Laser-generated plasma plume expansion: Combined continuous-microscopic modeling

Abstract

The physical phenomena involved in the interaction of a laser-generated plasma plume with a background gas are studied numerically. A three-dimensional combined model is developed to describe the plasma plume formation and its expansion in vacuum or into a background gas. The proposed approach takes advantages of both continuous and microscopic descriptions. The simulation technique is suitable for the simulation of high-rate laser ablation for a wide range of background pressure. The model takes into account the mass diffusion and the energy exchange between the ablated and background species, as well as the collective motion of the ablated species and the background-gas particles. The developed approach is used to investigate the influence of the background gas on the expansion dynamics of the plume obtained during the laser ablation of aluminum. At moderate pressures, both plume and gas compressions are weak and the process is mainly governed by the diffusive mixing. At higher pressures, the interaction is determined by the plume-gas pressure interplay, the plume front is strongly compressed, and its center exhibits oscillations. In this case, the snowplough effect takes place, leading to the formation of a compressed gas layer in front of the plume. The background pressure needed for the beginning of the snowplough effect is determined from the plume and gas density profiles obtained at various pressures. Simulation results are compared with experimentally measured density distributions. It is shown that the calculations suggest localized formation of molecules during reactive laser ablation.

Pulsed laser ablation of complex oxides: The role of congruent ablation and preferential scattering for the film stoichiometry

“…25,26 This value can be even shorter for the ablated species located at the plume front, due to the increase of the background gas density consequent to the plume confinement. 27,28 Moreover, the confinement also influences the collisional dynamics of the inner plume species. 27 Thus, the plume species can suffer several collisions, both with the background gas molecules and among themselves, depending on the residual distance to the substrate, and time needed to reach it.…”

Insight into electronic mechanisms of nanosecond-laser ablation of silicon

“…24,25,[44][45][46] This relatively simple model gives a good description of experimental data on the material melting and ablation thresholds and on mass removal without using any adjusting parameters or with a minimum adjustment which, however, can be physically founded. By being incorporated into a number of combined approaches, [47][48][49][50][51][52] it has allowed a proper description of the interrelation between the target state and the laser-induced plume behavior including backward deposition of the ablated products. 50,52 In the model, the absorption of the laser light by the target material is described by the following general Beer-Lambert law, which implies a linear relationship between the absorptance and the concentration of absorbing centers:…”

Energy balance of a laser ablation plume expanding in a background gas

“…[9]. (c) Kinetic energy of the background gas from the PM-model compared with the kinetic energy of the external shockwave the space inside the sphere is dilute, but not empty [7,9,12]. However, a model with the plume mass distributed inside the shell becomes far more complex, and in view of the satisfactory agreement with the more complete model of Arnold et al [9], there is hardly any reason to extend the PM-model.…”

“…It is not included in the PM-model, and also for other models the predictions are not accurate around the stopping distance [9,16]. In the late stage, the diffusion of particles out of the plume volume becomes gradually more important [4,5,7,11,17].…”

“…PLD of a film by nanosecond lasers is an extremely complex process, which runs through several stages from ini-tial laser irradiation of a solid target, material ejection and transfer through vacuum or a background gas to a substrate [3][4][5]. A more comprehensive knowledge of plume dynamics in a background gas is clearly desirable, in particular because most of the existing treatments are limited to one or two target materials into a single background gas [6][7][8][9]. The expansion of a silicon ablation plume in helium and argon gases has been modeled quite comprehensively, but the results are difficult to apply to other plume-background gas systems [8].…”