多组分传质过程的Maxwell-Stefan方法模拟

为定量研究多组分系统在多孔介质内传质过程中组分之间的交互作用现象,本文基于Maxwell-Stefan模型对CH₄/Ar/H₂混合气体在单个直孔道内的纯扩散过程和C₂H₆/C₃H₈/N₂混合气体在活性炭上的吸附扩散过程进行了模拟,定量地描述和分析了多组分系统中组分之间在传质过程中的交互作用。研究表明:对于扩散过程,组分之间的交互作用表现为大分子对小分子的拖带;对于吸附过程,这种作用表现为强吸附质能够替代已被吸附在吸附剂表面的弱吸附质;主体扩散为主要的传质形式。     

The retrieval of profile and chemical information from ground-based UV-visible spectroscopic measurements

An algorithm has been developed to retrieve altitude information at different diurnal stages for trace gas species by combining direct-sun and zenith-sky UV-visible differential slant column density (DSCD) measurements. DSCDs are derived here using differential optical absorption spectroscopy. Combining the complementary zenith-sky measurements (sensitive to the stratosphere) with direct-sun measurements (sensitive to the troposphere) allows this vertical distinction. Trace gas species such as BrO and NO₂ have vertical profiles with strong diurnal dependence. Information about the diurnal variation is simultaneously retrieved with the altitude distribution of the trace gas. The retrieval is a formal optimal estimation profile retrieval, allowing a complete assessment of information content and errors.     

Random-hole optical fiber evanescent-wave gas sensing

Research on development of optical gas sensors based on evanescent-wave absorption in random-hole optical fibers is described. A process to produce random-hole optical fibers was recently developed that uses a novel in situ bubble formation technique. Gas molecules that exhibit characteristic vibrational absorption lines in the near-IR region that correspond to the transmission window for silica optical fiber have been detected through the evanescent field of the guided mode in the pore region. The presence of the gas molecules in the holes of the fiber appears as a loss at wavelengths that are characteristic of the particular gas species present in the holes. An experimental setup was constructed with these holey fibers for detection of acetylene gas. The results clearly demonstrate the characteristic absorptions in the optical spectra that correspond to the narrow-line absorptions of the acetylene gas, and this represents what is to our knowledge the first report of random-hole fiber gas sensing in the literature.     

Thermal effects of a laser beam tube consisting of a window and nonflowing gas

High-energy laser systems include an optical train and a gas medium that must be capable of transporting and directing the beam. The optical train is termed a laser beam tube. Because of the finite absorption of laser energy, the thermal effects of the beam tube make the beam diffuse and cause degradation of the laser beam's quality. We study systematically a beam tube consisting of a laser window made from white bijou (i.e., Al2O3) or fused silica and a tube of nonflowing nitrogen or helium gas. The results show that the thermal effects of the window and the gas on the beam neutralize each other; in particular, in some cases they compensate for each other completely, such that the beam tube has no effect on the beam quality in spite of the fact that separately each has a severe effect. We explain how to acquire the specific cases.     

Broadly tunable mid-infrared VECSEL for multiple components hydrocarbon gas sensing

A new sensing platform to simultaneously identify and quantify volatile C1 to C4 alkanes in multi-component gas mixtures is presented. This setup is based on an optically pumped, broadly tunable mid-infrared vertical-external-cavity surface-emitting laser (VECSEL) developed for gas detection. The lead-chalcogenide VECSEL is the key component of the presented optical sensor. The potential of the proposed sensing setup is illustrated by experimental absorption spectra obtained from various mixtures of volatile hydrocarbons and water vapor. The sensor has a sub-ppm limit of detection for each targeted alkane in a hydrocarbon gas mixture even in the presence of a high water vapor content.     

差分吸收光谱反演方法在环境监测系统中的研究

差分吸收光谱(DOAS)技术在大气/烟气污染物排放环境监测中有广泛的应用。文章首先对这种方法进行了介绍和分析,通过公式推导出被测量气体的差分吸收光谱和参考差分吸收截面光谱所包含的面积具有线性关系,并由此给出了一种新的气体浓度计算方法,即直接用差分吸收面积拟合法代替最小二乘方法,从而避免了光谱不同分辨率、光谱漂移、拉伸或压缩等因素对测量结果造成的误差,同时这种方法具有计算量小和处理速度快等特点。最后,在自行研制的烟气DOAS测量系统上测量了四种浓度的SO₂标准气体,实验结果验证了该方法在实验室条件下的有效性。     

Impedance characteristics of three-phase electrodes on solid electrolytes

Previously obtained theoretical expressions for the impedance associated with the diffusion of neutral species through a permeable electrode and along the electrode/electrolyte interface are discussed as they apply to gas electrodes on solid electrolytes. A new result, describing diffusion under circular electrode contacts, is obtained. Representative impedance-plane, admittance-plane and Bode-type plots are given for each theoretical model. The effects of rate-controlling adsorption-desorption exchange with the gas phase are considered, as is the applicability of the idealized theoretical models to irregular electrodes.     

Population inversion induced by collisions in a two level system under nonresonance optical excitation

When the gas particles, which can be considered as a two level quantum system, are affected by frequent collisions with buffer gas particles (thermal reservoir), the spectral densities of the Einstein coefficients for absorption and induced emission are unequal to each other far from the absorption (emission) line. The relationship between the spectral densities at the specified condition reveals new physical phenomena. The mostly convincing example is the fact that population inversion is established in a two level system under nonresonance optical excitation. This effect is experimentally observed as a lasing on sodium resonance transitions.     

有机光伏电池物理性能的模拟

在分析有机聚合物光伏器件物理工作过程的基础上,依据光学原理和扩散理论建立了非相干光吸收模型和激子传输模型. 模拟了限制光伏效率的光学吸收和激子扩散两个主要过程,获得了薄膜厚度与光学吸收、转换效率之间的函数关系,为增强有机薄膜的光学吸收、激子分离与传输并获得高转换效率的有机光伏电池奠定理论基础. 关键词： 有机光伏电池 光学吸收 激子扩散 模拟     

用Bragg光纤测量气体浓度

基于气体的光谱吸收特性,本文提出了一种采用Bragg空芯光纤作为吸收池的新型光纤气体传感器.运用解析法和微扰分析法求解了Bragg空芯光纤中的相对灵敏系数.由于场分布主要集中在芯区,对气体损耗较为敏感,因此,这种光纤气体传感器具有灵敏度高、快速响应、结构简单的特点.耦合多个波长可实现对多种气体同时测量.     

Determination of the diffusion coefficients of dyes in polymer media by the absorption method with a high spatial resolution

The coefficients of diffusion of coumarin 7 in polyurethaneacrylate are determined by a new optical absorption method based on measurement of the absorption gradient at the boundary between the colored and colorless sections of the polymer. The dependence of the diffusion coefficient on concentration is found. The obtained values for the diffusion coefficients of the dye in an elastic matrix allow one to consider that the gradient optical elements in elastomers will be characterized by a relatively large lifetime. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 457–460, July–August, 2000.     

被动多轴差分吸收光谱技术监测大气NO_2垂直廓线研究

痕量气体垂直廓线的监测,对大气污染研究具有重要意义。介绍了被动多轴差分吸收光谱(MAX-DOAS)技术监测痕量气体垂直廓线的光学遥感方法。研究中MAX-DOAS测量多个角度的斜柱浓度、结合大气辐射传输模型,利用最优估算法反演出痕量气体垂直廓线,并对最优估算法参数选取和反演评估进行了详细描述。将该技术应用于合肥地区NO2垂直廓线的监测:通过与长光程差分吸收光谱仪的测量结果对比,相关系数达到0.80。该技术为大气环境立体监测提供了一种简便的方法。     

基于Ring-down光学谐振腔的新型瓦斯传感器

提出将光谱吸收型传感技术和Ring-down光学谐振腔理论相结合的设计思路,将吸收光强与气体含量之间的定量关系与Ring-down光学谐振腔理论有机结合起来,设计了基于Ring-down光学谐振腔理论的光学瓦斯(甲烷)气体传感器气体吸收腔,以解决传统瓦斯传感器因为气体的谱宽很窄而难以提高微弱信号检测精度和灵敏度的问题....     

InSb纳米晶体的生长和吸收光谱的研究

采用在惰性气体中蒸发的方法获得了沉积在ZnS基片上的InSb纳米晶体,其平均尺寸随惰性气体的压强增加而增大.从实验测量的室温吸收谱上看到,当纳米晶体的平均直径从27.9 nm减小到24.2nm再到21.4 nm时,其吸收边分别向高能方向移动了0.0151 eV和0.0145 eV.用有效质量近似模型计算了半导体纳米晶体的吸收边相对其体材料的移动,将理论计算与实验结果进行了比较.     

超光谱成像差分吸收光谱技术研究

基于散射光的被动差分吸收(DOAS)技术利用气体的特性吸收谱线可实现对不同大气污染气体的定量测量,介绍了一种基于成像光谱仪的光学遥感系统,该系统运用被动DOAS原理实现了对大气污染气体的二维成像测量,并报道了该系统对实验室样品池一维测量与城市道路上方NO₂组分的成像测量实验. 基于成像光谱仪的被动DOAS系统利用太阳散射光可获取垂直方向一维的光谱信息,结合扫描装置,便可实现对污染气体的二维成像解析. 关键词： 被动差分吸收光谱 成像光谱仪 污染气体 二维成像     

高浓度气体共振光声光谱信号饱和特性研究

采用恒流驱动耦合机械斩波技术在激光光声光谱装置上系统测量了5%—100%宽浓度范围甲烷气体的共振光声信号,发现在高浓度区共振光声信号呈现异常的饱和特征.基于气体吸收和光声光谱原理定量分析了光声信号饱和的主要原因及影响因素,研究表明,气体样本对入射光强吸收而导致的声源与本征共振模式的耦合系数改变是异常饱和的主要原因,并导出判定光声信号饱和深度的准则以用于判定高浓度气体饱和深度。     

Theory of optical ramsey resonance in three separated fields produced by a corner reflector

In this paper we study the optical Ramsey resonance signal of two-level molecules in three separated fields consisting of one standing wave and two traveling waves of opposite directions with each other. Their separations and phase differences are given by a corner reflector. The transition probability of a molecule that traverses the three interaction regions is calculated by using an optical Bloch vector formalism. It is then integrated over distributions of molecular velocities and positions to evaluate the signal observed with a gas cell. The result is applied to compute the optical Ramsey resonance signal in the absorption line of CH₄ at 3.39 μm. Variations of the Ramsey resonance lineshape and the intensity with the gas pressure and the field intensity are obtained.     

飞秒光学频率梳高精度气体吸收光谱技术进展

飞秒光学频率梳以其频谱宽、脉宽窄、频率稳定度高等优点,对光学频率计量、绝对距离测量、高精度光谱测定产生重大影响。飞秒光学频率梳的时域特性和频域特性溯源至微波频率基准,使得高精度气体吸收光谱探测成为可能。飞秒光学频率梳光谱技术具有测量速度快、光谱灵敏度高、分辨率高、信噪比高等优点,因此加大对飞秒光学频率梳光谱技术的研究力度将更好地服务于环境保护、工业生产、生物医学、科学研究等各领域。飞秒光频梳高精度气体吸收光谱主要可分为光频梳腔衰荡光谱、光频梳腔增强光谱和双光频梳多外差光谱。其中,根据采集方式不同,光频梳腔增强光谱又可分为梳齿游标测量法、虚拟成像相位阵列测量法和傅里叶变换测量法。目前,国外已广泛开展相关研究,而国内仍处于起步阶段。本文综述了飞秒光学频率梳高精度气体吸收光谱探测的主要技术方法,展示了不同测量方法典型的实验方案,分析了各探测方法的优缺点,并追踪了主要研究小组的前沿成果。     

On the investigation of the diffusion processes of photoexcited carriers in silicon by ps-reflectivity measurements

The optical excitation of non-equilibrium charge carriers in semiconductors results in a carrier distribution which gives rise to a diffusion process into the bulk of the semiconductor. The diffusion time depends on the absorption coefficient and on the ambipolar diffusion constant. These diffusion times are on a subnanosecond time scale for our experimental conditions. By time-resolved reflectivity measurements we have studied the dependence of the ambipolar diffusion constant on the density of excited carriers. Experimental results were compared with theoretical ones.     

基于可调谐二极管激光吸收光谱的气池光程可溯源测量

在碳中和的国际大背景下,精确可靠地定量测量大气温室气体浓度对实现碳中和目标具有重要意义,开发测量结果可直接溯源至国际单位制SI的气体分析仪是精确可靠监测温室气体浓度的重要方法。可调谐二极管激光吸收光谱（TDLAS）技术是常用的气体浓度测量方法,根据比尔-朗伯定律,实现仪器的测量浓度直接溯源至SI的必要条件之一是可直接溯源的气池光程,气池光程的不确定度直接影响气体浓度的测量不确定度,对气池光程的可溯源精确测量有利于发展测量结果可直接溯源的气体分析仪。针对光程标称为81 cm的三次反射型气池光程可溯源测量需求,使用校准的米尺测量该气池光程得到的直接测量结果为(81.21±0.80) cm,较大的测量不确定度（0.80 cm）是综合考虑定位误差和三段光路与测量路径可能不重合导致的测量误差估算得到的。为了减小测量不确定度,本文搭建了TDLAS气池光程测量系统,测量系统以1 576 nm分布式反馈激光器为光源,通过在激光控制器上加载斜坡扫描电压来测量待测气池内标准高纯二氧化碳（CO₂,99.999%）在6 344.68 cm-1附近的吸收光谱,使用测量结果可直接溯源的压力传感器和温度传感器分别测量气池内的压强和气体温度,采用美国国家标准技术局最新测量得到的30012-00001跃迁带P 4e支线强（相对标准不确定度为0.15%）反演气池光程,使用二次速度依赖Voigt线型精确拟合不同气压（36~75 Torr）下的光谱吸光度信号获得对应气压的积分吸光度,全面分析各参量的测量不确定度及其传递过程,对不同气压下的积分吸光度进行线性回归分析,计算得到可直接溯源的气池光程为(81.61±0.42) cm,相对标准不确定度为0.51%,测量不确定度范围落在直接测量结果范围内,测量不确定度小于直接测量结果。本文气池的光路结构是多次反射长光程气池的简化,该系统同样适用于多次反射长光程气池光程的可溯源测量。