Laser‐induced Breakdown Detection (LIBD) for the Highly Sensitive Quantification of Aquatic Colloids. Part II: Experimental Setup of LIBD and Applications

Laser‐induced Breakdown Detection (LIBD) enables the concentration and size of aquatic nano‐particles (colloids), in the range of 10–1000 nm and from about 1 ng/L (ppt) up to some mg/L (ppm), to be determined. Such particles, which are frequently encountered in aquatic systems, cannot be detected using methods based on laser light scattering or obscuration or if detection is possible, then only at a comparably low level of accuracy. The method of Laser‐induced Breakdown Detection uses a high‐energy pulsed laser beam to selectively generate a plasma (dielectric breakdown) on particles. The method is based on non‐linear optics and allows for the determination of both mean particle size and concentration in aqueous samples. Practically, this method is non‐invasive, sample preparation is not required, and measurement can take place online. This second part of the double publication describes the experimental basics as well as the latest developments in the field of LIBD. Furthermore, it shows examples of practical applications and compares the technology to standard methods like dynamic laser light scattering as well as laser light obscuration.     

Influence of laser beam characteristics and focusing optics on optical laser-induced breakdown detection

Laser-induced breakdown detection (LIBD) is a well established technique for measuring size and concentration of inorganic colloids in liquids. However, most applications of LIBD are restricted to the measurement of mean sizes, which is problematic in cases of wide colloid size distributions (PSD) as typically is the case in natural systems. Evaluation of PSDs from LIBD is possible but requires detailed control of the power density within the laser focus. In the present work we describe the mathematical treatment how to calculate this power density from the beam characteristics of the light source and the optical properties of the focusing optics. The results are compared to measured spatial distributions of breakdown events of three LIBD setups.     

Total reflection x‐ray fluorescence analysis—a review

Total reflection x‐ray fluorescence analysis (TXRF) is a special energy‐dispersive x‐ray analytical technique extending XRF down to the ultra trace element range. Detection limits of picograms or nanograms per gram levels are reached with x‐ray tube excitation. Using synchrotron radiation as excitation source, femtogram levels are detectable, particularly important for Si wafer surface analysis. TXRF is specially suited for applications in which only a very small amount of sample is available, as only a few micrograms are required for the analysis. In this review, an overview of theoretical principles, advantages, instrumentation, quantification and application is given. Chemical analysis as well as surface analysis including depth profiling and thin‐film characterization is described. Special research results on extension to low‐Z elements, excitation with synchrotron radiation and x‐ray absorption spectroscopy (XAS) for chemical speciation at trace levels are reviewed. Copyright © 2007 John Wiley & Sons, Ltd.     

液相基质中重金属元素激光诱导击穿光谱实验参数的优化

针对混合溶液中重金属元素的激光诱导击穿光谱(LIBS)测量系统,为提高测量系统的检测灵敏度,以提高混合溶液中Ca和Cr金属元素LIBS光谱线强度的信噪比为目标,对LIBS测量系统中的激光脉冲能量、液相样品流速、ICCD门宽、延时等实验参数进行了优化,得到最优化参数激光脉冲能量、样品流速、ICCD门宽、延时分别为35 m J、30 ml/min、1400 ns和2400 ns,为降低LIBS技术应用于混合溶液中痕量重金属元素的检出限提供了实验参数支撑.     

Electrically induced flows in the vicinity of a dielectric stripe on a conducting plane

We report a theoretical and experimental study of the hydrodynamic flow induced by an a.c. electric field in the vicinity of a dielectric stripe deposited on a conducting plate. In the theoretical part, we model the stripe as a small change of the surface capacitance of the plate, and a perturbative approach is used to perform the calculations. This approach predicts an outwards rectified electro-osmotic slip along the surface that generates two steady counter-rotating rolls, the size of which decreases with the frequency. In the experimental section, we use tracers to determine the structure of the flow and investigate its dependence on the frequency and the amplitude of the applied voltage. The structure and amplitude of the observed flow compares satisfactorily with the theoretical analysis. This could guide the design of surface-controlled flows and help to understand the collective behavior of colloids near electrodes. Received 20 June 2002 RID="a" ID="a"e-mail: nadal@crpp.u-bordeaux.fr     

相互作用体系的极化率与拉曼光谱

分子的大多数光学性能取决于它的极化率和超极化率，例如折射率、旋光、Ｒａｙｌｅｉｇｈ和Ｒａｍａｎ散射、电光、磁光和非线性光学性能等［１］。分子间相互作用对于物质的性质有着深刻影响［２］，对于分子极化率及其有关的性能也是如此３］。本文在拉曼光谱强度理论（...     

Raman and SERS study on cimetidine–metal complexes with biomedical interest

Cimetidine (cim) is one of the most potent histamine H₂‐receptor antagonists for inhibiting excessive acid secretion caused by histamine; it has been hypothesized that the therapeutic effects can be related to its interactions with metal ions. Raman spectra of the solid cim with Co(II), Cu(II), Ni(II) and Zn(II) metal complexes show that they can adopt two different structures: one is octahedral and the other, with Zn(II), is probably tetrahedral. The octahedral structure appears to be distorted both by the different metal ions as well as by the different anion present. The study was extended to very dilute solutions (ppm range) by using the surface‐enhanced Raman scattering (SERS) technique, mimicking the physiological concentrations of cim and its metal complexes. SERS spectra suggest that, upon the binding of cim to silver colloids, the formation of stable 1:2 cim–metal complexes is excluded, the formation of 1:1 adduct appearing more probable; in this product the metal reaches its total coordination shell by complexion with water molecules. To better explain the binding mechanism of cim to a metal (Ag) surface, we performed theoretical B3LYP calculations on cim alone as well as on cim bonded to an Ag₂ metal cluster in presence of water, observing a sufficiently good agreement between experimental and theoretical wavenumbers. Copyright © 2010 John Wiley & Sons, Ltd.     

便携式激光生化探测仪

便携式激光生化探测仪采用LIBS(Laser Induced Breakdown Spectroscopy),即激光诱导击穿光谱分析技术。用一束短脉冲激光聚焦到被测样品上,产生局部等离子体,样品物质的电子跃迁至高能态,返回初始能态时会发出特定光谱辐射,每一种物质都对应各自的特征光谱。用高分辨率光谱仪对该光谱进行适时在线快速分析,在几秒钟内就可以得到被测物质的成分和浓度,可在现场对各种不明固体(炭疽杆菌等有害生化物质)、液体(如有毒饮料)、气体(如各种挥发物,即神经毒气弹等)等生化物进行在线快速探测和辨别。     

银纳米颗粒对胆固醇荧光的增强效用研究

在传统荧光光谱技术的基础上,结合金属纳米颗粒的增强荧光技术,探索提高荧光光谱技术检测人全血溶液中胆固醇含量的精度和分辨率的方法。实验研究方面,采用波长为407 nm的激光作为激发光,照射加入一定量银纳米颗粒作为荧光增强剂的人全血溶液,研究了银纳米颗粒对人全血溶液在可见光波段的荧光增强作用。结果表明,胶体状态的银纳米颗粒可以显著增强低浓度的人全血溶液荧光光谱的强度,且不同位置荧光发射峰的荧光增强效率随银胶加入量的增加均呈现先增后减的趋势,但不同峰位置的最强增强效率对应的银胶加入量不同。理论分析方面,根据实验结果及胆固醇分子和银纳米颗粒在溶液中的分布情况,建立了分子间距模型,并根据模型计算得出胆固醇分子和银纳米粒子之间的最佳增强荧光效果间距在12.19～25 nm范围内,这个结果和其他文献中的理论值吻合较好。综上所述,使用银纳米颗粒可实现全血溶液荧光的增强,研究结果为提高检测血液中多种物质的灵敏度和精度提供了有价值的参考作用。     

Single Pulse-Laser Induced Breakdown Spectroscopy in aqueous solution

In this paper the flexibility of Laser Induced Breakdown Spectroscopy (LIBS) has been proved for the analysis of water solutions. The plasma is generated directly in the bulk of a water solution by a Q-switched Nd:YAG laser (1064). The emission signal of four different solutions has been studied: AlCl₃, NaCl, CaCO₃ and LiF. The basic mechanisms influencing the emission signal and the experimental tricks for the optimization of the detection mode have been pointed out. PACS 52.70.Kz; 52.80.Wq; 39.30.+p     

激光刻蚀银胶的制备及其SERS应用

激光刻蚀技术制备金属胶体是一种新兴的表面增强拉曼散射(SERS)活性衬底制备方法,本文利用激光刻蚀技术制备了'化学纯'银胶,并通过透射电镜、吸收光谱、表面增强拉曼散射光谱等手段对其进行研究,结果表明:银胶的等离子体共振吸收峰位于396nm;银粒子分布比较均匀,多数为球形颗粒,颗粒大小在20nm左右,并且有很好的分散性;吡啶的SERS谱分析显示此银胶具有很好的增强效果。     

Nonstoichiometric laser materials: Designer wavelengths in neodymium-doped garnets

The tunable nature of lasers provides for a wide range of applications. Most applications rely on finding available laser wavelengths to meet the needs of the research. This article presents the concept of compositional tuning, whereby the laser wavelength is designed by exploiting nonstoichiometry. For research where precise wavelengths are required, such as remote sensing, this is highly advantageous. A theoretical basis for the concept is presented and experimental results in spectroscopic measurements support the theoretical basis. Laser operation nicely demonstrates the validity of the concept of designer lasers.     

Modeling of laser induced breakdown spectroscopy for very low-pressure conditions

Laser Induced Breakdown Spectroscopy (LIBS) can be considered as a prominent technology for compositional analysis of materials in low-pressure space applications. In space applications, usually LIBS is conducted in a low-pressure environment and proper understanding of the plasma parameters is significant for any improvement in the system. A model is developed to describe the heating and subsequent melting, vaporization and ionization of a target material during LIBS process. A numerical model based on one-dimensional thermal conductivity equation is being used to simulate the target evaporation and a hydrodynamic model is used to simulate plume expansion. Further, an experimental approach of measuring spectral emission from the ablation plume using emission spectroscopy and estimating the plasma state, such as the ionization species, and average plasma temperature, is investigated. An important result of this work is that for different ambient conditions, laser ablation plume dynamics can be estimated.     

Phase diagrams of electric-field-induced aggregation in conducting colloidal suspensions

To develop a theory for electric-field-driven phase transitions in concentrated suspensions, we extended our microscopic theory [Phys. Rev. E 52, 1669, (1995); 54, 5428, (1996)] beyond the dilute regime. Based on the model of the Maxwell-Wagner interfacial polarization of colloids, our theory overcomes the limitations of Brillouin's formula for the electric energy of conducting materials which is applicable only for negligibly small energy dissipation and slow time variations of the field. We found that the phase diagrams of "the particle concentration vs the electric field strength" for colloids are similar to the phase diagrams for the first-order phase separation in quenched conventional binary systems with a high-temperature miscibility gap. This explains why a variety of colloids exhibit similar field-induced aggregation patterns. Our theory provides a reasonable interpretation of the available experimental data on field-induced aggregation phenomena in electrorheological fluids and aqueous suspensions, whereas currently used theoretical models are in variance with many of the data. The theoretical results enable one to trace how the variations of the electrical properties of the constituent materials influence the topology of the suspension phase diagram and to evaluate the effects of the field strength and frequency on the particle aggregation.     

A theoretical analysis of laser flowmeters

This paper gives a unified theoretical analysis of Laser Doppler systems covering both the optical and electronic aspects, and applicable to all systems which have either a real or virtual fringe pattern. Previous experimental results by Greated for the Doppler spectrum are confirmed and in addition a fuller treatment of the low frequency part of the spectrum is presented.     

Na_2SO_4溶液激光拉曼/激光诱导击穿光谱联合探测

光谱技术应用于海底极端环境下多参数、多相态、无接触探测已成为深海化学传感器发展的一个重要方向,尤其是水下激光拉曼光谱技术和水下激光诱导击穿光谱技术正成为目前研究开发的热点。该工作旨在探索一项水下激光诱导击穿光谱与激光拉曼光谱(LIBS-LRS)联合探测技术,以实现LIBS和拉曼两种检测技术在检测系统上的整合,在信息获取上的互补。在实验室搭建了一套LIBS-LRS联合探测装置,该装置对于拉曼和LIBS采用同样的激发光源、光谱仪和探测器,前置光路分为两部分:拉曼光路和LIBS光路,分别收集Na_2SO_4溶液的拉曼信号和LIBS信号。前置光路收集的拉曼和LIBS信号由Y型光纤导入光谱仪,分别在面阵CCD不同区域进行探测。利用该装置对配置的Na_2SO_4溶液进行探测,同时获得了Na元素的LIBS信号和SO~(2-)_4拉曼信号。另外,随着激光能量的提高,在532nm脉冲激光能量超过3.6mJ时,在拉曼光路同时获得了Na元素的LIBS信号和SO~(2-)_4拉曼信号,这样采用同一光路即可实现两种光谱技术的联合,然而实验发现,随着激光能量的增加,激光在溶液中击穿产生的轫致辐射造成了光谱探测基线整体的抬升,对拉曼光谱弱信号的探测是不利的。实验结果初步证明了在拉曼和LIBS在水下联合探测的可行性。     

The Study of the Behaviors of Zinc and Strontium in Caries-Affected Teeth by Laser-Induced Breakdown Spectroscopy(LIBS) Technique

We report on the application of Laser Induced Breakdown Spectroscopy(LIBS)technique to the study of Ca,P,Zn and Sr evolutions for adult caries-affected teeth using nanosecond laser pulses.The aim of this work is to better understand the behaviors of Zn and Sr as trace-elements in the caries eruption with respect to the behaviors of one of the main compounds of the hydroxyapatite crystal which is the calcium.The study was focused on the investigation of these elements’evolutions from three parts of the enamel surfaces of twenty two adult caries-affected teeth;the healthy part,the dental plaque part and the caries-affected part.The decrease rates of Zn,Sr and P was,also,compared to the Ca one.Comparison concerned normalized emission line intensities.For every species,normalization was done relatively to the emission line intensities of the healthy part.Results showed that abundances of these elements decrease similarly from the healthy parts to the affected-caries parts.The higher decrease rate was noticed for the calcium.The evolutions of Zn and Sr for the three parts of the teeth surfaces cannot inform about the substitution of the calcium by these trace-elements,however the comparison of their decrease rates to the calcium one can be considered as a valuable index of this substitution.     

Near field induced defects and influence of the liquid layer thickness in Steam Laser Cleaning of silicon wafers

The removal of particles from commercial silicon wafers by Steam Laser Cleaning was examined. Polystyrene colloids were used as model contaminants due to their well defined size and shape. In contrast to previous studies, where the experimental conditions on the surface were only roughly determined, special care was taken to control the amount of liquid applied to the surface. We report measurements of the cleaning threshold for different particle sizes. The comparability of the results was ensured by the reproducible conditions on the surface. Moreover, we studied the influence of different liquid film thicknesses on the cleaning process. Investigations of laser induced liquid evaporation showed that the cleaning threshold coincides with the fluence necessary for the onset of explosive vaporization. After particle removal, the surface was examined with an atomic force microscope. These investigations demonstrated that near field enhancement may cause defects on the nm-scale, but also showed that Steam Laser Cleaning possesses the capability of achieving damage-free removal for a large range of different particle sizes. Received: 14 January 2003 / Accepted: 16 January 2003 / Published online: 28 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-7531/88-3127, E-mail: florian.lang@uni-konstanz.de     

Laser ablation of copper based alloys by single and double pulse laser induced breakdown spectroscopy

Single and double pulse laser induced breakdown spectroscopy was applied to the analysis of copper based alloys samples, in order to investigate the material ablation process under two different experimental conditions. An Nd:YAG laser, emitting at the fundamental wavelength (1064 nm) for a fixed value of total energy with the same pulse width, has been used for both set-up configurations. Certified samples of copper based alloys were examined in order to investigate the effect of their different compositions on the ablation process efficiency. The craters produced by the laser on the samples surfaces were measured by a contact profilometer in order to evaluate the mass of ablated material. In this respect the differences in behaviour of the single and the double pulse ablation for Laser Induced Breakdown Spectroscopy (LIBS), respectively, have been considered. The dependence, under the same experimental conditions, of the LIBS background emission of the different ablated masses of the material has also been investigated, by looking for normalization algorithms for quantitative data reduction.The behaviour of some peculiar intensity ratios, suitable for building calibration curves, has been studied in order to evaluate the trend in fractionated evaporation on going from the single pulse to the double pulse technique. PACS 52.70.-m; 52.50.Jm; 42.62.Fi     

Laser‐pump/X‐ray‐probe experiments with electrons ejected from a Cu(111) target: space‐charge acceleration

A comprehensive investigation of the emission characteristics for electrons induced by X‐rays of a few hundred eV at grazing‐incidence angles on an atomically clean Cu(111) sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation (high peak current of photoemission) on the properties of Auger and photoelectrons liberated by a probe X‐ray beam is investigated in time‐resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space‐charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical results.