模拟溢油样品激光诱导荧光光谱的偏振特性研究

激光诱导荧光是海洋溢油探测的有效手段之一,但该技术的应用易受自然水体中叶绿素、CDOM等物质荧光信号的干扰。为了寻求排除自然水体荧光干扰的方法,基于532 nm连续激光器搭建了激光诱导偏振荧光实验装置,并针对六种不同密度的模拟溢油样品和自然水体开展了荧光光谱偏振特性研究。实验结果发现,与自然水体的荧光光谱不具有明显的偏振特性不同,所有模拟溢油样品的诱导荧光均具有明显的偏振特性,这一结论说明激光诱导荧光光谱的偏振特性可以作为排除叶绿素、CDOM等物质荧光干扰的依据。实验还发现,溢油样品的荧光偏振性质因样品种类而异。在线偏振光激发下,原油样品荧光偏振度随波长逐渐降低,其中重质原油样品偏振度降低幅度最大,轻质原油样品幅度最小,而柴油样品荧光偏振度没有明显变化;当周期性改变激发光的偏振状态时,所有模拟溢油样品的荧光偏振度随之发生趋势相同的周期性波动,中质样品荧光偏振度波动的幅度低于重质样品,但明显超过轻质样品。这一结果说明,模拟溢油样品诱导荧光偏振度的波长变化特性及对激发光偏振态的响应特性均与样品密度存在一定关联,其偏振特性可以作为辅助油种识别的重要参量。     

Temperature dependence of intensities of laser-induced fluorescences of ethylbenzene and naphthalene seeded in gas flow at atmospheric pressure

The present study has been carried out with the aim of developing a technique for measuring two-dimensional gas temperature profiles based on two-color fluorescence induced by a one-color laser. The laser sheet of the fourth harmonic (266 nm) from a Nd:YAG laser induced fluorescence in species doped in a nitrogen gas flow. The LIF spectra of seven fluorescent species, namely acetone, methylethylketone, acetaldehyde ethylbenzene, anisole, aniline, and naphthalene, were measured to select the best prospective pair of fluorescent species for this technique. Ethylbenzene and naphthalene show relatively high LIF intensities and their LIF spectra overlap less with each other than with other species. Also, ethylbenzene has a high temperature dependence while naphthalene has a low temperature dependence. Thus by selecting one portion of wavelengths in the range where ethylbenzene or naphthalene is dominant, the temperature of the gas can be determined using the ratio of LIF intensities of the mixture at the two wavelengths with good temperature sensitivity. In addition, a general principle is presented for finding out an optimum pair of wavelengths to obtain a good temperature sensitivity in those LIF spectra.     

鲜牛奶变质过程的激光诱导荧光光谱研究

本文用激光诱导荧光（LIF）方法对鲜牛奶和酸牛奶变质过程进行了荧光光谱研究,介绍了所用测试系统的组成及测试方法,给出了变质过程荧光谱,并对测试结果进行了分析,研究表明,变质过程与荧光光谱之间存在密切联系。     

Influence of the mineral component in biotissues affected by calcinosis on their laser-induced fluorescence spectrum

Laser-induced fluorescence (LIF) spectra of human cardiac-valve tissues affected by calcinosis and of macroscopic calcinosis formations produced from resected cardiac valves with such pathology were investigated by comparison with analogous spectra of bone and myocardial tissue of an animal, LIF was excited by an excimer laser with λ=248 nm. In the spectrum of macroscopic calcinosis formations, luminescence bands of the mineral component were separted from the band of protein tissues when these tissues were subjected to heat treatment at 700°C. The investigations have shown that the LIF spectrum of a calcified tissue contains fluorescence bands of tryptophan and fluorescence bands of the mineral component (hydroxylapatite). A change in the spectrum of tissues with pathological processes can be cause not only by a relative change in the concentration of collagen elastin, but also by the additional fluorescenced of the hydroxylapatite mineral that is absent in a healthy cardiac tissue. It was found that the change in the spectrum characterized by the ratio of the LIF intensity at λ=330 nm to the LIF intensity at λ=450 nm is sufficiently large. This makes it possible to use measurements of the relative intensity of fluorescence at these wavelengths to control the degree of calcination of cardiac tissue. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 846–849, November–December, 1999.     

Investigation of toluene LIF at high pressure and high temperature in an optical engine

Toluene laser-induced fluorescence (LIF) emission spectra were acquired in an optical engine with excitation at 248 nm. Toluene was homogeneously seeded in pure nitrogen and air which were used as intake gases. Data were acquired during the compression phase without ignition leading to simultaneous increases in temperature and pressure from 20°C and 1 bar to 500°C and 23.6 bar. Compared to LIF emission spectra at high temperature and atmospheric pressure reported in the literature, the toluene-LIF emission signal shifts to longer wavelengths when temperature and pressure increase simultaneously, whereas the spectrally integrated emission intensity is slightly affected by the pressure level.     

Laser-induced fluorescence thermometry and concentration measurements on NOA–X (0-0) transitions in the exhaust gas of high pressure CH4/air flames

Laser-Induced Fluorescence (LIF) excitation spectra in the NOA–X (0-0) band were used for temperature measurements in the postflame region of high-pressure CH₄/air flames. To improve the quality of the measured spectra and to perform reliable line-shape measurements, the initial mixture was doped with approximately 400 ppm NO. At pressures up to 18 bar, excellent agreement was obtained between NO LIF temperatures and NARS/rotational Raman temperatures. Effective broadening coefficients were also determined in these flames. Problems with quantitative concentration measurements of NO and single-pulse temperature measurements at high pressures are discussed.     

Laser-induced fluorescence determination of flame temperatures in comparison with CARS measurements

Temperature profiles in several premixed low pressure H₂/O₂/N₂ flames and in an atmospheric pressure CH₄/air flame were determined by laser-induced fluorescence (LIF) and by CARS experiments. In the LIF study, temperatures were derived from OH excitation spectra, CARS temperatures were deduced from N₂ Q-branch spectra. The present study is the first quantitative comparison of these two methods for temperature determination in flames burning at pressures up to 1 bar. The resulting temperatures showed good agreement.     

基于迭代逼近算法的土壤中机油和柴油混合物荧光信号重叠特性研究（英文）

随着我国经济的迅速发展,石油制品需求量与日俱增,伴随着工农业生产活动,大量石油制品进入土壤,造成严重的土壤石油污染。土壤中的石油污染物会对植物生长产生危害,并通过食物链威胁人类健康,因此需对土壤中的石油污染物进行现场、快速检测。激光诱导荧光技术(Laser-Induced fluorescence, LIF)具有检测速度快、灵敏度高、可现场检测等优点,但在检测土壤中有机污染物时,面临着荧光光谱重叠严重等问题。为了研究土壤中机油和柴油混合物荧光信号的重叠特性,制备了10种含有不同浓度机油、柴油混合物的土壤样品。通过搭建LIF实验系统,获取不同混合浓度的机油和柴油的荧光光谱,对油类荧光光谱进行了最大值归一化处理,建立土壤中机油、柴油混合光谱的反演关系,以最小残差平方和为指标,使用迭代逼近算法计算出土壤荧光光谱中柴油和机油样品的荧光贡献率。分别使用了全谱法和截取特征光谱两种方法计算机油和柴油的荧光贡献率。全谱法是在混合油样的全波段光谱(200~600 nm)范围进行迭代逼近,截取特征光谱方法是在截取油样光谱(330~460 nm)段进行迭代逼近。(330~460 nm)范围内包含了混合油样的所有光谱特征。用计算出的机油的荧光贡献率与机油样品浓度做线性拟合时发现,截取特征光谱法的拟合系数R为0.989,优于全谱法的0.923。分别用全谱法、截取特征光谱法计算出的荧光贡献率以及归一化机油、柴油光谱合成混合油归一化光谱,与实际归一化混合光谱比较,截取特征光谱法计算的平均相对误差为3.38%,优于全谱的8.79%,其原因是全谱法比截取特征光谱法引入了更多的噪声信号,所以在计算油类荧光贡献率时产生了较大的误差。选取机油和柴油归一化光谱上300, 350, 400, 450和500 nm等5个位置的荧光强度与归一化混合油光谱做多元线性回归拟合,计算出平均相对误差为10.31%。结果表明截取特征光谱方法优于多元线性回归方法;土壤中机油和柴油的荧光贡献率与自身的浓度之间成良好的线性关系,说明在土壤中机油和柴油混合后各自的化学性质保持稳定,在土壤中的荧光信号重叠特性是线性叠加的。这种这种方法同样可以用于其他石油类混合物的解离。通过该研究提高了LIF技术在土壤中石油烃类污染物定性与定量检测的准确性。为土壤中石油烃现场快速检测提供了方法支撑。     

不同水体中溶解有机物的荧光光谱特性研究

用激光诱导荧光(laser induced fluorescence, LIF)方法对几种不同水体中溶解有机物(dissolved organic matter, DOM)的荧光光谱进行了测量和分析,给出了不同浓度腐殖酸的归一化荧光强度与浓度的关系。结果表明, 可用此种方法进行有效的水体质量监测。     

Two-Photon Laser-Induced Fluorescence Spectra of Argon in a Grimm-Style Glow Discharge Tube

Two-photon excited laser-induced fluorescence (LIF) spectra of argon atom were successfully observed in a Grimm-style glow discharge tube, which has widely been applied to depth profiling of the elemental composition on various film-like samples by emission spectrometry. The LIF signal of an argon atomic line at 641.63 nm was observed when the glow discharge argon plasma was illuminated by a pulsed Ti:sapphire laser radiation of 7–10 mJ/pulse at 753.39 or 795.66 nm without focusing of the laser beam.     

激光诱导荧光快速直接检测土壤中多环芳烃污染物的可行性研究

提出了快速直接对土壤中多环芳烃污染物进行荧光检测的方法——激光诱导荧光光谱技术,以多环芳烃蒽为研究对象,实验验证了激光诱导荧光光谱技术快速检测土壤中蒽污染物的可行性.采用AvaSpec-2048TEC型热电制冷式光纤光谱仪对土壤中的蒽进行直接测量,研究结果表明:当土壤中蒽浓度在一定范围内(0.000 005～0.001...     

REMPI as a tool for studies of OH radicals in catalytic reactions

2 +? O₂→H₂O on polycrystalline Pt foils has been studied by detection of desorbing OH radicals using the Resonance Enhanced Multiphoton Ionization, REMPI, technique. The measurements were performed at catalyst temperatures of 1000–1400 K and a total pressure below 10^-4 mbar. The studies of OH desorption by REMPI were achieved using a two-photon excitation D²Σ^-–X²Π (1–0), followed by one-photon ionization. The ions were detected in a time-of-flight mass spectrometer, TOF-MS, in order to avoid interference from non-resonantly ionized molecules. By applying TOF-MS, a simultaneous non-resonant ionization and detection of H₂, O₂ and H₂O was achieved. Recorded REMPI spectra were compared with spectra simulated using known molecular constants. The kinetics of the reaction derived from the measurements were compared with what was obtained in earlier LIF detection of OH, performed at higher total reactant pressure using the A–X transition. REMPI TOF-MS is shown to be a complement to LIF for reaction studies below 5×10^-4 mbar total pressure, where LIF is too insensitive for quantification. The reaction kinetics was found to be in agreement with a theoretic model and previous LIF studies. Received: 8 March 1996/Revised version: 4 October 1996     

Toluene laser-induced fluorescence for in-cylinder temperature imaging in internal combustion engines

A single-laser single-camera imaging technique was demonstrated for in-cylinder temperature distribution measurements in a direct-injection internal combustion engine. The single excitation wavelength two-color detection technique is based on toluene laser-induced fluorescence (LIF). Toluene-LIF emission spectra show a red-shift with increasing temperature. Temperature can thus be determined from the ratio of the signal measured in two separate wavelength ranges independent of the local tracer concentration, laser pulse energy, and the intensity distribution. An image doubling and filtering system is used for the simultaneous imaging of two wavelength ranges of toluene LIF onto the chip of a single camera upon excitation at 248 nm. The measurements were performed in a spark-ignition engine with homogeneous charge and yielded temperature images with a single-shot precision of approximately ±?6%.     

Bacteria Spectra Obtained by Laser Induced Fluorescence

Laser-induced fluorescence technique (LIF) is described for getting bacteria spectra in the liquid phase. An excimer laser pumping a dye-laser and a doubly frequency laser have been used, exciting the bacteria to 290 nm, and using a monochromator, 600 lines/mm grating, with a CCD to measure and obtain the fluorescence spectra. In this study, a laser induced fluorescence system to measure certain bioaerosols (bacteria) was optimised. Finally, a small bacteria fluorescence spectra collection is presented.     

Quantitative measurement of naphthalene in low-pressure flames by jet-cooled laser-induced fluorescence

We have recently developed a new laser based set-up (Jet-Cooled Laser-Induced Fluorescence) for the analysis of aromatic compounds generated in flames. This method relies on the extraction of the species from the flame via a thin microprobe and their direct analysis inside a supersonic free jet by Laser-Induced Fluorescence (LIF). Under the supersonic conditions of the jet, the vibronic spectra of the molecules become structured as the possibility of electronic transitions is reduced, allowing their selective detection by LIF. In addition, due to the very low quenching efficiency inside the jet, LIF signals can be directly related to the population of the probed species and easily calibrated into absolute concentrations. All of the work presented here has been carried out for naphthalene, which is an important PAH involved in soot formation mechanisms. The calibration procedure is described in detail. We also report a detailed study of the quantitative features of the technique, in particular cooling efficiencies and collision rates as well as some additional potential factors that could bias the quantitative aspect of the method. Finally, the possibilities of the technique for the measurement of PAH within flames in the presence of soot particles along with its accuracy and reproducibility are demonstrated by recording naphthalene mole fractions profiles in several rich CH₄/O₂/N₂ flames. A detection limit of the order of a ppb is demonstrated under flame conditions with and without the presence of soot particles.     

Two-step excitation of Rb atoms on He nanodroplets

We present the first sequential laser excitation of atom-doped helium nanodroplets. Rubidium atoms on the surface of helium nanodroplets are selectively excited with a continuous wave laser to the 5²P_1/2 state so as not to desorb from the nanodroplets. From there they are excited by a laser pulse to the 5²D state; a laser-induced fluorescence (LIF) spectrum is recorded by monitoring the 6²P ?\rightarrow 5²S_1/2 emission. The LIF spectrum differs from that of the two-photon one-color direct excitation spectrum 5²D ?\leftarrow 5²S_1/2, indicating that the system does relax vibrationally during the lifetime of the 5²P_1/2 state. To model the LIF spectra we use calculated energy levels of the Rb atom as a function of its distance R from the center of the helium nanodroplet. The Franck-Condon factors of the resulting potential energy curves agree with the experimental spectra. In the future the 5²P_1/2 state can be used as a springboard to reach high-lying ²S and ²D states, and possibly create an artificial super-atom.     

Measurement of chlorophyll in water based on laser-induced fluorescence spectroscopy: Using spiral-wound unclad optical fiber system and partial least squares regression

The feasibility of laser-induced fluorescence (LIF) method for chlorophyll concentration determination in water was investigated in this study. The chlorophyll fluorescence spectra were received by a spiral-wound unclad optical fiber system. Baseline and smoothing correction methods were studied. Statistical equations were established between reference data and fluorescence spectra by linear regression and partial least squares (PLSs) regression. The PLS regression outperformed linear regression by higher correlation coefficient of 0.9996063 and root mean square error value of 0.0221807. Based on the results, it was concluded that laser-induced fluorescence method with a spiral-wound unclad optical fiber system was suitable for chlorophyll concentration determination in water, and PLS regression was a reliable method for fluorescence spectra analysis.     

Laser-induced fluorescence monitoring of the gas phase in a glow discharge during reactive sputtering of vanadium

Processes in the gas phase of a glow discharge during diode and magnetron reactive sputtering of vanadium in an Ar–O₂ atmosphere have been investigated by laser-induced fluorescence (LIF) as a function of the parameters of the glow discharge and the composition of the atmosphere. The intensity of the fluorescence spectra increased by 1.5–2.0 orders of magnitude in the magnetron sputtering process compared with that of diode sputtering. Under continuous sputtering conditions, the dependences of the intensities and relative compositions of the fluorescence spectra on the discharge parameters (discharge voltage and current) have been investigated. In pulsed mode of the glow discharge, the dynamics of changes in the spectra have been studied versus variations in the discharge duration and the lag time for recording the fluorescence signal. The dependence of the spectral line intensities on the partial pressure of oxygen has been found for vanadium and its oxide. The cathode surface at pressures of 0.03–0.04 Pa was shown to convert to the oxidized state.     

水体溶解有机物的激光诱导荧光与浊度的激光散射实验研究

以Nd：YAG的二倍频532 nm激光为激发光源,用激光诱导荧光(LIF)方法对几种不同水体中溶解有机物(DOM)和叶绿素a(Chl-a)的荧光光谱进行了测量和分析;并以水体对532 nm激发光的散射进行了水体浊度特性的研究,给出了散射光强度与浊度的关系曲线;研究结果表明,用此种方法测量水体浊度和污染物浓度可对水体质量进行有效的监测。     

Fluorescence quantum yield of carbon dioxide for quantitative UV laser-induced fluorescence in high-pressure flames

The fluorescence quantum yield for ultraviolet laser-induced fluorescence of CO₂ is determined for selected excitation wavelengths in the range 215–250 nm. Wavelength-resolved laser-induced fluorescence (LIF) spectra of CO₂, NO, and O₂ are measured in the burned gases of a laminar CH₄/air flame (φ=0.9 and 1.1) at 20 bar with additional NO seeded into the flow. The fluorescence spectra are fit to determine the relative contribution of the three species to infer an estimate of fluorescence quantum yield for CO₂ that ranges from 2–8×10^?6 depending on temperature and excitation wavelength with an estimated uncertainty of ±0.5×10^?6. The CO₂ fluorescence signal increases linearly with gas pressure for flames with constant CO₂ mole fraction for the 10 to 60 bar range, indicating that collisional quenching is not an important contributor to the CO₂ fluorescence quantum yield. Spectral simulation calculations are used to choose two wavelengths for excitation of CO₂, 239.34 and 242.14 nm, which minimize interference from LIF of NO and O₂. Quantitative LIF images of CO₂ are demonstrated using these two excitation wavelengths and the measured fluorescence quantum yield.