Laser-induced breakdown spectroscopy using ultrashort and dual pulses.

摘要

Laser-induced breakdown spectroscopy (LIBS) is a very simple and rapid form of elemental analysis, in which emission from a laser generated plasma is used to identify the elemental constituents of virtually any type of sample without sample preparation. Because only optical access is required, LIBS can be coupled with fiber-optics and used for remote and on-line applications. However, the use of LIBS has been limited analytically because it suffers from poor precision and sensitivity compared to other forms of elemental analysis. Recent work in our laboratory, aimed at determining the factors that lead to these disadvantages, have led our group to investigate the use of ultrashort and dual laser pulses for LIBS.; Research aimed at improving precision in LIBS, has led to study the use of 1.3 ps and 140 fs laser excitation to measure LIBS spectra. As expected, an increase in the precision of material ablated is seen using these pulses. In addition, we also see rapid decay of atomic-line and background intensities, as well as a faster plasma dissipation, suggesting that faster laser pulse rates can be used to increase the sensitivity of the LIBS measurement.; We have discovered a new pre-ablation spark dual-pulse LIBS technique that has demonstrated up to 100-fold signal enhancements as well as greatly enhanced sample ablation for many sample types. In this technique, one laser pulse is focused parallel to the sample surface forming an air spark, while another pulse is focused onto the sample microseconds later. The position of each laser pulse relative to the sample is important for maximum signal enhancements. The best enhancements are seen when both the preablation spark pulse and the ablation pulse are focused at or slightly above the sample. When the pulses are focused close to each other, better LIBS signal is also obtained.; Finally, a fiber-optic dual-pulse LIBS probe was developed to improve the detection of metals in-situ and remotely. This collinear probe, where one pulse was used to reheat the plasma formed by another pulse, demonstrated 2- to 6-fold signal enhancements for lead and copper samples.