FTIR光谱遥测红外药剂的燃烧温度

本文利用遥感FTIR光谱，对红外药剂的燃烧特性进行了研究。在分辨率为4cm^-1时，收集4700－740cm^-1波段的光谱。从HF等燃烧产物发射的分子振转基带精细结构的谱线强度分布，可以对燃烧温度进行遥感测定，并给出了燃烧温度随时间的变化关系，实验结果表明燃烧表面附近温度梯度很大，存在着急剧的变化温度场，同时也说明，在不干扰火焰温度场的情况下，利用遥感FTIR光谱对剧烈的、非稳态快速燃烧的火焰温度进行连续实时的遥感测量，是一种快速、准确、灵敏度高的测温方法，显示了它在燃烧温度测量、产物浓度测试以及燃烧机理研究等方面的应用前景。     

Quantitative visualization of temperature field in non-luminous flame by flame reaction technique

Abstract  

An experimental technique for measuring a temperature field in an axisymmetric non-luminous flame is developed using the flame reaction technique combined with the inverse Abel transformation. Flame visualization is carried out using alkali metal solution of Potassium (K), which is supplied to a premixed methane/air flame in a form of spray mist. The basic principle of this technique is based on the measurement of local emission intensity distribution visualized by the flame reaction, which is a function of temperature according to the Maxwell–Boltzmann statistics of thermodynamics. The relationship between the local intensity and the temperature is obtained from the calibration study, in which the local intensity is evaluated from the line of sight intensity by the inverse Abel transformation, and the temperature is measured by thermocouple. This technique is successfully applied to the measurement of local temperature distribution in steady and flickering premixed methane/air flame. The temperature field in the flickering flame indicates that the local temperature oscillates periodically with the flickering frequency, and the highest temperature is found along the flame front and in the merging region.     

Measurement of impurity and temperature variations in water by interferometry technique

Refractive index is an important optical parameter of liquids, which is temperature, concentration and wavelength-dependent. Therefore, precise measurement of refractive index variation can be used for precise determination of the above parameters. In this paper a laser-based interferometry technique was introduced for accurate measuring of the refractive index variation due to temperature, and concentration changes. Distilled water was used as a test liquid sample, however the technique can be applied for any similar liquids. The concentration variations of distilled water due to three different impurities i.e. ethanol, salt water and tap water were examined. The technique gives measurement for concentration and temperature variations typically at the order ∼10⁻⁴(g/l)⁻¹ and 10⁻⁵ K⁻¹ respectively. The results show the variations of refractive index with respect to temperature or concentration can be measured typically with an accuracy of ∼6%, and 10% respectively. The method is useful for fast and precise monitoring of temperature and concentration variations in transparent liquids.     

量子真空计量标准中的非极性稀薄气体折射率测量研究

为进一步提高真空量值的复现性和准确性,最新研究采用量子技术实现对真空量值的测量与表征.该方法利用Fabry-Perot谐振腔实现腔内气体折射率的精密测量,并反演出气体密度,进而获得对应的真空量值,其中气体折射率的测量是影响真空量值准确性的关键.本文基于第一性原理,利用从头计算理论计算了在已知压力和温度条件下的氦气折射率,给出腔内气体压力与折射率关系的表达式,并利用基于Fabry-Perot激光谐振腔的真空测量装置,通过双腔谐振激光拍频精确测量了充气前后谐振激光频率的变化,测出了氦气折射率,并分析了测量不确定度.将理论计算值与实验测量值进行了对比分析,得出了制约准确度提高的主要因素,并提出了修正方法.     

激光诱导热光栅光谱测温技术研究

报道了激光诱导热光栅光谱测温技术的研究. 通过两束相干交叉的脉冲抽运光, 在NO₂/N₂混合气中诱导出热光栅, 一束满足布拉格散射条件的连续探测光在交叉区域激励出相干的热光栅信号, 经过空间和光谱滤波的信号光由光电倍增管探测, 并由数字示波器显示和存储. 该信号携带了丰富的流场信息, 通过频域分析, 对气体的温度进行了测量, 热光栅光谱技术测量的温度与热电偶温度符合得很好. 同时还利用热光栅光谱技术进行了气体声速的直接测量, 在一定的温度范围内, 测量结果与理论曲线基本一致, 显示了该技术具有较高的测量精度与多参数同时测量的能力. 对影响信号波形的因素进行了分析, 结果表明, 热光栅光谱测温技术在高压强环境下应用具有独特的优势, 是一种应用前景广阔的激光燃烧诊断技术.     

Thermodynamics of a quantized electromagnetic field in absorbing media

Because induced emission is an incoherent phenomenon, it is impossible to represent the Gibbs thermodynamic potential of a quantized electromagnetic field in an absorbing medium in terms of the standard refractive index with an imaginary component. This is completely true with respect to the entropy of the electromagnetic field, the heat capacity, and the state equation, as well as to the stationary ponderomotive forces. The so-called causal refractive index arises in the theory, which differs from the standard refractive index in the analytical properties. The ideality condition of the photon gas in dissipative media does not hold without using the causal refractive index. The Kirchhoff law holds true only if the causal refractive index negligibly differs from unity.     

Optical fiber Bragg grating hydrogen sensor based on evanescent-field interaction with palladium thin-film transducer

Fiber Bragg grating (FBG) sensors in single-mode optical fibers are widely applied for measurement of temperature and strain. If exposing FBG sensors to an external analyte by planar side-polishing technique of the fiber, evanescent-field interaction yields a Bragg wavelength shift also by changing the refractive index of the analyte. Deposition of sensor-specific transducer layers on the side-polished fiber can specify this spectrally encoding and network-capable optochemical fiber Bragg grating refractometry to the monitoring of specific substances, absorbed gases and vapors. In this paper, the sensor principle is demonstrated for the example of a hydrogen gas sensor based on a palladium thin-film transducer. Hydrogen in 0.1–4% volume concentration range can be monitored by the spectral shift of the Bragg wavelength, which is caused by the decreasing complex refractive index of Pd with increasing absorption of hydrogen.     

Measurement of Dynamic Flow Field by Optical Computed Tomography with Shearing Interferometers

A system of interferometric computed tomography (CT) for measuring temporal variation of refractive index distribution in a transparent medium such as a flow field has been developed. The system adopts shearing interferometers with double-period diffraction gratings to obtain path-length differences between sheared rays. In order to obtain projection images simultaneously six shearing interferometers are placed in six different directions. The image data for the six interferometers are stored in image memories at the rate of 30 frames per second. Refractive index distribution in the sectional plane of the flow field is calculated with the data using the algorithm of CT modified for shearing interferometers. In experiments temporal variations of refractive index distributions due to a flame and gas flow from a nozzle are measured. These experiments verified that the shearing interferometers are suitable for interferometric computed tomography because they are simple in arrangement and insensitive to disturbances such as mechanical vibration. Potential of the shearing technique and comparison between the CT with the shearing type of interferometer and that with another type of wavefront sensor are discussed.     

相敏式激光啁啾色散光谱技术在高吸收度情况下的应用

研究了相敏式激光啁啾色散光谱法在高吸收度情况下的应用.用窄频半导体激光器作为光源,利用一工作于载波抑制模式的铌酸锂电光强度调制器调制单频激光,在单频激光两侧产生两个边频分量,并通过两边频分量产生外差干涉信号.利用外差干涉的相位波动来测量甲烷气体位于1653.7 nm附近的折射率波动,通过气体折射率与吸收系数之间的Kramers-Kronig关系计算甲烷气体浓度.传统的波长调制光谱法受限于郎伯-比尔定律,在应用于高吸收度的情况时,存在灵敏度下降的问题,甚至出现随气体浓度上升输出信号反而下降的现象.实验结果显示,相同实验条件下,波长调制光谱法的线性测量范围为38.1—1500 ppm·m,线性测量的动态范围仅为16 d B;而相敏式激光啁啾色散光谱法在很大的吸收度范围内均具有线性输出,检出限低至47.3 ppm·m,线性测量范围上限为174825 ppm·m,具有超过35 d B的动态范围.     

全场彩虹技术测量喷雾浓度及粒径分布

喷雾颗粒的浓度、粒径等多参数的同时测量是研究喷雾的关键. 对应用全场彩虹技术测量双组分液滴的浓度及粒径分布进行了研究. 基于改进的Nussenzweig理论,对液滴折射率和粒径分布采用无分布函数算法进行最优化求解, 然后通过折射率与浓度的关系反推液滴浓度.用模拟全场彩虹信号对该算法进行了验证, 该算法可准确反演具有单峰分布、双峰分布粒径特征的液滴群的折射率与粒径分布. 并对体积分数从0%到100%的乙醇溶液喷雾进行了实验测量, 结果表明,所测得折射率与理论值符合,粒径分布稳定.该技术在喷雾浓度测量方面具有广阔的应用前景. 关键词： 全场彩虹技术 折射率 粒径 组分     

Silicon-carbide-based extreme environment temperature sensor using wavelength-tuned signal processing

A wavelength-tuned signal-processing approach is proposed for enabling direct unambiguous temperature measurement in a free-space targeted single-crystal silicon carbide (SiC) temperature sensor. The approach simultaneously exploits the 6H SiC fundamental Sellmeier equation-based wavelength-sensitive refractive index change in combination with the classic temperature-dependent refractive index change and the material thermal-expansion path-length change to encode SiC chip temperature with wavelength. Presently, the technique is useful for fast coarse temperature measurement as demonstrated from room temperature to 1000 degrees C using a 10-peak count wavelength-tuned measurement with a 0.31 nm total wavelength change. This coarse technique can be combined with the previously presented two-wavelength signal-processing temperature measurement approach to simultaneously deliver a wide temperature range and a high-resolution temperature sensor. Applications for the sensor range from power plants to materials processing facilities.     

基于吸收光谱和激光干涉技术的气体压力测量方法研究

气体压力光学非接触测量是目前激光技术重要应用领域之一,其中气压测量过程中温度耦合问题是现在面临的研究难点。故而提出一种光谱测量技术与激光干涉技术组合测量方法,通过积分吸光度和折射率融合的方式实现气体压力、温度解耦的目的。分析可调谐半导体激光光谱技术(TDLAS)的直接吸收法测量原理和基于折射率的激光干涉测量原理,建立基于吸收光谱的气压测量模型和基于折射率的激光干涉气压测量模型,通过利用三次多项式拟合吸收谱线强度函数的方式,建立了基于积分吸光度和折射率的气体压力、温度解耦的数学模型。实验搭建了基于TDLAS技术和激光干涉技术的气体压力检测系统,采用中心波长为2 004 nm的可调谐半导体激光器和波长为632.8 nm的激光干涉仪,气室长度为24.8 cm,将CO₂作为研究对象,并以高精度压力控制器和温度传感器的测量结果分别作为压力温度参考值,以真空为背景信号,在室温环境中测量并计算出气体压力变化后积分吸光度值和折射率值,进而解算得到气体压力和温度值。实验结果显示：压力测量结果最大相对误差为3.61%,最小相对误差为0.5%,测量平均相对误差为1.99%;在以开尔文温度为前提下,温度解算结果最大绝对误差为7.66 K,最小绝对误差为0.78 K,测量平均绝对误差为3.29 K,测量结果与参考结果具有较高的吻合度,该研究可为以后光学法测量气体压力温度影响分析提供参考。     

基于无芯光纤的多参数测量传感器

设计并制作了一种基于单模-无芯-单模-无芯-单模光纤结构的马赫-曾德尔传感器,可用来同时测量折射率和温度.该传感器中,两处无芯光纤充当输入、输出耦合器,中间单模光纤作为传感臂.利用有限元仿真和理论分析,确定耦合器和传感臂的最优长度为15 mm.在无芯光纤中激发出的高阶模进入单模光纤的包层传输,由于倏逝场的作用,受到环境折射率和温度的影响.选取透射谱不同干涉级次的波谷作为研究对象,实现了折射率和温度的同步测量.实验结果表明:1545 nm附近干涉谷的折射率和温度灵敏度分别为–153.89 nm/RIU(refractive index unit)和0.166 nm/℃;1570 nm附近干涉谷的折射率和温度灵敏度分别为–202.74 nm/RIU和0.183 nm/℃.该传感器在实现折射率和温度同步测量的同时,仍能保持较高灵敏度,在生物医疗等方面有着较好的应用前景.     

Measuring optical properties of an eye lens using magnetic resonance imaging

We compare the focal lengths of porcine lenses measured optically and by using a novel MRI technique. The geometric properties of the lenses were also measured and compared. The MRI technique exploits the dependence of both the lens refractive index and relaxation rates on the local protein concentration. By measuring the refractive index and corresponding values of R2 (=1/T2) for samples of lens homogenates with different protein concentrations, the dependence of refractive index on R2 was determined empirically. R2 maps, constructed from monoexponential fits to multiecho images of a slice through the lens containing the optical axis, were converted to refractive index maps using this relationship. A simulated ray trace through the refractive index map provided an estimate of lens focal length that was compared to a direct optical measurement of focal length using a laser ray-tracing method. It was found that the mean focal lengths estimated from the two techniques agreed within experimental uncertainty. The refractive index profile along the optical axis was found to be well described by a simple function of the form n=n0 + n1 x ra where r is the (normalized) lens radius.     

Flow field's temperature partition reconstruction based on its phase distribution

Aiming at the effect of species composition distribution on flow field's temperature reconstruction from the experimentally measured refractive index, a temperature partition reconstruction method based on flow field's phase distribution is proposed. Moiré deflection tomography is chosen to obtain the refractive index of a flame with probe wavelength of 808 nm. Enlightened by the visual characteristic of optical computerized tomography (OCT) for flow field and the practical structure of the flame, it is divided into three regions in radial direction based on its phase distribution. The essence is that the temperature is reconstructed with adopting different species composition for different regions. Finally, the rationality of the method is analyzed.     

Diode laser atomic fluorescence temperature measurements in low-pressure flames

Temperature measurements have been performed in a low-pressure flame by the technique of diode laser induced atomic fluorescence. The experiments were done in a near-stoichiometric flat-flame of premixed methane, oxygen and nitrogen, at a pressure of 5.3 kPa. Indium atoms were seeded to the flame and probed using blue diode lasers; the lineshapes of the resulting fluorescence spectra were used to determine the flame temperature at a range of heights above the burner plate. The particular issues associated with the implementation of this measurement approach at low pressure are discussed, and it is shown to work especially well under these conditions. The atomic fluorescence lineshape thermometry technique is quicker to perform and requires less elaborate equipment than other methods that have previously been implemented in low-pressure flames, including OH-LIF and NO-LIF. There was sufficient indium present to perform measurements at all locations in the flame, including in the pre-heat zone close to the burner plate. Two sets of temperature measurements have been independently performed by using two different diode lasers to probe two separate transitions in atomic indium. The good agreement between the two sets of data provides a validation of the technique. By comparing thermocouple profiles recorded with and without seeding of the flame, we demonstrate that any influence of seeding on the flame temperature is negligible. The overall uncertainty of the measurements reported here is estimated to be ±2.5% in the burnt gas region.     

Measurement of radiative gas and particle emissions in biomass flames

Radiation is the dominant mode of heat transfer near the burner of coal and biomass-fired boilers. Predicting and measuring heat transfer is critical to the design and operation of new boiler concepts. The individual contributions of gas and particle phases are dependent on gas and particle concentration, particle size, and gas and particle temperature which vary with location relative to the flame. A method for measuring the contributions of both gas and particle radiation capable of being applied in harsh high temperature and pressure environments has been demonstrated using emission from particles and water vapor using an optical fiber probe transmitting a signal to a Fourier Transform Infrared (FTIR) spectrometer. The method was demonstrated in four environments of varying gas and particle loading using natural gas and pulverized wood flames in a down-fired 130?kW_th cylindrical reactor. The method generates a gas and particle temperature, gas concentrations (H₂O and CO₂), total gas and particle intensities, and gas and particle total effective emissivity from line-of-sight emission measurements. For the conditions measured, downstream of the luminous flame zone, water vapor and CO₂ radiation were the dominant modes of heat transfer (effective emissivity 0.13–0.19) with particles making a minor contribution (effective emissivity 0.01–0.02). Within a lean natural gas flame, soot emission was low (effective emissivity 0.02) compared to gas (0.14) but within a luminous flame of burning wood particles (500?µm mean diameter) the particles (soot and burning wood) produced a higher effective emissivity (0.17) than the gas (0.12). The measurement technique was therefore found to be effective for several types of combustion environments.     

High-precision measurement system based on laser interferometer for determining alcohol concentration of liquid solution

This study develops a high-precision, non-destructive measurement technique based on a laser interferometer for determining the alcohol concentration of a liquid solution from its refractive index. The optical metrology system is employed to measure the refractive indexes of samples with known alcohol concentrations ranging from 5% to 95%. By applying regressional analysis to the experimental results, an analytical expression is derived to describe the quadratic relationship between the refractive index and the alcohol concentration. An excellent agreement is observed between the experimentally determined values of the alcohol concentration and the analytically predicted results. For an assumed laser interferometer resolution of 1 nm, the measurement resolution of the proposed metrology system is found to be at least F = 0.0025%, which is significantly better than that of typical stereometry methods (approximately 1.0%) Furthermore, it is shown that the measurement resolution improves as the alcohol concentration reduces.     

色散、群速与群折射率

本文讨论了群折射率存在的物理意义,指出群折射率不仅包含了折射率概念而且还体现了折射率的色散性质,同样能作为材料本身的光学性质参量.接着指出在折射率的白光干涉法测量中存在着忽视色散作用而导致的将群折射率误认为折射率的情况.将群折射率与折射率区别开来,不仅可以消除折射率测量中所存在的错误,而且可以突出色散现象在光传播时间特性上的意义.为此建立了折射率与群折射率的相互变换关系,通过对于典型物质的折射率与群折射率变换关系的计算,说明二者在数值上的差别甚至对于气体介质来说也是不能忽略的.     

Feasibility of optical computerized tomography for measuring the species concentration distribution of flow fields

In this paper, the feasibility of using optical computerized tomography (OCT) methods for measuring the distribution of species concentration for flow fields is analyzed and discussed. First, feasible methods are chosen for two or three objects composed flow fields from the perspective of the measurable principle. Second, both common gas and plasma are chosen as two typical examples for specific analysis and discussion. The results show that the feasibility and applicable range of OCT methods are related to the temperature, pressure, and species composition of the measured flow fields. Finally, the study indicates that OCT methods are more suitable for measuring the distribution of species composition for common gas rather than plasma. In a word, this study could be helpful for extending the applicable range of OCT methods, which are based on the measurement of the refractive index.