B. W. Smith

Fundamentals and Applications of Laser-Induced Breakdown Spectroscopy

Abstract Laser-induced breakdown spectroscopy is reviewed by dividing the literature into three categories according to target phase: solid, liquid, or gas. Within each category, the literature is ...

Trace Determination of Mercury: A Review

Abstract Methods used for trace (sub-ppm) detection of mercury are reviewed. Included are spectrometric methods such as atomic absorption, fluorescence, emission, and mass spectrometry; electrochemical methods; and as radiometric methods as well as other common and novel techniques. Limits of detection are reported where given, and advantages and disadvantages are compared.

Variables Influencing the Precision of Laser-Induced Breakdown Spectroscopy Measurements

Several factors influence the precision of laser-induced breakdown spectroscopy (LIBS) measurements. This paper reports on the effect of emission signal temporal development, sample translational velocity, number of spectra accumulated, laser pulse stability, detector gate delay, surface roughness, and use of background correction on LIBS precision. The results are presented in two formats: within measurement/shot-to-shot precision (intra-measurement) and between measurement precision (inter-measurement). The data indicate that intra- and inter-measurement precision are optimized under different conditions. The best precision obtained was 0.03%.

Laser induced breakdown spectroscopy as a tool for discrimination of glass for forensic applications

Materials analysis and characterization can provide important information as evidence in legal proceedings. The potential of laser induced breakdown spectroscopy (LIBS) for the discrimination of glass fragments for forensic applications is presented here. The proposed method is based on the fact that glass materials can be characterized by their unique spectral fingerprint. Taking advantage of the multielement detection capability and minimal to no sample preparation of LIBS, we compared glass spectra from car windows using linear and rank correlation methods. Linear correlation combined with the use of a spectral mask, which eliminates some high-intensity emission lines from the major elements present in glass, provides effective identification and discrimination at a 95% confidence level.

Effective normalization technique for correction of matrix effects in laser-induced breakdown spectroscopy detection of magnesium in powdered samples

The goal of this research was to investigate the influence of the matrix on the laser-induced spectroscopy of magnesium. Powdered samples were used and were presented to the measurement as thin distributions on adhesive tape. A wide range of NIST certified reference materials were used as samples. With careful sample preparation and correction for sample surface density on the tape (determined by weighing), reasonable consistency in the Mg signal intensity was obtained regardless of sample matrix. Relative error of ∼10% and a precision of 10–20% were obtained for the determination of Mg in several certified samples.

Measurement of uranium isotope ratios in solid samples using laser ablation and diode laser-excited atomic fluorescence spectrometry

Abstract A diode laser is used for the selective excitation of 235 U and 238 U in a laser-induced plasma applying Nd:YAG laser pulses to UO 2 samples. The diode laser is rapidly scanned immediately following each laser sampling and the resonance atomic fluorescence spectrum for both isotopes is obtained on a pulse-to-pulse basis. Time-integrated measurements, with the diode laser fixed at either isotope, were also made. Optimum signal-to-noise was obtained at a distance of 0.8 cm from the sample surface, a pressure of 0.9 mbar and a Nd:YAG laser pulse energy of 0.5 mJ (880 MW cm −2 ). Three samples with 0.204, 0.407 and 0.714% 235 U were measured. For example, for the UO 2 pellet with the natural uranium isotopic composition (99.281% 238 U and 0.714% 235 U), the accuracy and precision were 7% and 5% (460 shots), respectively, limited by the continuum emission background from the laser-induced plasma.

Modeling an inhomogeneous optically thick laser induced plasma: a simplified theoretical approach ☆

Abstract A simplified theoretical approach is developed for an optically thick inhomogeneous laser induced plasma. The model describes the time evolution of the plasma continuum and specific atomic emission after the laser pulse has terminated and interaction with a target material has ended. Local thermodynamic equilibrium is assumed allowing the application of the collision-dominated plasma model and standard statistical distributions. Calculations are performed for a two-component Si/N system. The model input parameters are the number of plasma species (or plasma pressure) and the ratio of atomic constituents. Functions are introduced which describe the evolution of temperature and size of the plasma. All model inputs are experimentally measurable. The model outputs are spatial and temporal distributions of atom, ion and electron number densities, evolution of an atomic line profile and optical thickness and the resulting absolute intensity of plasma emission in the vicinity of a strong non-resonance atomic transition. Practical applications of the model include prediction of temperature, electron density and the dominating broadening mechanism. The model can also be used to choose the optimal line for quantitative analysis.

Quantitative analysis of low-alloy steel by microchip laser induced breakdown spectroscopy

The development of a compact laser induced breakdown spectroscopy (LIBS) system increases the possibilities of applying the technique in industrial arenas, field applications and process monitoring. Significant progress has been achieved in miniaturization of optical detectors and lasers, allowing portable, low-cost LIBS equipment to be devised. Conventional lasers for LIBS, like actively Q-switched Nd:YAG lasers are limited by their bulkiness, the need for a cooling system and high power consumption. The use of a miniature solid state microchip laser overcomes these drawbacks and offers further advantages of good beam quality, high pulse repetition frequency and less damage to target. In this work we studied the quantification of elemental composition of low alloy steel samples using a higher power microchip (“powerchip”) laser. The possibility of real time, in situ quantification of such materials by powerchip LIBS enhances the applicability of the technique to process monitoring in the steelmaking industry. The performance of the LIBS technique based on a powerchip laser and a portable non-intensified, non-gated detector for elemental quantification is evaluated and compared to that obtained using an intensified detector. Calibrations were achieved for Cr, Mo, Ni, Mn and Si with linear regression coefficients between 0.98–0.99 and limits of detection below 100 ppm in most cases.

Identification of particulate materials by correlation analysis using a microscopic laser induced breakdown spectrometer

The goal of this work was the instant identification of particulate geological materials by comparison with spectral libraries stored in a computer. The libraries consisted of representative spectra from different groups of powdered samples. Special attention was paid to identification of particles with very similar chemical composition, such as certain iron ores. Chemical speciation analysis was also carried out. Iron and iron oxides were shown to be reliably identified using statistical correlation methods. Both linear and rank correlations were applied. Both correlation methods yielded probabilities of correct identification close to unity for almost all studied samples. This technique should have applications in the metallurgical, mining, and semiconductor industries, and in medical, environmental and forensic sciences.

Novel uses of lasers in atomic spectroscopy. Plenary Lecture

This paper reviews several novel uses of lasers in atomic spectroscopy. A tutorial discussion is given of the basic processes involving the interaction of laser radiation with atoms and the measurement approaches. Laser microprobes, especially laser induced breakdown spectroscopy and laser ablation-inductively coupled plasma-optical emission or mass spectrometry are reviewed thoroughly with respect to principles, instrumentation and applications. Laser excited atomic fluorescence and atomic absorption spectrometry with diode lasers are considered primarily with respect to recent publications. Laser-enhanced ionization, resonance ionization and resonance ionization imaging are also thoroughly reviewed with respect to recent publications. Diagnostical measurements of plasmas and atom reservoirs are discussed. The principles of six laser based atomic absorption methods are given and the methods are compared with respect to detection limits. Finally, future uses of lasers in atomic spectroscopy and a comparison of the characteristics of various atomic methods for trace elements are given.