Target properties – Plasma dynamics relationship in laser ablation of metals: Common trends for fs, ps and ns irradiation regimes

Charged Particle Oscillations in Transient Plasmas Generated by Nanosecond Laser Ablation on Mg Target

“…The existence of coherent states implies that the individual ejected particles are coherent (through the double-layer characteristic to each laser ablation plasma structure), and there is a connecting tissue amongst the ablated particle cloud. This aspect of the laser-produced plasma was empirically showcased by our group in [10], where we show that at all laser ablation scales, there are mathematical functions connecting series of materials, a property that is inherent to a fractal model. As the particularity of a fractal model is the use of zoom in/zoom out processes, we can still find a coherence between the plasma structures (Coulomb or thermal).…”

“…Although during expansion, there are other phenomena that need to be considered like ion neutralization, secondary ionizations, or molecule formation [18], this shift in the floating potential showcases the change in the ion-to-electron ratio within the plasma volume for a fixed moment in time (1 µs).The spatiotemporal evolution of all main plasma parameters considered here (electron temperature and plasma potential) follow a classical quasi-exponential decrease. To determine the aforementioned plasma parameters, we treated the I−V characteristics following the procedure from [10,11]. Briefly, by applying a logarithm procedure to the I−V characteristic curve, we will obtain a distribution that is defined by a linear increase, an inflection point, and a saturation region.…”

“…The slope of that linear increase will define the electron temperature while the inflection point will be the plasma potential ( Figure 5e). Details on this procedure can also be seen in [10][11][12]. For a time-span of 6 μs using a step of 1 μs, we reconstruct the I-V characteristics for each moment in time.…”

“…Over time, a wide range of investigation techniques have been developed like optical emission spectroscopy [7][8][9], mass spectrometry [10], or Langmuir probes [11][12][13][14] (LP), and these have been implemented to highlight phenomena like plasma structuring [15,16], molecule formation [17,18], elemental distribution in complex plasmas, and ejected particle behavior in various conditions. Out of all the techniques presented in the literature, LPs have shown great versatility being implemented for a wide range of materials [11,19] and various irradiation conditions [10,20]. The LP method presents itself as a relatively simple diagnostic tool for plasma investigations, consisting of submerging a metallic electrode (of cylindrical, plane, or spherical geometry) in the plasma in order to record the ionic and electronic current or a mixture of the two currents, as selected by the applied voltage.…”

“…Laser-produced plasma (LPP) has a transient nature, with all its parameters presenting a complex spatial distribution and temporal dependence and being largely highly directional. The LP theory has been adapted for LPP by sampling the charged particle temporal traces and considering, besides the thermal movement, the drift movement of the ejected particle [10,11]. LP techniques offer insight into the ejected particle dynamics from a small plasma volume and, thus, can be implemented for axial and angular measurements, and it can easily be adapted for a wide range of diagnostics geometries.…”