In-situ optical emission spectroscopy of laser-induced vanadium oxide plasma in vacuum

This study aims to analyze the elemental composition, and temporal- and spatial distributions of vanadium atoms and ions in the laser-induced vanadium oxide plasma under high vacuum using optical emission spectroscopy. Neutral atoms and singly charged V ions were detected under high vacuum in the emission spectra. The mean translational velocity of neutral V atoms in their first 25 mm propagation was estimated to be 15.7 km/s using the temporal- and spatial dynamics investigation of neutral V species in the plasma.     

Microanalysis of tool steel and glass with laser-induced breakdown spectroscopy

A laser microscope system for the microanalytical characterization of complex materials is described. The universal measuring principle of laser-induced breakdown spectroscopy (LIBS) in combination with echelle optics permits a fast simultaneous multielement analysis with a possible spatial resolution below 10 pm. The developed system features completely UV-transparent optics for the laser-microscope coupling and the emission beam path and enables parallel signal detection within the wavelength range of 200-800 nm with a spectral resolution of a few picometers. Investigations of glass defects and tool steels were performed. The characterization of a glass defect in a tumbler by a micro-LIBS line scan, with use of a 266-nm diode-pumped Nd:YAG laser for excitation, is possible by simple comparison of plasma spectra of the defect and the surrounding area. Variations in the main elemental composition as well as impurities by trace elements are detected at the same time. Through measurement of the calibration samples with the known concentration of the corresponding element, a correlation between the intensity of spectral lines and the element concentration was also achieved. The change of elemental composition at the transient stellite solder of tool steels has been determined by an area scan. The two-dimensional pictures show abrupt changes of the element distribution along the solder edge and allow fundamental researches of dynamic modifications (e.g., diffusion) in steel.     

Liquid steel analysis with laser-induced breakdown spectrometry in the vacuum ultraviolet

Laser-induced breakdown spectrometry (LIBS) with multiple pulse excitation has been applied for the multielemental analysis of liquid steel. The laser beam and the measuring radiation are guided inside a moveable lance to gain access to the melt surface from the top. Low-alloy steel grades were investigated with a focus on the light elements phosphorus, sulfur, and carbon by use of emission wavelengths in the vacuum ultraviolet. Calibration curves were determined for the elements carbon, phosphorus, sulfur, nickel, and chromium in steel melts of 100 kg. The estimated limits of detection for the light elements phosphorus, sulfur, and carbon are below 21 microg/g for direct analysis of liquid steel with LIBS. The results demonstrate the potential of the laser-based analysis to fulfill the requirements for a process integrated on-line analysis in the secondary metallurgy of steel works.     

Plasma-particle interactions in a laser-induced plasma: implications for laser-induced breakdown spectroscopy

The interaction between laser-induced plasmas and individual particles controls the rate of particle dissociation and subsequent atomic diffusion and emission processes, with implications for single-particle spectroscopy, as well as materials synthesis and other plasma sources. It is demonstrated through quantitative plasma imaging studies that discrete particles dissociate on a time scale of tens of microseconds within plasmas formed by 300-mJ Nd:YAG laser pulses. Significant spatial nonhomogeneity, as measured by localized atomic emission from particle-derived calcium atoms, persists on a comparable time scale, providing a measure of their average atomic diffusion rate of 0.04 m(2)/s. In addition, the resulting calcium atomic emission is explored using image analysis as well as traditional spectroscopic analysis.     

In situ analysis of metal melts in metallurgic vacuum devices by laser-induced breakdown spectroscopy

We report on rapid in situ analysis of liquid metal melts under reduced ambient pressure by laser-induced breakdown spectroscopy (LIBS) using a transportable system. LIBS denotes a method in which characteristic optical emission line intensities of excited species in laser-generated plasma plumes are used for a quantitative chemical analysis of target materials. It is a fast, noncontact method that can be carried out under various atmospheric conditions, allowing large working distances between the sample under investigation and the detection system. For these reasons, LIBS is applicable in particular for process control in metallurgy under reduced ambient pressure. This was demonstrated for two types of vacuum devices under production conditions at a steel mill. The results of these experiments, including calibration curves for Cr, Ni, and Mg in liquid steel, are presented. The influence of variations in the ambient pressure on the results of the LIBS analysis is discussed within the frame of a generalized shock-wave model for the expansion of the laser-induced plasma plume.     

Minimally destructive analysis of aluminum alloys by resonance-enhanced laser-induced plasma spectroscopy

Aluminum alloys were analyzed for minor components and trace impurities using double pulse resonance-enhanced laser-induced plasma spectroscopy. The first laser pulse at 532 nm ablated the sample. The second laser pulse at 396.15 nm resonantly excited the Al atoms to rekindle the plasma plume. Emissions from Mg, Cu, Si, and Na were observed. At laser energies below the damage threshold, the analyte emissions were already orders of magnitude above the background noise. Nonresonant probes of comparable sensitivity would melt and deform the sample surface. Because of the lower etch rate of resonant probes, depth profiling at nanometer resolution was possible. Using this method, the variation of [Na] with depth was measured for high-purity samples. In contrast, nonresonant probes required 5 times the fluence and proportionally poorer resolution. Worse yet, the associated heating and laser remelting modified the [Na] profile.     

Analysis of solids by laser ablation and resonance-enhanced laser-induced plasma spectroscopy

An analytical technique based on resonance-enhanced laser-induced plasma spectroscopy was demonstrated. Pellets of potassium iodate containing trace amounts of sodium were ablated by a 532-nm laser pulse in air. After 30 ns, the plasma plume was intercepted by a 404.4-nm laser pulse to resonantly photoionize the potassium atoms in the vapor plume. The 589-nm emissions of the sodium were found to be significantly enhanced. The enhancement was shown to depend critically on the profile of the 532-nm beam as well as the spatial overlap of the two laser pulses. Using this double-pulse scheme, the mass detection limit for sodium was estimated to be about 200 pg, which was five times better than that obtained by using the 532-nm laser pulse alone.     

Generation of vacuum ultraviolet radiation for precision laser spectroscopy

We report on the generation of tunable nanosecond pulsed VUV radiation near 120 nm using difference-frequency mixing in H(2). Our scheme uses two dye lasers, one fixed at 606 nm and the other tunable in the red. These convenient wavelengths simplify the metrology needed for accurate VUV laser spectroscopy. Efficient VUV generation is attained with modest Nd:YAG pump laser energies (approximately 160 mJ at 532 nm), making the scheme attractive even when narrow bandwidths are not essential.     

Formation of a cathode plasma jet in a laser-induced vacuum discharge

The process of formation of micropinch structures in the plasma of a vacuum discharge initiated by a laser pulse on the cathode is studied. It is demonstrated that the micropinch formation takes place mainly in the substance evaporated by the laser pulse upon the discharge initiation. The size of the hot region of the plasma jet and the distance from the cathode to the micropinch increase with increasing laser pulse energy.     

Process analysis of recycled thermoplasts from consumer electronics by laser-induced plasma spectroscopy

An experimental setup for direct elemental analysis of recycled thermoplasts from consumer electronics by laser-induced plasma spectroscopy (LIPS, or laser-induced breakdown spectroscopy, LIBS) was realized. The combination of a echelle spectrograph, featuring a high resolution with a broad spectral coverage, with multivariate methods, such as PLS, PCR, and variable subset selection via a genetic algorithm, resulted in considerable improvements in selectivity and sensitivity for this complex matrix. With a normalization to carbon as internal standard, the limits of detection were in the ppm range. A preliminary pattern recognition study points to the possibility of polymer recognition via the line-rich echelle spectra. Several experiments at an extruder within a recycling plant demonstrated successfully the capability of LIPS for different kinds of routine on-line process analysis.     

Direct measurements of sample heating by a laser-induced air plasma in pre-ablation spark dual-pulse laser-induced breakdown spectroscopy (LIBS)

Direct measurements of temperature changes were made using small thermocouples (TC), placed near a laser-induced air plasma. Temperature changes up to ~500 °C were observed. From the measured temperature changes, estimates were made of the amount of heat absorbed per unit area. This allowed calculations to be made of the surface temperature, as a function of time, of a sample heated by the air plasma that is generated during orthogonal pre-ablation spark dual-pulse (DP) LIBS measurements. In separate experiments, single-pulse (SP) LIBS emission and sample ablation rate measurements were performed on nickel at sample temperatures ranging from room temperature to the maximum surface temperature that was calculated using the TC measurement results (500 °C). A small, but real sample temperature-dependent increase in both SP LIBS emission and the rate of sample ablation was found for nickel samples heated up to 500 °C. Comparison of DP LIBS emission enhancement values for bulk nickel samples at room temperature versus the enhanced SP LIBS emission and sample ablation rates observed as a function of increasing sample temperature suggests that sample heating by the laser-induced air plasma plays only a minor role in DP LIBS emission enhancement.     

Influence of the laser pulse duration on spectrochemical analysis of solids by laser-induced plasma spectroscopy

Quantitative analysis of aluminum and copper alloys by means of laser-induced plasma spectroscopy (LIPS) has been investigated for three representative laser pulse durations (80 fs, 2 ps, and 270 ps). The experiments were carried out in air at atmospheric pressure with a constant energy density of 20 J/cm2. Because the decay rate of the spectral emission depends on the laser pulse duration, the optimum detection requires an optimization of the temporal gating acquisition parameters. LIPS calibration (sensitivity and nonlinearity) and the limit of detection (LOD) are discussed in detail. While the LOD of minor elements embedded in alloy samples obtained by sub-picosecond or sub-nanosecond laser pulses are both time and element dependent, provided an appropriate temporal window is chosen, the optimum LODs (several parts per million (ppm)) prove to be independent of the laser pulse duration. Finally, it is found that for elements such as those detected here, gated LIPS spectra using picosecond or sub-picosecond laser pulses provide much better LOD values than non-gated spectra.     

等离子体显示板真空紫外荧光测试系统

设计等离子体显示板(PDP)真空紫外荧光测试系统来测评PDP荧光粉的特性。系统通过巧妙设计测试腔,模拟PDP放电单元,为激发PDP荧光粉发光提供所需要的较强真空紫外线,使系统能够分析出荧光粉的光谱功率分布、发光亮度、带宽、发射谱线主峰波长、色品坐标、颜色纯度和主波长等各种光学特性。实验结果数据表明,该系统的可重复性好、精度高,为研制高质量的等离子体显示板提供了依据。     

Glass-batch composition monitoring by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy is an almost ideal technique for the in situ monitoring of the composition of a glass batch before it enters the glass-melting furnace, saving a significant amount of energy by the optimization of the furnace parameters for a particular composition of the glass batch. We investigate this application of laser-induced breakdown spectroscopy by determining the elemental composition of the glass batch used (i) as a surrogate for radioactive glass waste and (ii) to manufacture the most common type of flat glass. The surrogate glass-batch and flat-glass calibration curves for the major constituents have been prepared using both the line intensity and the line-intensity ratio. The analytical figure of merit of the glass-batch data obtained from the two different detection systems, namely, the Czerny-Turner spectrometer with an intensified diode-array detector and the echelle spectrometer fitted with an intensified CCD camera, are compared.     

Detection of uranium in solids by using laser-induced breakdown spectroscopy combined with laser-induced fluorescence

Detection of uranium in solids by using laser-induced breakdown spectroscopy has been investigated in combination with laser-induced fluorescence. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the uranium atoms and ions within the plasma plumes generated by a Q-switched Nd:YAG laser. Both atomic and ionic lines can be selected to detect their fluorescence lines. A uranium concentration of 462 ppm in a glass sample can be detected by using this technique at an excitation wavelength of 385.96 nm for resonant excitation of U II and a fluorescence line wavelength of 409.0 nm from U II.     

Helium detection in gas mixtures by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been evaluated as a tool for monitoring trace levels of helium in gas mixtures consisting mostly of hydrogen. Calibration data for helium in hydrogen was investigated at different helium concentration levels. At high concentrations of helium (>7.25%), the LIBS signal is quenched due to Penning ionization. The hydrogen alpha line (656.28 nm) was observed to broaden as the concentration of helium impurities in the hydrogen gas mixture increased. The helium line at 587.56 nm was selected as the analyte line for helium impurity detection. The effects of laser energy, the delay time between the laser pulse and data acquisition, and the gas pressure on the LIBS signal of helium were investigated to determine the optimum conditions for helium detection. The LIBS signal from the helium line at 587.56 nm shows good linear correlation with helium concentration for He concentrations below 1%. Thus, LIBS can be reliably used to detect the low levels of helium. The limit of detection for helium was found to be 78 ppm.     

Detection of bacteria by time-resolved laser-induced breakdown spectroscopy

A laser-induced breakdown spectroscopy technique for analyzing biological matter for the detection of biological hazards is investigated. Eight species were considered in our experiment: six bacteria and two pollens in pellet form. The experimental setup is described, then a cumulative intensity ratio is proposed as a quantitative criterion because of its linearity and reproducibility. Time-resolved laser-induced breakdown spectroscopy (TRELIBS) exhibits a good ability to differentiate among all these species, whatever the culture medium, the species or the strain. Thus we expect that TRELIBS will be a good candidate for a sensor of hazards either on surfaces or in ambient air.     

Rapid determination of zinc in soils by laser-induced breakdown spectroscopy

The possibility of quantitative detection of trace zinc levels in soils per single laser pulse using laser-induced breakdown spectroscopy is shown. The development of laser plasma and the signal-to-noise ratio are studied when evaporating soils by the second (532 nm) and the third (355 nm) harmonics of an Nd:YAG pulse laser. The use of the third harmonics permits one to reach the zinc detection limit (18 ppm) below Occupational Exposure Limits (OEL) in soil (150 ppm) and below the mean abundance in the earth’s crust of zinc (83 ppm). This allows the use of the suggested technique for the rapid determination of soil pollution with zinc and searching for geochemical anomalies.     

Effect of laser-induced crater depth in laser-induced breakdown spectroscopy emission features

The influence of crater depth on plasma properties and laser-induced breakdown spectroscopy (LIBS) emission has been evaluated. Laser-induced plasmas were generated at the surface and at the bottom of different craters in a copper sample. Plasmas produced at the sample surface and at the bottom of the craters were spatially and temporally resolved. LIBS emission, temperature, and electronic number density of the plasmas were evaluated. It is shown that the confinement effect produced by the craters enhances the LIBS signal from the laser-induced plasmas.