Long-range oscillations of a laser-produced carbon plasma recorded by an electrostatic energy analyzer

Abstract

Understanding peculiar dynamics in transient laser-produced plasmas is of great importance for a number of applications such as energetic ion production, ion implantation, laser micro-machining, etc. Continuing a series of papers on the electrical and optical characterization of laser ablation plasma plumes, we report here on the observation of oscillations in the ionic and electronic currents at a long distance (17.5\u2009cm) from the ablation target. An electrostatic energy analyzer was used to finely probe the dynamics of charge carriers in a carbon plasma generated in vacuum by KrF excimer laser ablation of a graphite target. A short-time Fourier transform data processing approach was applied to extract valuable information from the recorded currents. This method not only reveals different frequencies for two distinct expanding plasma structures, but also unveils different trends in their temporal evolution. These new experimental results corroborate previous studies supporting a scenario based on the plasma structuring in multiple double layers. A discussion with respect to an alternative scenario based on low-frequency sheath instabilities is also presented.