In the twenty years of so since its inception, 'laser microspectral analysis' (LMSA) has become an established technique for rapid, spot analysis of solid targets. Since a laser is used to vaporise the sample, little or no preparation is required and analysis of dielectric and conducting samples can be performed. Only microgram quantities of about 50 mu m diameter are sampled and, as such, the technique fills the gap between electron and ion microprobes and conventional emission spectroscopy. The authors discuss the physical characteristics of laser produced plasmas, in so far as they are suitable for quantitative spectrochemical analysis, together with the instrumentation required. Some important examples of the use of this technique in both science and industry are described.
The design and use of a small time of flight (TOF) mass spectrometer for producing mass spectra of ions which have been laser ablated from a solid metal target are described. TOF spectra with a resolution m/ Delta m of 100 were produced. Known samples of inconel were used to characterize the operation of the spectrometer. Isotope separation was demonstrated and mass spectra, in which the ratios of constituents were representative of the composition of the sample, were produced. The beneficial effect of a stainless steel grid placed between the target and flight tube at a positive potential was investigated. Results are shown and correlated with theoretical flight times for different conditions. A model is proposed for the various processes occurring.
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