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Single, double and multiple Q-switch Nd:YAG laser pulses are used to vaporize material from solid steel samples and to induce a plasma. The material ablation of different pulse bursts, emission intensities of iron lines and electron temperatures and densities are determined. Material ablation is found to increase with multiple pulses compared to single pulses of fixed total energy as well as electron temperatures and densities. Line intensities can be increased by a factor of about two using double pulses. Quantitative microchemical analysis of low-alloy steel is performed with single and double pulses. The analytical performance is improved by the double-pulse technique.

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Laser-induced breakdown spectrometry (LIBS) with multiple pulse excitation has been applied for the multielemental analysis of steel samples in the vacuum ultraviolet. The emission of the induced plasma was coupled into a Paschen-Runge spectrometer equipped with photomultipliers linked to high-speed multichannel signal electronics. Time-resolved signal evaluation yields a significantly improved signal-to-noise ratio for the plasma emission periods after a multi-pulse excitation. Reference materials for low-alloy steel grades were used to calibrate the measurements. The investigations concentrated on the light elements phosphorus, sulfur, and carbon using emission wavelengths in the range from 178.28 nm to 193.09 nm. For the first time, limits of detection below 10 μg/g were achieved for the light elements phosphorus, sulfur, and carbon using LIBS. With these results the basis is established for future on-line applications of LIBS in the steel industry.

Significant improvements to the analytical performance of laser-induced breakdown spectrometry (LIBS) were achieved by the use of laser double pulses to ablate and excite the sample material to be analysed. To clarify the underlying physical phenomena the dynamics of the laser-induced plasma in air is studied using a high-speed electro-optic camera to observe the spatial and temporal development of the plasma geometry. A Mach-Zehnder interferometer was set-up to detect the spatio-temporal changes of the refractive index of the plasma. The velocities of the luminous plasma front and shock waves after the impact of the first laser pulse are consistent with the prediction of Sedov's model for spherical expansion. The dynamics caused by the second laser pulse of the double pulse differ significantly, indicating a modified state of the local atmosphere in the interaction region. Electron densities determined interferometrically amount to about 3 x 10(exp18) cm-3 at the center of the hemispheric plasma geometry at a delay time of 2 µs. Whereas the electron density for single or double pulses is approximately the same, the volume of the plasma is greater by more than a factor of 3 after the interaction with the double pulse of the same total energy