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 ...

Fundamentals and Applications of Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy has been applied to perform elemental analysis of aluminum alloy targets. The plasma is generated by focusing a pulsed Nd:YAG laser on the target in air at atmospheric pressure. Such a plasma was characterized in terms of its appearance, emission spectrum, space-integrated excitation temperature, and electron density. The electron density is inferred from the Stark broadening of the profiles of ionized aluminum lines. The temperature is obtained by using Boltzmann plots of the neutral iron lines. Calibration curves for magnesium, manganese, copper, and silicon were produced. The detection limits are element-dependent but are on the order of 10 ppm.

http://journals.sagepub.com/doi/pdf/10.1366/0003702953964408

Quantitative Analysis of Aluminum Alloys by Laser-Induced Breakdown Spectroscopy and Plasma Characterization

INTRODUCTION When a high-powered laser beam is focused onto a small area or spot of a solid surface, the temperature of the locally heated region rises rapidly to the vaporization temperature of the solid material and an optically induced plasma, frequently called a laser-induced plasma (LIP) or laser-ablated plasma (LAP) or laser spark is formed at the surface. The plasma will be formed when the laser power density exceeds the breakdown threshold value of the solid surface. Although different materials have different breakdown thresholds, an optical plasma is produced when the laser power density exceeds several megawatts per centimeter squared (106 - 109 W/cm2). This plasma has been used for sampling, atomization, excitation, and ionization in analyhcal atomic spectroscopy. It has also been frequently used and proposed as a source for atomic emission spectrometry (AES). In this case the technique is most ofien referred to as laser microprobe optical emission spectrometry (LM-OES) developed by Brech and ...

Applications of Laser-Induced Breakdown Spectrometry

In laser-induced breakdown spectroscopy (LIBS), a focused laser pulse is used to ablate material from a surface and form a laser plasma that excites the vaporized material. Geometric factors, such as the distance between the sample and the focusing lens and the method of collecting the plasma light, can greatly influence the analytical results. To obtain the best quantitative results, one must consider this geometry. Here we report the results of an investigation of the effect of sampling geometry on LIBS measurements. Diagnostics include time-resolved spectroscopy and temporally and spectrally resolved imaging using an acousto-optic tunable filter (AOTF). Parameters investigated include the type of lens (cylindrical or spherical) used to focus the laser pulse onto the sample, the focal length of the lens (75 or 150 mm), the lens-to-sample distance (LTSD), the angle-of-incidence of the laser pulse onto the sample, and the method used to collect the plasma light (lens or fiber-optic bundle). From these studies, it was found that atomic emission intensities, plasma temperature, and mass of ablated material depend strongly on the LTSD for both types of lenses. For laser pulse energies above the breakdown threshold for air, these quantities exhibit symmetric behavior about an LTSD approximately equal to the back focal length for cylindrical lenses and asymmetric behavior for spherical lenses. For pulse energies below the air breakdown threshold, results obtained for both lenses display symmetric behavior. Detection limits and measurement precision for the elements Be, Cr, Cu, Mn, Pb, and Sr, determined with the use of 14 certified reference soils and stream sediments, were found to be independent of the lens used. Time-resolved images of the laser plasma show that at times >5 μs after plasma formation a cloud of emitting atoms extends significantly beyond the centrally located, visibly white, intense plasma core present at early times (<0.3 μs). It was determined that, by collecting light from the edges of the emitting cloud, one can record spectra using an ungated detector (no time resolution) that resemble closely the spectra obtained from a gated detector providing time-resolved detection. This result has implications in the development of less expensive LIBS detection systems.

Effect of Sampling Geometry on Elemental Emissions in Laser-Induced Breakdown Spectroscopy

This review of process analytical chemistry is an update to the previous review on this subject published in 1995(A2). The time period covered for this review includes publications written or published from late 1994 until early 1999, with the addition of a few classic references pointing to background information critical to an understanding of a specific topic area. These older references have been critically included as established fundamental works. New topics covered in this review not previously treated as separate subjects in past reviews include sampling systems, imaging (via optical spectroscopy), and ultrasonic analysis.

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Process Analytical Chemistry

Laser-induced emission spectral analysis (LIESA, a registered trademark of instruments developed by Krupp), better known in the literature as laser microanalysis or laser-induced breakdown spectroscopy, is a suitable method for the direct in-process measurement of elemental concentrations in various solid and liquid materials. This method has been developed recently by Krupp for in-process quality assurance and process control in different industrial branches such as steel production and plant making. As a result several LIESA instruments have already been developed or are under development for marketing. In all cases on-line and in-process elemental analysis of materials at various stages of production yield information on the quality of the material and the fabrication process. The beam of a pulsed high-power laser (irradiance: 1 × 108–5 × 109 W cm–2), focused onto the solid or liquid sample surface in an ambient gas atmosphere of normal pressure (focus area≈ablation area, 0.1–6 mm2), produces a hot bright plasma (early electron temperatures, 20000–30000 K). The emitted plasma light is observed end-on and passes by way of an optical fibre bundle to a spectrometer, where it is detected in the focal plane by means of an optical multichannel analyser with high time resolution (on the microsecond scale). A fast computer evaluates the measured spectra and calculates the element concentrations via calibration procedures. Relative detection limits of between 10 and 100 ppm can be achieved for most of the detectable elements in various matrices (steel, rubber, rock and glass). Procedures are available to convert relative measurements with relative standard deviations of between 1 and 2% into absolute concentration values with relative accuracies of about 3%.

Ulrich Hahn

Papers

Applications of laser-induced emission spectral analysis for industrial process and quality control