What is it about?
Observation of a current neutralizing the charge occurred on a target exposed to intense laser radiation provides understanding of major phases of laser-produced plasma development processes. The target is positively charged when the most energetic electrons escape a potential barrier and leave the target definitely. The target current analysis reveals that three major phases of the target current can be distinguished. During the ignition phase, the electron emission is driven by the laser pulse and the positive charge generated on the target is balanced by electrons coming from the ground through the target holder. At post-pulse times, a peaked waveform of the target current is typical for the active phase of the plasma and can give information on the material composition of the ablated surface layers. The afterglow phase is determined by a current of electrons flowing from the target to the ground.
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Why is it important?
The experimental observations of target currents allow us to determine not only the total number of electrons escaping from the plasma in all directions but also the shot-to-shot reproducibility of the laser-matter interaction. Experiments also show that the time-resolved target current is very sensitive to the actual composition of the surface layer of irradiated target and to laser parameters.
Perspectives
One can achieve that the target current may become a new useful parameter in the field of the laser ablation–inductively coupled plasma mass spectrometry (LA–ICPMS).
Josef Krasa
Institute of Physics, Czech Academy of Sciences
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This page is a summary of: Target current: a useful parameter for characterizing laser ablation, Laser and Particle Beams, February 2017, Cambridge University Press,
DOI: 10.1017/s0263034617000040.
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