以提高1倍以上。     

可调谐半导体激光吸收光谱技术应用于平面火焰中气体浓度二维分布重建的研究

研究了可调谐半导体激光吸收光谱技术实现气体浓度二维分布测量的方法,探索了重建气体浓度二维分布的模型和算法,并采用数值模拟的方式对重建程序进行了可行性验证。搭建了由24束激光束构成的场参数测量系统,以甲烷/空气预混火焰中H₂O为测量对象,运用重建程序重建了火焰中H₂O浓度的二维分布,实验结果分析表明,重建结果较真实的反应了火焰中H₂O浓度的二维分布状态,为实现优化燃烧控制提供重要数据。     

Trace gas detect based on spectral analysis and harmonic ratio

Optical Review - A novel method of gas concentration calibration for tunable diode laser absorption spectroscopy, in which spectral analysis and harmonic signal intensity ratio measurement are...     

基于调谐二极管激光吸收光谱的燃气管道泄漏探测研究

根据可调谐二极管激光吸收光谱及谐波探测的原理,建立以分布反馈式半导体激光器为可调谐光源,利用多次反射池进行点式采样的实验装置。基于甲烷分子1 653.7 nm附近的吸收线,实验研究二次谐波信号对甲烷浓度的响应线性,并实现空气中甲烷本底含量的测量。研究结果表明可调谐二极管激光气体检测技术可为城市燃气管道泄漏探测提供了一种灵敏度高、抗干扰能力强的有效手段。     

Optical–feedback cavity–enhanced absorption: a compact spectrometer for real–time measurement of atmospheric methane

We report on the application of the new technique of optical–feedback cavity–enhanced absorption spectroscopy to the real–time quantitative measurement of tropospheric methane traces from an airplane using a compact, low cost instrument based on a telecommunication–type diode laser operating close to room temperature. Methane concentration is obtained by fitting the absorption line centered at 1658.96 nm (6026.23 cm^-1) which belongs to the first overtone transition of the CH stretch vibration. The measurement rate is about 30 Hz, but the response time is limited to about 0.3 s by the gas flow in the measurement cell. The instrument provides the absolute ambient methane concentration accurate to ±1% (±20 ppb) without need for a periodic calibration. This is demonstrated by a hands–off comparison with a self–calibrating chromatographic setup during 10 days. The observed measurement stability can be extrapolated to much longer time periods. With respect to the short–term performance (minutes) fast concentration changes at the level of 1 ppb can be detected, and we believe this performance can be extended to the long term. Finally, a laboratory comparison with a lead–salt mid–infrared diode laser multipass spectrometer (operating close to 3028 cm^-1 at liquid nitrogen temperature) demonstrates a similar performance. PACS 07.88.+y; 42.55.Px; 42.62.Fi     

1.3μm注入锁定半导体激光器及其远场特性

报道了利用１．３μｍ分布反馈（ＤＦＢ）半导体激光器注入锁定普通半导体激光器后的模式及其远场分布特性实验。在不加隔离器和主被协激光器偏振方向相互垂直的情况下，获得了静态和动态单纵模运转，并观察和测量了普通半导体激光器注入锁定前后输出光的远场分布，最后对实验结果进行了讨论。     

基于多波长激光吸收光谱技术的气体浓度与温度二维分布遗传模拟退火重建研究

利用可调谐半导体激光吸收光谱技术实现气体浓度温度二维分布重建.设计了气体浓度温度二维分布重建测量系统,采用四路波分复用技术以减少投影光路布置数量和增加气体吸收测量信息.针对于图像重建过程中建立的非线性投影方程组,将遗传算法与模拟退火算法相结合进行求解,在实现全局最优搜索基础上提高算法搜索效率.建立燃烧环境下H2O浓度温度二维分布模型,借助于近红外波段1.3—1.5μm范围内4条H2O气体吸收谱线,利用数值模拟计算方法进行了气体分布重建,重建结果与模型符合得很好.通过在投影数据中添加不同比例的随机误差,考察其对气体分布重建结果的影响.研究表明,气体浓度分布重建结果对于投影误差不敏感,而增加投影误差幅值将导致温度分布重建均方误差增大。     

基于QCL-TDLAS的NH3浓度测量仿真研究

可调谐半导体激光吸收光谱（tunable diode laser absorption spectroscopy,TDLAS）作为一种新型气体浓度测量技术被广泛应用于NH₃浓度测量领域。利用Matlab可视化建模仿真软件Simulink分别实现了以中远红外量子级联激光器（quantum cascade laser,QCL）和近红外分布反馈式激光器（distributed feedback laser,DFB）做为光源的NH₃浓度TDLAS直接吸收测量仿真,并且分别在常温常压和烟气脱硝出口环境参数下理论分析了NH₃浓度测量灵敏度、检测限和分辨率。仿真结果表明:与传统近红外DFB光源相比,QCL-TDLAS系统理论灵敏度高约50倍,检测限与分辨率可达ppb量级,痕量NH₃浓度测量能力得到大幅度提升。仿真过程和结果为QCL-TDLAS技术在NH₃浓度测量方面的研究提供了理论依据。     

基于可调谐激光吸收光谱技术的多条吸收谱线重建气体浓度二维分布的研究

针对二维气体浓度分布,主要选用多条H₂O的吸收谱线,采用代数迭代重建算法,研究了在激光光束较少且假定温度分布已知的情况下,即不考虑燃烧场中温度对谱线强度的影响时,不同谱线条数对二维浓度重建结果的影响,对比了在同一浓度模型下通过增加激光光束与增加H₂O吸收谱线条数对气体浓度重建结果的影响;研究了增加谱线条数重建气体浓度分布对不同温度与浓度分布模型的适应情况,其中,文中所选取的多条吸收谱线可以由一个激光器同时扫描得到。浓度测量区域采用10×10的网格划分,测量区域中的温度和浓度分布采用单峰不均匀分布与双峰不均匀分布,重建过程中计算了吸收谱线与激光光束的有效利用率。重建结果表明在激光光束较少时,增加吸收谱线条数可以获得更多与浓度相关的谱线参数信息,且与增加激光光束相比可以明显改善浓度重建结果,更主要的是增加谱线条数可以有效降低实验中硬件设备的成本投入以及测量系统的复杂性。     

Direct near-field phase measurement of laser diodes employing a single-mode fiber interferometer

A method of direct measurement of near-field phase and intensity distribution of laser diodes employing a single-mode fiber interferometer is proposed and demonstrated. The phase and intensity of the output beam of the laser in the vicinity of the output facet are measured directly via interferometry. Using a 980 nm laser diode as an example, we obtained a beam width of 0.9 and 3.6 μm at the output facet in the vertical and horizontal axes, respectively. In addition, the phase information of the output beam was also obtained by using interferometry. This technique is particularly useful for laser diodes whose near-field phases are difficult to measure directly. The measured vertical and horizontal wavefront radius of curvatures of a laser diode are in good agreement with the calculation from Gaussian beam theory. Detailed understanding and measurement of the near-field phase and intensity distributions of light sources and optical components are essential for micro-optic designs with better mode matching to minimize the insertion loss.     

可调谐激光吸收光谱法与气相色谱法监测甲烷的对比研究

甲烷是一种重要的温室气体,它对大气中温室效应的贡献仅次于二氧化碳.针对环境空气中甲烷的测定,从测量原理、测量过程和测量装置等方面比较了可调谐二极管激光吸收光谱和气相色谱法两种测量方法.结果表明用上述两种方法测得的甲烷的日变化趋势具有良好的一致性.相比较而言,后者造价更低,并且更方便.     

高双折射光纤中模式耦合空间分布的干涉测量法

本文应用干涉技术测量高双折射偏振保持光纤中模式耦合点的空间分布，测量系统由采用宽带来半导体激光器作为光源的调制迈克尔逊干涉仪组成，通过光程扫描方法探测沿高双折射光纤分布的模式的耦合点。     

利用光频梳提高台阶高度测量准确度的方法

提出一种利用光频梳和可调谐半导体激光器提高台阶高度测量准确度的方法. 通过将可调谐激光器锁定至光频梳,可对激光器的输出波长进行精确锁定与测量.基于可调合成波长链原理,利用锁定后的半导体激光器构建了一套台阶高度测量方案,该方案可消除合成波长误差对台阶高度测量不确定度的影响. 采用一台可调谐半导体激光器和光频梳进行了5000 s的连续锁定实验, 结果表明,锁定后的可调谐半导体激光器的频率稳定度达 1.8×10^-12.该方法的理论测量不确定度约为7.9 nm, 且测量结果可溯源至时间频率基准.     

基于最小二乘法的激光吸收光谱非均匀温度/浓度分布研究

研究了可调谐半导体激光吸收光谱技术实现非均匀温度/浓度分布测量。通过扫描多条H₂O吸收谱线,利用最小二乘算法求解非线性方程,数值模拟和实验得到沿光路方向上的两区温度和浓度分布。计算结果表明采用10条H₂O吸收谱线,计算得到温度相对模型温度的最大偏差为8.3%,浓度偏差为7.6%。通过增加扫描吸收谱线数目和减少未知数个数可以提高计算结果精度。实验测量得到高温区和低温区温度较热电偶读数偏差分别为13.8%和3.5%,数值计算结果与实验结果基本吻合。     

Investigation of the Concentration Dynamics of H2O and HDO Molecules in a Discharge

Physics of Atomic Nuclei - The results of a joint measurement of the concentration of H2O and HDO molecules in a glow discharge in a quartz tube by the modified method of diode laser spectroscopy...     

Simulation and design of applied hollow-duct used for side-pumped cutting-edged of high power disk laser

In this article a ray tracing method is used to design a specific hollow-duct whereby we show that it will be the best choice for pumping the gain medium that has inclined sides or cutting edges used for edge-pumped high power disk laser due to several advantages of the shape of this gain medium. This kind of hollow-duct which is called non-symmetric hollow-duct in this paper includes inclined output facet that compresses and homogenizes the emission of laser diode arrays which are coupled to the entrance-inclined surface of the gain medium. In this paper, the goals of designing this kind of hollow-duct are based on two important criteria: First, homogeneity of pump light distribution due to the beam concentration of laser diode bars according to the edge-pumped disk laser. Second, uniform distribution of pump light in non-symmetric hollow-ducts deducing uniform temperature distribution in the gain medium.     

Wavefront measurements of diode laser beams with large dynamic ranges

We propose and demonstrate a method for the measurement of the wavefronts of high-power diode laser beams with large dynamic ranges. Our wavefront sensor consists of a movable pinhole and a wavefront-slope detector. The measurement results show that the wavefront sensor exhibits a large dynamic range of pi/2 to -pi/2 and a high precision on the measured average wavefront slope. The wavefronts of high-power diode laser beams having large divergence angles at arbitrary locations (including near and far fields) can be reconstructed via the wavefront measurement at a given location. The amplitude and phase distributions of a laser beam could be determined from the measured optical field data using diffraction theory. The experimental measurement of the wavefront of a 980 nm diode laser beam will be presented and discussed.     

基于可调谐半导体激光吸收光谱的氧气测量方法的研究

O₂是工业过程中广泛应用的重要气体, 在工业生产环境下实现O₂浓度的快速在线检测对提高燃烧效率和节能减排具有重要的意义。可调谐半导体激光吸收光谱谐波探测技术是一种具有高灵敏、高选择性、快速响应等特点的气体检测新技术,该技术利用了半导体激光器的可调谐和窄线宽特性,通过精心选择待测气体的某条吸收线可排除其他气体的干扰,实现待测气体浓度的高灵敏快速在线检测。文章以可调谐分布反馈(Distributed feedback, DFB)半导体激光器作为光源,通过波长调制方法对760 nm附近氧气某一吸收线的二次谐波信号测量,从而实现了对氧气浓度的快速在线检测。系统指标达到：检测范围0.01%～20%;检测精度0.1%;长期稳定性1%。     

基于菲涅尔反射的液体浓度精确测量系统

利用菲涅尔反射定律提出了一种测量液体浓度的新方法。整个实验装置结构简单,主要由一个激光光源、三个光耦合器、两个光电探测器组成。光源所发出的光经过三个光耦合器后传输至光纤-液体表面发生反射,反射回的光由两个光电探测器接收。在测量过程中引入参考光路,利用相对技术,使得被测液体的浓度值仅由相对接收光强R决定,从而很好地解决了光源稳定性、环境干扰等测量难题。实验以食盐溶液和蔗糖溶液为测量对象,实验结果与理论分析十分吻合。整个实验装置结构简单,测量精度高,易于操作,测量稳定性能够达到99%以上。