APPLICATIONS OF LASER-INDUCED EMISSION SPECTRAL-ANALYSIS FOR INDUSTRIAL-PROCESS AND QUALITY-CONTROL

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 x 10(8)-5 x 10(9) W cm-2), focused onto the solid or liquid sample surface in an ambient gas atmosphere of normal pressure (focus area almost-equal-to ablation area, 0.1-6 mm2), produces a hot bright plasma (early electron temperatures, 20 000-30 000 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%.