Modeling of laser induced plasma, spectroscopic and time of flight experiments in pulsed laser deposition

Simulation study of the effect of recombination processes in an expanding plasma

“…Note that due to the kinematics of the three-body collision process, cf. (10) and (11), the energy of ions and neutrals perpendicular to the flow remains essentially unchanged,…”

“…After short-pulse laser irradiation of a target surface, a plasma cloud is formed in front of the surface, which consequently expands away from the surface [1][2][3]. The plasma-kinetic processes occurring during expansion are quite complex [4][5][6][7][8][9][10][11][12]. While the bulk of the cloud swiftly becomes quasi-neutral, a space-charge field develops at the expansion front; as a consequence, the ions in the cloud are accelerated at the cost of cooling the thermal energy of the electrons.…”

“…Collision processes in the plasma may modify this simple picture. While most elastic, and also inelastic, collisions may be appropriately understood as a friction force in a hydrodynamic modelling [9], the occurrence of recombination processes may lead to qualitatively novel features [10,13,14]. In addition to a change in the charge-state distribution of the plasma, three-body recombination changes the number of particles in the plasma and hence invariably increases the energy per particle.…”

“…It has been argued that such a segregation may result from the self-consistent electrostatic fields accelerating the ions in the plasma [16,17]. However, another approach relates the segregation to the recombination processes occurring in the plasma [10,18]. Since the recombination rate depends nonlinearly on the electron density, and even more strongly on the electron temperature, recombination is strongest close to the emitting surface and in the center of the cloud, and vanishes towards the expansion front.…”

“…We note that in previous plasma modelling and simulation approaches that include recombination processes, as a rule only a rate-equation approach is used. Different levels of sophistication have been reached ranging from a homogeneous plasma [18,21] to spatial one-dimensional time-dependent approaches [10], to the coupling of rate equations for the ionic component with a Fokker-Planck kinetic description of the electronic component [22]. A fully kinetic treatment of the electron and ion component, such as is attempted here, only rarely appears to have been performed [23,24].…”