A commercial, 7 microJ/pulse, 550 ps microchip laser is used to induce plasma on Pb, Si, Cu, Fe, Ni, Ti, Zn, Ta, and Mo foils and a Si wafer. The measured plasma lifetime is comparable with the duration of the laser pulse (a few ns). The plasma continuum radiation is low, while some of the strong resonance lines (e.g., Zn 213.86 nm) show self-reversal. Quantitative analysis is possible using non-gated detectors but analytical lines should be chosen with care to avoid reduction in the linear dynamic range. The mass removed (0.5-20 ng/pulse) is sufficient to yield spectra that are detectable with portable grating spectrometers equipped with non-gated, non-intensified detector arrays. The spectrum of Cd is detected with a broadband portable spectrometer (200-950 nm). The combination of the broadband spectrometer and the microchip laser is very promising for material identification, especially in field applications.
Metal ablation with a short pulse, low energy microchip laser was investigated with respect to its application to laser induced breakdown spectroscopy (LIBS). Target surface modifications and crater parameters as a function of laser pulse properties were studied. The effect of the laser pulse is limited to the focal spot, but surface modification by the laser-induced plasma can extend several micrometers beyond the focal spot depending on the target's thermal properties. Mass removal per shot was found to depend upon the heat of fusion of the target, while appreciable plasma emission was observed only at high pulse energies. Plasma composition and emission intensity can change significantly with the surface properties, requiring a fresh, flat surface to be exposed to each laser pulse. Increasing the temperature of the target resulted in a corresponding increase in plasma emission due to an increased mass removal per laser shot: however, selective ablation was not observed at temperatures up to 550 1C. Fractionation was observed at low laser irradiances and inside deep craters, but it was minimal compared with the results reported for other laser ablation systems. Characteristics such as precision in the mass removal process, well-defined crater parameters, and good spatial resolution make the Powerchip laser an attractive laser sampling tool.
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