Revealing of hydrodynamic and electrostatic factors in the center-of-mass velocity of an expanding plasma generated by pulsed laser ablation

Abstract

Time-of-flight spectra of C, Fe, and Si ions produced with the use of a KrF excimer laser have been analyzed. Ion currents were collected by Faraday cups and their responses were analyzed using a detector signal function. This function was derived from shifted Maxwell-Boltzmann velocity distribution, in order to uncover the contribution of partial currents of all the ionized species constituting the expanding plasma plume. The deconvolution method allowed to estimate parameters of the plasma, such as the ion temperature and the center-of-mass velocities of expanding ionized species. Furthermore, the linear charge-state dependence of the center-of-mass velocity has revealed the contribution of hydrodynamic and electrostatic forces to the expansion velocity of the plasma. The nearly isotropic distribution of the center-of-mass velocity indicates that the shape of the plasma plume is determined mainly by the angular distribution of the ionization degree of ions.

Neutral atomic jet generation by laser ablation of copper targets

“…8 These two works reinforce the idea that, for intensities lower than 1 × 10 14 W/cm 2 , the COM velocity has two main contributions: the first due to hydrodynamical expansion, as discussed by Kools and Baller, 9 and a second one due to the formation of an internal accelerating potential due to fast electrons, or 8…”

“…7,8 This behavior could explain why the COM velocity changes with the applied voltage in our experiments: the ions are gradually removed from the plume as the voltage increases, with the higher charge-state ion being removed first. However, all this mentioned works state that the COM velocity increases with the ion state-charge and, being so, the v COM should decrease with the applied voltage, since the faster particles are removed first, remaining the slower ones.…”

Characteristics of target polarization by laser ablation

“…The structure of ion fronts is revealed for a time τ = 1 μs after the laser-target interaction. The identification of groups of ionized hydrogen, hydrocarbon radicals, carbon, and Ta atoms constituting the ion front is based on the ion mass analysis described elsewhere (Torrisi et al, 2004;Krása et al, 2010;2011). Only H + , H 2 + , and C q+ are labeled as impurities in Figure 3.…”

“…A deconvolution of TOF spectrum to partial currents for each ionized species and charge state makes it possible to determine all partial ion fronts (Krása et al, 2011;. In this paper, we discuss the observed transient currents that balance both the deficit and surplus of electrons on various targets irradiated by a low-intensity excimer krypton fluoride (KrF) laser.…”

Atomic mass dependent electrostatic diagnostics of colliding laser plasma plumes

“…Although there are a limited number of reports on the ionic yield from laser plasma plumes for varying atomic mass, [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] to our knowledge, there have been no previous reports on colliding plasma plumes studies for varying target atomic mass. To further elucidate the behaviour of laser generated colliding plasma plumes, we have utilized a Faraday cup to record the time of flight (TOF) signals from 14 different target elements ( 12 C, 27 Al, 28 Si, 48 Ti, 52 Mn, 56 Fe, 64 Cu, 91 Zr, 96 Mo, 112 Cd, 115 In, 118 Sn, 184 W, and 207 Pb) using a fixed laser fluence (F ¼ 0.25 kJ cm À2 , I p ¼ 4.2 Â 10 10 W cm À2 ) for both single and colliding plasma configurations.…”