| Abstract |
Laser Induced Breakdown Spectroscopy (LIBS) is nowadays recognized as a highly versatile technology for materials analysis, enabling in very short times and with minimal sample preparation, simultaneous analysis of many elements of the periodic table under atmospheric pressure conditions. An attractive feature of LIBS technology is portability, which implies that it is not necessary to collect and transport samples to a laboratory. Despite these advantages, a number of unresolved issues still exist, that prevent LIBS from achieving high levels of accuracy and precision as well as sensitivity. Therefore, understanding in detail basic processes involved in LIBS measurements, ranging from the interaction of laser pulses with matter to plasma formation, expansion and optical emission, is necessary in order to achieve optimum analysis results.
In the present work, we investigate the dynamics of a nanosecond laser induced plasma plume, on an Aluminum sample, in air at atmospheric pressure by use of time-resolved imaging and spectroscopy. We study the temporal evolution of the plasma plume and the influence of the laser pulse energy on its spatial profile and optical emission intensity. Results show the Aluminum plume exhibiting an increase in the intensity corresponding to Aluminum emission, as pulse energy is increased. This is followed by a rather abrupt decrease of intensity before resuming a new increasing trend. Furthermore, the imaging studies reveal a clear vortex-type of behavior for the Aluminum plume near the target which is best observed at relatively late delay time (1000 ns) and for pulse energy values corresponding to the intensity decreasing regime. On the other hand, the Oxygen emission in the plume shows a continuous increase with pulse energy, while it is seen that the Oxygen plume tends to enclose the Aluminum one, a strong indication of air ionization at the plasma front. Simultaneous spectroscopic measurements are in agreement with the plume imaging results. In addition, emission lines from the minor elements in the Aluminum alloy exhibit the same behavior in the specific energy interval. The findings of this study are valuable for establishing optimum experimental conditions for metal alloy analysis with the LIBS technique.
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Spectroscopic imaging dynamics of laser induced plasma
